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fn9178 rev 4.00 page 1 of 30 mar 9, 2006 fn9178 rev 4.00 mar 9, 2006 isl6566 three-phase buck pwm controller with integrated mosfet drivers for vrm9, vrm10, and amd hammer applications datasheet the isl6566 three-phase pw m control ic provides a precision voltage regulat ion system for advanced microprocessors. the integratio n of power mosfet drivers into the controller ic marks a departure from the separate pwm controller and dr iver configuration of previous multi- phase product families. by redu cing the number of external parts, this integration is opt imized for a cost and space saving power management solution. outstanding features of this controller ic include programmable vid codes com patible with intel vrm9, vrm10, as well as amd hamme r microprocessors. a unity gain, differential am plifier is provided for remote voltage sensing, compensating for any p otential difference between remote and local grounds. the output voltage can also be positively or negatively offse t through the use of a single external resistor. a unique feature of the isl6566 is the combined use of both dcr and r ds(on) current sensing. load line voltage positioning (droop) and overcurrent protection are accomplished through continuous inductor dcr current sensing, while r ds(on) current sensing is used for accurate channel-current balance. using both methods of current sampling utilizes the best adv antages of each technique. protection features of this c ontroller ic include a set of sophisticated overvoltage, u ndervoltage, and overcurrent protection. overvoltage result s in the converter turning the lower mosfets on to clamp the rising output voltage and protect the microprocessor. the overcurrent pro tection level is set through a single external resistor. furthermore, the isl6566 includes prot ection against an ope n circuit on the remote sensing inputs. combined, these features provide advanced protection for the microprocessor and power system. features ? integrated multi-phase power conversion - 1, 2, or 3-phase operation ? precision core voltage regulation - differential remote voltage sensing - ? 0.5% system accuracy over temperature - adjustable reference-voltage offset ? precision channel current sharing - uses loss-less r ds(on) current sampling ? accurate load line programming - uses loss-less inductor dcr current sampling ? variable gate drive bias: 5v to 12v ? microprocessor voltag e identification inputs - up to a 6-bit dac - selectable between inte ls vrm9, vrm10, or amd hammer dac codes - dynamic vid technology ? overcurrent protection ? multi-tiered overvoltage protection ? digital soft-start ? selectable operation frequ ency up to 1.5mh z per phase ? pb-free plus anneal available (rohs compliant) pinout isl6566 (qfn) top view vid1 vid3 vid4 enll pgood lgate1 vid2 fs pvcc1 isen1 ugate1 vid0 vid12.5 vrm10 ref ofs vcc comp fb vdiff 1 40 2 3 4 5 6 7 8 9 10 30 29 28 27 26 25 24 23 22 21 39 38 37 36 35 34 33 32 31 11 12 13 14 15 16 17 18 19 20 boot1 phase1 phase2 ugate2 boot2 isen2 pvcc2 lgate2 phase3 boot3 rgnd vsen ocset icomp isum iref lgate3 pvcc3 isen3 ugate3 41 gnd
isl6566 fn9178 rev 4.00 page 2 of 30 mar 9, 2006 ordering information part number part marking temp. (c) package pkg. dwg. # isl6566crr5184 isl6566cr 0 to 70 40 ld 6x6 qfn l40.6x6 isl6566cr-tr5184 isl6566cr 0 to 70 40 ld 6x6 qfn tape and reel l40. 6x6 ISL6566CRZR5184 (note) isl6566crz 0 to 70 40 ld 6x6 qfn (pb-free) l 40.6x6 isl6566crz-tr5184 (note) isl6566crz 0 to 70 40 ld 6x6 qfn (pb-free ) tape and reel l40.6x6 isl6566crzar5184 (note) isl6566crz 0 to 70 40 ld 6x6 qfn (pb-free) l40.6x6 isl6566crza-tr5184 (note) isl6566crz 0 to 70 40 ld 6x6 qfn (pb-fre e) tape and reel l40.6x6 isl6566ir isl6566ir -40 to 85 40 ld 6x6 qfn l40.6x6 isl6566ir-t isl6566ir -40 to 85 40 ld 6x6 qfn tape and reel l40.6x6 isl6566irz (note) isl6566irz -40 to 85 40 ld 6x6 qfn (pb-free) l40. 6x6 isl6566irz-t (note) isl6566irz -40 to 85 40 ld 6x6 qfn (pb-free) t ape and reel l40.6x6 isl6566irza (note) isl6566irz -40 to 85 40 ld 6x6 qfn (pb-free) l40 .6x6 isl6566irza-t (note) isl6566irz -40 to 85 40 ld 6x6 qfn (pb-free) l 40.6x6 note: intersil pb-free plus anneal products employ special pb-fr ee material sets; molding compounds/die attach materials and 10 0% matte tin plate termination finish, which are rohs compliant and compatible wit h both snpb and pb-free soldering operations. intersil pb-free products are msl classified at pb-free peak reflow temperatures that meet or exceed the pb- free requirements of ipc/jedec j std-020.
isl6566 fn9178 rev 4.00 page 3 of 30 mar 9, 2006 block diagram vid4 dynamic vid d/a vid3 vid2 vid1 vid0 vid12.5 vrm10 e/a ref fb offset ofs comp isum iref icomp isen amp oc ocset rgnd vsen vdiff x1 100 ? a +150mv ovp x 0.82 ovp uvp isen1 isen2 isen3 channel current sense ? 1 n ? pwm1 ? ? pwm3 channel current balance through shoot- protection boot1 ugate1 phase1 lgate1 pvcc1 logic control gate through shoot- protection boot2 ugate2 phase2 lgate2 pvcc2 logic control gate through shoot- protection boot3 ugate3 phase3 lgate3 pvcc3 logic control gate clock and generator sawtooth soft-start and fault logic channel detect vcc reset power-on 0.66v enll fs pgood gnd 0.2v +1v pwm2 x1 v ovp
isl6566 fn9178 rev 4.00 page 4 of 30 mar 9, 2006 typical application - isl6566 vid3 vid4 pgood vid2 vid1 vid0 vdiff fb comp vcc isen1 isl6566 vid12.5 fs ofs ref +12v phase1 ugate1 boot1 lgate1 isum icomp iref load vsen rgnd ocset vrm10 +5v pvcc1 enll +12v gnd isen2 +12v phase2 ugate2 boot2 lgate2 pvcc2 isen3 +12v phase3 ugate3 boot3 lgate3 pvcc3
isl6566 fn9178 rev 4.00 page 5 of 30 mar 9, 2006 typical application - isl6566 with ntc thermal compensation isum icomp iref ocset ntc place in close proximity vid3 vid4 pgood vid2 vid1 vid0 vdiff fb comp vcc isen1 isl6566 vid12.5 fs ofs ref +12v phase1 ugate1 boot1 lgate1 load vsen rgnd vrm10 +5v pvcc1 enll +12v gnd isen2 +12v phase2 ugate2 boot2 lgate2 pvcc2 isen3 +12v phase3 ugate3 boot3 lgate3 pvcc3
isl6566 fn9178 rev 4.00 page 6 of 30 mar 9, 2006 absolute maximum ratings supply voltage, vcc . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3v to +6v supply voltage, pvcc . . . . . . . . . . . . . . . . . . . . . . . . . -0.3v to +15v absolute boot voltage, v boot . . . . . . . . gnd - 0.3v to gnd + 36v phase voltage, v phase . . . . . . . . gnd - 0.3v to 15v (pvcc = 12) gnd - 8v (<400ns, 20j) to 24v (<200ns, v boot-phase = 12v) upper gate voltage, v ugate . . . . v phase - 0.3v to v boot + 0.3v v phase - 3.5v (<100ns pulse width, 2j) to v boot + 0.3v lower gate voltage, v lgate . . . . . . . . gnd - 0.3v to pvcc + 0.3v gnd - 5v (<100ns pulse width, 2j) to pvcc+ 0.3v input, output, or i/o voltage . . . . . . . . . gnd - 0.3v to v cc + 0.3v esd classification . . . . . . . . . . . . . . . . . . . . . . . class i jedec std recommended operating conditions vcc supply voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +5v ? 5% pvcc supply voltage . . . . . . . . . . . . . . . . . . . . . . . +5v to 12v ? 5% ambient temperature (isl6566cr, isl6566crz) . . . . 0c to 70c ambient temperature (isl6566ir, isl6566irz) . . . . .-40c to 85 c thermal information thermal resistance ? ja (c/w) ? jc (c/w) qfn package (notes 1, 2) . . . . . . . . . . 32 3.5 maximum junction temperature . . . . . . . . . . . . . . . . . . . . . . . 150c maximum storage temperature range . . . . . . . . . . . -65c to 150c maximum lead temperature (soldering 10s) . . . . . . . . . . . . . 300c caution: stress above those listed in ?absolute maximum ratings? may cause permanent damage to the device. this is a stress onl y rating and operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. notes: 1. ? ja is measured in free air with the component mounted on a high e ffective thermal conductivity t est board with direct attach f eatures. see tech brief tb379. 2. for ? jc , the case temp location is the center of the exposed metal p ad on the package underside. electrical specifications recommended operating conditions, unless otherwise specified. parameter test conditions min typ max units bias supply and internal oscillator input bias supply current i vcc ; enll = high - 15 20 ma gate drive bias current i pvcc ; enll = high - 0.8 - ma vcc por (power-on reset) threshold vcc rising 4.25 4.38 4.50 v vcc falling 3.75 3.88 4.00 v pvcc por (power-on reset) threshold pvcc rising 4.25 4.38 4.50 v pvcc falling 3.60 3.88 4.00 v oscillator ramp amplitude (note 3) v pp -1.50-v maximum duty cycle (note 3) - 66.6 - % oscillator frequency, f sw r t = 100k ? ( ?? ?? 1%) 225 250 275 khz control thresholds enll rising threshold -0.66-v enll hysteresis - 100 - mv comp shutdown threshold comp falling 0.2 0.3 0.4 v reference and dac system accuracy (vid = 1.0v - 1.850v) -0.5 - 0.5 % system accuracy (vid = 0.8v - 1.0v) -0.8 - 0.8 % dac input low voltage (vr9, vr10) --0.4v dac input high voltage (vr9, vr10) 0.8 - - v dac input low voltage (amd) --0.6v dac input high voltage (amd) 1.0 - - v ofs sink current accuracy (negative offset) r ofs = 30k ?? from ofs to vcc 47.5 50.0 52.5 ? a ofs source current accuracy (positive offset) r ofs = 10k ?? from ofs to gnd 47.5 50.0 52.5 ? a
isl6566 fn9178 rev 4.00 page 7 of 30 mar 9, 2006 error amplifier dc gain (note 3) r l = 10k to ground - 96 - db gain-bandwidth product (note 3) c l = 100pf, r l = 10k to ground - 20 - mhz slew rate (note 3) c l = 100pf, load = ? 400 ? a-8-v/ ? s maximum output voltage load = 1ma 3.90 4.20 - v minimum output voltage load = -1ma - 0.85 1.0 v overcurrent protection ocset trip current 93 100 107 ? a ocset accuracy ocset and isum difference -5 0 5 mv icomp offset -5 0 5 mv protection undervoltage threshold vsen falling 80 82 84 %vid undervoltage hysteresis vsen rising - 3 - %vid overvoltage threshold while ic disabled v ovp , vrm9.0 configuration 1.92 1.97 2.02 v v ovp , hammer and vrm10.0 configurations 1.62 1.67 1.72 v overvoltage threshold vsen rising vid + 125mv vid + 150mv vid + 175mv v overvoltage hysteresis vsen falling - 50 - mv open sense-line protection thres hold iref rising and falling vdif f + 0.9v vdiff + 1v vdiff + 1.1v v switching time (note 3) ugate rise time t rugate; v pvcc = 12v, 3nf load, 10% to 90% - 26 - ns lgate rise time t rlgate; v pvcc = 12v, 3nf load, 10% to 90% - 18 - ns ugate fall time t fugate; v pvcc = 12v, 3nf load, 90% to 10% - 18 - ns lgate fall time t flgate; v pvcc = 12v, 3nf load, 90% to 10% - 12 - ns ugate turn-on non-overlap t pdhugate ; v pvcc = 12v, 3nf load, adaptive - 10 - ns lgate turn-on non-overlap t pdhlgate ; v pvcc = 12v, 3nf load, adaptive - 10 - ns gate drive resistance (note 3) upper drive source resistance v pvcc = 12v, 15ma source current 1.25 2.0 3.0 ? upper drive sink resistance v pvcc = 12v, 15ma sink current 0.9 1.65 3.0 ? lower drive source resistance v pvcc = 12v, 15ma source current 0.85 1.25 2.2 ? lower drive sink resistance v pvcc = 12v, 15ma sink current 0.60 0.80 1.35 ? over temperature shutdown thermal shutdown setpoint (note 3) - 160 - c thermal recovery setpoint (note 3) - 100 - c note: 3. parameter magnitude guaranteed by design. not 100% tested. electrical specifications recommended operating conditions, unless otherwise specified. (continued) parameter test conditions min typ max units
isl6566 fn9178 rev 4.00 page 8 of 30 mar 9, 2006 timing diagram simplified power system diagram functional pin description vcc vcc is the bias suppl y for the ics small-signal circuitry. connect this pin to a +5v supp ly and locally decouple using a quality 1.0 ? f ceramic capacitor. pvcc1, pvcc2, pvcc3 these pins are the power suppl y pins for the corresponding channel mosfet drive, and can be connected to any voltage from +5v to +12v, depending on the desired mosfet gate drive level. the number of active channels is determined by the state of pvcc2 and pvcc3. leave pvcc3 unconnected or grounded for 2-phase operati on. for 1-phase operation leave both pvcc3 and pv cc2 unconnected or grounded. gnd gnd is the bias and refe rence ground for the ic. enll this pin is a threshold-sensitive (approximately 0.66v) enable input for the controller. held l ow, this pin disab les controlle r operation. pulled high, the pin enables the controller for operation. enll has a internal 1.0 ? a pull-up to 5v. fs a resistor, placed from fs to g round, will set the switching frequency. refer to equation 34 for proper resistor calculation. ugate lgate t flgate t pdhugate t rugate t fugate t pdhlgate t rlgate channel1 +5v in v out q1 q2 isl6566 channel2 q3 q4 dac 5-6 vid channel3 q5 q6 +12v in
isl6566 fn9178 rev 4.00 page 9 of 30 mar 9, 2006 vid4, vid3, vid2, vid1, vid0, and vid12.5 these are the inputs for the internal dac that provides the reference voltage for output regulation. these pins respond to ttl logic thresholds. the is l6566 decodes the vid inputs to establish the output voltage; see vid tables for correspondence between dac c odes and output voltage settings. these pins are int ernally pulled high, to approximately 1.2v, by 40 ? a (typically) internal current sources; the internal pull-up cur rent decreases to 0 as the vid voltage approaches the internal pull-up voltage. all vid pins are compatible with external pull-up voltages not exceeding the ics bias voltage (vcc). vrm10 this pin selects vrm10.0 dac compliance when pulled high or open. if vrm10 is grounded, vid12.5 selects the compliance standard for the internal dac: pulled to ground, it encodes the dac with amd hammer vid co des, while left open or pulled high, it encodes the dac with intel vrm9.0 codes. vsen and rgnd vsen and rgnd are inputs to the precision differential remote-sense amplifier and should be connected to the sense pins of the remote load. icomp, isum, and iref isum, iref, and icomp are the dcr current sense amplifiers negative input, positive input, and output respectively. for accurate d cr current sensing, connect a resistor from each channels phase node to isum and connect iref to the summing point of the output inductors, roughly vout. a parallel r- c feedback circuit connected between isum and icomp will then create a voltage from iref to icomp proportional to the voltage drop across the inductor dcr. this voltage is referred to as the droop voltage and is added to the differential r emote-sense amplifier output. note: an optional 0.01 ? f ceramic capacitor can be placed from the iref pin to the isum p in, or from the iref pin to gnd to help reduce any noise affects that may occur due to layout. vdiff vdiff is the output of the differ ential remote-sense amplifier. the voltage on this pin is equal to the difference between vsen and rgnd added to the difference between iref and icomp. vdiff therefore represents the output voltage plus the droop voltage. fb and comp these pins are the internal error amplifier inverting input and output respectively. fb, vdif f, and comp are tied together through external r-c networks to compensate the regulator. ref the ref input pin is the positiv e input of the er ror amplifier. it is internally connected to t he dac output through a 1k ? resistor. a capacitor is used between the ref pin and ground to smooth the voltage trans ition during dynamic vid operations. ofs the ofs pin provides a means to program a dc current for generating an offset voltage ac ross the resistor between fb and vdiff. the offset current i s generated via an external resistor and precision internal voltage references. the polarit y of the offset is selected by connecting the resistor to gnd or vcc. for no offset, the ofs pin should be left unconnected. ocset this is the overcurrent set pin. placing a resistor from ocset to icomp allows a 100 ? a current to flow out this pin, producing a voltage reference. i nternal circuitry compares the voltage at ocset to the voltage at isum, and if isum ever exceeds ocset, the overcurr ent protection activates. isen1, isen2 and isen3 these pins are used for balanc ing the channel currents by sensing the current through each channels lower mosfet when it is conducting. connec t a resistor between the isen1, isen2, and isen3 pins and their respective phase node. this resistor sets a curr ent proportional to the current in the lower mosfet during its conduction interval. ugate1, ugate2, and ugate3 connect these pins to the c orresponding upper mosfet gates. these pins are used t o control the upper mosfets and are monitored for shoot-t hrough prevention purposes. maximum individual channel dut y cycle is limited to 66%. boot1, boot2, and boot3 these pins provide the bias voltage for the corresponding upper mosfet drives. connect t hese pins to appropriately- chosen external bootstrap capa citors. internal bootstrap diodes connected to the pvcc pins provide the necessary bootstrap charge. phase1, phase2, and phase3 connect these pins to the sou rces of the corresponding upper mosfets. these pins a re the return path for the upper mosfet drives. lgate1, lgate2, and lgate3 these pins are used to control the lower mosfets. connect these pins to the correspo nding lower mosfets gates. pgood during normal operation pgood indicates whether the output voltage is within specified overvoltage and undervoltage limits. if the outpu t voltage exceeds these limits or a reset event o ccurs (such as an overcurrent event), pgood is pulled low. pgood is always low prior to the end of soft-start.
isl6566 fn9178 rev 4.00 page 10 of 30 mar 9, 2006 operation multi-phase power conversion microprocessor load current pro files have changed to the point that the advantages of m ulti-phase power conversion are impossible to ignore. the technical challenges associated with producing a si ngle-phase converter that is both cost-effective and therma lly viable have forced a change to the cost-saving appr oach of multi-phase. the isl6566 controller helps si mplify implementation by integrating vital functions and requiring minimal external components. the block diagram on page 3 provides a top level view of multi-phase power conversion using the isl6566 controller. interleaving the switching of each channel i n a multi-phase converter is timed to be symmetrically out o f phase with each of the other channels. in a 3-phase converte r, each channel switches 1/3 cycle after the previous chann el and 1/3 cycl e before the following channel. as a result, the three-phase converter has a combined ripple frequency th ree times greater than the ripple frequency of any one phas e. in addition, the peak-to- peak amplitude of the combined inductor currents is reduced in proportion to the number of phases (equations 1 and 2). increased ripple frequency and lower ripple amplitude mean that the designer can use less per-channel inductance and lower total output capacitance for any performance specification. figure 1 illustrates t he multiplicative effect on output ripple frequency. the three channel c urrents (il1, il2, and il3) combine to form the ac rippl e current and the dc load current. the ripple component has three times the ripple frequency of each individual channel current. each pwm pulse is terminated 1/3 of a cyc le after the pwm pulse of the previous phase. the peak-to-pea k current for each phase is about 7a, and the dc component s of the inductor currents combine to feed the load. to understand the reduction of ripple current amplitude in the multi-phase circuit, examine the equation representing an individual channel peak-to-peak inductor current. in equation 1, v in and v out are the input and output voltages respectively, l is the single-channel inductor value, and f s is the switching frequency. the output capacitors conduct the ripple component of the inductor current. in the case of multi-phase converters, the capacitor current is the sum of the ripple currents from each of the individual channels. compare equat ion 1 to the expression for the peak-to-peak current after the summation of n symmetrically phase-shi fted inductor currents in equation 2. peak-to-peak rippl e current decreases by an amount proportional to the number of channels. output- voltage ripple is a function o f capacitance, capacitor equivalent series resistance (esr), and inductor ripple current. reducing the inductor ripple current allows the designer to use fewer or less costly output capacitors. another benefit of interleavin g is to reduce input ripple current. input capacitance is determined in part by the maximum input ripple current. multi-phase topologies can improve overall system cost and size by lowering input ripple current and allowing the designer to reduce the cost of input capacitance. the example in f igure 2 illustrates input currents from a three-phase c onverter combining to reduce the total input ripple current. the converter depicted in figure 2 delivers 1.5v to a 36a load from a 12v input. the rms inpu t capacitor current is 5.9a. compare this to a single-phase converter also stepping down 12v to 1.5v at 36a. the singl e-phase converte r has 11.9a rms input capacitor curren t. the single-phase converter must use an input capacitor bank with twice the rms current capacity as the equivalent three-phase converter. figure 1. pwm and inductor-current waveforms for 3-phase converter 1 ? s/div pwm2, 5v/div pwm1, 5v/div il2, 7a/div il1, 7a/div il1 + il2 + il3, 7a/div il3, 7a/div pwm3, 5v/div i pp v in v out C ?? v out lf s v in ----------------------------------------------------- - = (eq. 1) i cpp , v in nv out C ?? v out lf s v in ----------------------------------------------------------- - = (eq. 2) figure 2. channel input currents and input- capacitor rms current for 3-phase converter channel 1 input current 10a/div channel 2 input current 10a/div channel 3 input current 10a/div input-capacitor current, 10a/div 1 ? s/div
isl6566 fn9178 rev 4.00 page 11 of 30 mar 9, 2006 figures 22 and 23 in t he section entitled input capacitor selection can be used to determine the input-capacitor rms current based on load current, duty cycle, and the number of channels. they are provided as aids in determining the optimal input capacitor solution. pwm operation the timing of each converter leg is set by the number of active channels. the default channel setting for the isl6566 is three. one switching cycle is defin ed as the time between the internal pwm1 pulse termination signals. the pulse termination signal is the inte rnally generated clock signal that triggers the fa lling edge of pwm 1. the cycle time of the pulse termination signal is th e inverse of the switching frequency set by the resistor between the fs pin and ground. each cycle begins when the clock signal commands pwm1 to go low. the pwm1 transition signals the internal channel-1 mosfet driver to turn off the channel-1 upper mosfet and turn on the chan nel-1 synchronous mosfet. in the default channel configuration, the pwm2 pulse terminates 1/3 of a cycle after the pwm1 pulse. th e pwm3 pulse terminates 1/3 o f a cycle after pwm2. if pvcc3 is left open or co nnected to ground, two channel operation is selected and the pwm2 pulse terminates 1/2 of a cycle after the pwm1 pulse t erminates. if both pvcc3 and pvcc2 are left open or connected to ground, single channel operation is selected. once a pwm pulse transitions low, it is hel d low for a minimum of 1/3 cycle. this forced off ti me is required to ensure an accurate current sample. current sensing is described in the next section. a fter the forced off time expires, the pwm output is e nabled. the pwm output state is driven by the posit ion of the error ampl ifier output signal, v comp , minus the current correct ion signal relative to the sawtooth ramp as illustrated in figure 3. when the modified v comp voltage crosses the sawtooth ramp, the pwm output transitions high. the internal mosfet driver detects the change in state of the pw m signal and turns off the synchronous mosfet and turns on the upper mosfet. the pwm signal will remain high until the pulse termination signal marks the begi nning of the next cycle by triggering the pwm signal low. channel-current balance one important benefit of multi- phase operation is the thermal advantage gained by distributi ng the dissipated heat over multiple devices and greater ar ea. by doing this the designer avoids the complexity of drivi ng parallel mosfets and the expense of using expe nsive heat sinks an d exotic magnetic materials. in order to realize the thermal advantage, it is i mportant that each channel in a multi-phase converter be controlled to carry about the same amount of current at any load level. to achieve this, the currents th rough each channel must be sampled every switching cycl e. the sampled currents, i n , from each active channel are summed together and divided by the number of active ch annels. the re sulting cycle average current, i avg , provides a measure of the total load- current demand on th e converter durin g each switching cycle. channel-current balance is achieved by comparing the sampled current of each channel to the cycle average current, and making the proper adjustment to each channel pulse width based on the error. intersils patented current- balance method is illustrat ed in figure 3, with error correction for channel 1 represen ted. in the figure, the cycle average current, i avg , is compared wit h the channel 1 sample, i 1 , to create an error signal i er . the filtered error signal modifies the pulse width commanded by v comp to correct any unbalance and force i er toward zero. the same method for error signal correction is applied to each active channel. current sampling in order to realize proper cu rrent-balance, the currents in each channel must be sampled every switching cycle. this sampling occurs during the forced off-time, following a pwm transition low. during this tim e the current-sense amplifier uses the isen inputs to repro duce a signal proportional to the inductor current, i l . this sensed current, i sen , is simply a scaled version of the inductor current. the sample window opens exactly 1/6 of t he switching period, t sw , after the pwm transitions low. the sample window then stays open the rest of the switching cycle until pwm trans itions high again, as illustrated in figure 4. the sampled current, at the end of the t sample , is proportional to the inductor curr ent and is held until the next switching period sample. the s ampled current is used only for channel-current balance. figure 3. channel-1 pwm function and current- balance adjustment ?? n i avg i 3 i 2 ? - + + - + - f(s) pwm1 i 1 v comp sawtooth signal i er note: channel 2 and 3 are optional. filter to gate control logic
isl6566 fn9178 rev 4.00 page 12 of 30 mar 9, 2006 the isl6566 sup ports mosfet r ds(on) current sensing to sample each channels current for channel-current balance. the internal circuitry, shown in figure 5 represents channel n of an n-channel conv erter. this circuitry is repeated for each channel in the converter, but may not be active depending on the status of th e pvcc3 and pvcc2 pins, as described in the pwm operation section. the isl6566 senses the channel load current by sampling the voltage across the lower mosfet r ds(on) , as shown in figure 5. a ground-referenced o perational amplifier, internal to the isl6566, is co nnected to the phase node through a resistor, r isen . the voltage across r isen is equivalent to the voltage drop across the r ds(on) of the lower mosfet while it is conducting. the res ulting current into the isen pin is proportional to the channel current, i l . the isen current is sampled and held as described in the current sampling section. from figure 5, the following equation for i n is derived where i l is the channel current. output voltage setting the isl6566 uses a digital to analog converter (dac) to generate a reference voltage base d on the logic signals at the vid pins. the dac decodes the 5 or 6-bit logic signals into one of the discrete vo ltages shown in t ables 2, 3, and 4. each vid pin is pulled up to an internal 1.2v voltage by a weak current source (40 ? a current), which decreases to 0 as the voltage at the vi d pin varies from 0 to the internal 1.2v pull-up voltage. external pull -up resistors or active-high output stages can augment the pull-up current sources, up to a voltage of 5v. . the isl6566 accommodates three different dac ranges: intel vrm9.0, amd hammer, or intel vrm10.0. the state of the vrm10 and vid12.5 pins decide which dac version is active. refer to table 1 for a description of how to select the desired dac version. figure 4. sample and hold timing time pwm i l i sen switching period sampling period old sample current new sample current figure 5. isl6566 internal and external current- sensing circuitry for current balance i n i sen i l r ds on ?? r isen ------------------------- - = - + isen(n) r isen sample & hold isl6565a internal circuit external circuit v in channel n upper mosfet channel n lower mosfet - + i l r ds on ?? i l i n i l r ds on ?? r isen ---------------------- = (eq. 3) table 1. isl6566 dac select table dac version vrm10 pin vid12.5 pin vrm10.0 high - vrm9.0 low high amd hammer low low table 2. amd hammer voltage identification codes vid4 vid3 vid2 vid1 vid0 vdac 11111off 111100.800 111010.825 111000.850 110110.875 110100.900 110010.925 110000.950 101110.975 101101.000 101011.025 101001.050 100111.075 100101.100 100011.125 100001.150 011111.175 011101.200 011011.225 011001.250 010111.275 010101.300
isl6566 fn9178 rev 4.00 page 13 of 30 mar 9, 2006 010011.325 010001.350 001111.375 001101.400 001011.425 001001.450 000111.475 000101.500 000011.525 000001.550 table 3. vrm9 voltage identification codes vid4 vid3 vid2 vid1 vid0 vdac 11111off 111101.100 111011.125 111001.150 110111.175 110101.200 110011.225 110001.250 101111.275 101101.300 101011.325 101001.350 100111.375 100101.400 100011.425 100001.450 011111.475 011101.500 011011.525 011001.550 010111.575 010101.600 010011.625 010001.650 001111.675 001101.700 001011.725 table 2. amd hammer voltage identification codes vid4 vid3 vid2 vid1 vid0 vdac 001001.750 000111.775 000101.800 000011.825 000001.850 table 4. vrm10 voltage identification codes vid4 vid3 vid2 vid1 vid0 vid12.5 vdac 111111off 111110off 0101000.8375 0100110.8500 0100100.8625 0100010.8750 0100000.8875 0011110.9000 0011100.9125 0011010.9250 0011000.9375 0010110.9500 0010100.9625 0010010.9750 0010000.9875 0001111.0000 0001101.0125 0001011.0250 0001001.0375 0000111.0500 0000101.0625 0000011.0750 0000001.0875 1111011.1000 1111001.1125 1110111.1250 1110101.1375 1110011.1500 1110001.1625 1101111.1750 1101101.1875 1101011.2000 table 3. vrm9 voltage identification codes (continued) vid4 vid3 vid2 vid1 vid0 vdac
isl6566 fn9178 rev 4.00 page 14 of 30 mar 9, 2006 voltage regulation in order to regulate the output voltage to a specified level, the isl6566 uses the integrating compensation network shown in figure 6. this compen sation network insures that the steady-state error in the ou tput voltage is limited only to the error in the reference vo ltage (output o f the dac) and offset errors in the ofs curr ent source, rem ote-sense and error amplifiers. intersil specifies the guaranteed tolerance o f the isl6566 to include the comb ined tolerances of each of these elements. the isl6566 incorporates an i nternal differential remote- sense amplifier in the feedback path. the amplifier removes the voltage error encountered when measuring the output voltage relative to the controller ground reference point, resulting in a more accura te means of sensing output voltage. connect the microproc essor sense pins to the non- inverting input, vsen, and i nverting input, rgnd, of the remote-sense amplifier. the droop voltage, v droop , also feeds into the remote-sense a mplifier. the remote-sense output, v diff , is therefore equal to the sum of the output voltage, v out , and the droop voltage. v diff is connected to the inverting input of the error amplifier through an external resistor. the output of the error amplifier, v comp , is compared to the sawtooth waveform to generate the pwm signals. the pwm signals control the timing of t he internal mosfet drivers and regulate the converter output so that the voltage at fb is equal to the voltage at ref. thi s will regulate the output voltage to be equal to equation 4. the internal and external circuitry that controls voltage regulation is illustrated in figure 6. load-line (droop) regulation some microprocessor manufact urers require a precisely- controlled output impedance . this dependenc e of output voltage on load current is oft en termed droop or load line regulation. 1 1 0 1 0 0 1.2125 1 1 0 0 1 1 1.2250 1 1 0 0 1 0 1.2375 1 1 0 0 0 1 1.2500 1 1 0 0 0 0 1.2625 1 0 1 1 1 1 1.2750 1 0 1 1 1 0 1.2875 1011011.300 1 0 1 1 0 0 1.3125 1 0 1 0 1 1 1.3250 1 0 1 0 1 0 1.3375 1 0 1 0 0 1 1.3500 1 0 1 0 0 0 1.3625 1 0 0 1 1 1 1.3750 1 0 0 1 1 0 1.3875 1 0 0 1 0 1 1.4000 1 0 0 1 0 0 1.4125 1 0 0 0 1 1 1.4250 1 0 0 0 1 0 1.4375 1 0 0 0 0 1 1.4500 1 0 0 0 0 0 1.4625 0 1 1 1 1 1 1.4750 0 1 1 1 1 0 1.4875 0 1 1 1 0 1 1.5000 0 1 1 1 0 0 1.5125 0 1 1 0 1 1 1.5250 0 1 1 0 1 0 1.5375 0 1 1 0 0 1 1.5500 0 1 1 0 0 0 1.5625 0 1 0 1 1 1 1.5750 0 1 0 1 1 0 1.5875 0 1 0 1 0 1 1.6000 table 4. vrm10 voltage identification codes (continued) vid4 vid3 vid2 vid1 vid0 vid12.5 vdac figure 6. output voltage and load-line regulation with offset adjustment i ofs external circuit isl6566 internal circuit comp r c r fb fb vdiff vsen rgnd - + v ofs error amplifier - + differential remote-sense amplifier v comp c c ref c ref - + vid dac 1k iref icomp + - + v droop - + v out - v out v ref v ofs C v droop C = (eq. 4)
isl6566 fn9178 rev 4.00 page 15 of 30 mar 9, 2006 as shown in figure 6, a voltage, v droop , proportional to the total current in all active channels, i out , feeds into the differential remote- sense amplifier. the resulting voltage at the output of the remote-sense amplifier is the sum of the output voltage and th e droop voltage. as equation 4 shows, feeding this voltage into the co mpensation network causes the regulator to adjust the out put voltage so that its equal t o the reference voltage mi nus the droop voltage. the droop voltage, v droop , is created by sensing the current through the output inductors. this is accomplished by using a continuous dcr current sensing method. inductor windings have a characteristic distributed resistance or dcr (direct current resistance). for simplicity, the inductor dcr is considered as a separate lumped quantity, as shown in figure 7. the channel current, i l , flowing through the inductor , passes through the dcr. equation 5 shows the s-domain equivalent voltage, v l , across the inductor. the inductor dcr is important because the voltage dropped across it is proportional to t he channel current. by using a simple r-c network and a current sense amplifier, as shown in figure 7, the voltage drop across all of the inductors dcrs can be extracted. the output of the current sense amplifier, v droop , can be shown to be pr oportional to the channel currents i l1 , i l2 , and i l3 , shown in equation 6. if the r-c network component s are selected such that the r-c time constant matches the inductor l/dcr time constant, then v droop is equal to the sum of the voltage drops across the individual dcrs , multiplied by a gain. as equation 7 shows, v droop is therefore proportional to the total output current, i out . by simply adjusting the value of r s , the load line can be set to any level, giving the converte r the right amount of droop at all load currents. it may also be necessary to compensate for any changes in dcr due to tem perature. these changes cause the load line to be skew ed, and cause the r-c time constant to not match the l/dcr time constant. if this becomes a problem a simple negative temperature coefficient resistor network can be used in the place of r comp to compensate for the rise in dcr due to temperature. note: an optional 10nf ceramic capacitor from the isum pin to the iref pin is reco mmended to help reduce any noise affects on the current s ense amplifier due to layout. output-voltage offset programming the isl6566 allows the designe r to accurately adjust the offset voltage by connecting a resistor, r ofs , from the ofs pin to vcc or gnd. when r ofs is connected between ofs and vcc, the voltage across i t is regulated to 1.5v. this causes a proportional current (i ofs ) to flow into the ofs pin and out of the fb pin. if r ofs is connected to ground, the voltage across it is regulated to 0.5v, and i ofs flows into the fb pin and out of the ofs pin. the offset current flowing through the resistor between vdiff and fb will generate the desired offset voltage whi ch is equal to the product (i ofs x r fb ). these functions are shown in figures 8 and 9. v l s ?? i l sl dcr + ? ?? ? = (eq. 5) v droop s ?? sl ? dcr ------------- 1 + ?? ?? sr comp c comp ?? 1 + ?? --------------------------------------------------------------- ----------- r comp r s ----------------------- i l1 i l2 i l3 ++ ?? dcr ?? ? = (eq. 6) v droop r comp r s --------------------- i out dcr ?? = (eq. 7) figure 7. dcr sensing configuration - + icomp r s dcr l inductor v out c out i l 1 - + v l (s) dcr l inductor dcr l inductor phase1 phase2 phase3 i l 2 i l 3 r s r s r comp c comp isum iref isl6566 - + v droop i out (optional)
isl6566 fn9178 rev 4.00 page 16 of 30 mar 9, 2006 once the desired output offset voltage has been determined, use the following formulas to set r ofs : for positive offset (connect r ofs to gnd): for negative offset (connect r ofs to vcc): dynamic vid modern microprocessors need to make changes to their core voltage as part of normal operation. they direct the core- voltage regulator to do this b y making changes to the vid inputs. the core-voltage regulator is required to monitor the dac inputs and respond to on- the-fly vid changes in a controlled manner, supervising a safe output voltage transition without discontinuity or disruption. the dac mode the is l6566 is operating in determines how the controller responds to a d ynamic vid change. when in vrm10 mode the is l6566 checks the vid inputs six times every switching cycle. if a new code is estab lished and it stays the same for 3 consec utive readings, the isl6566 recognizes the change and inc rements the reference. specific to vrm10, the proc essor controls the vid transitions and is respons ible for incrementing or decrementing one vid step at a time. in vrm 10 setting, the isl6566 will immediately change the reference to the new requested value as soon as t he request is validated; in cases where th e reference step is t oo large, the sudden change can trigger overcurr ent or overvoltage events. in order to ensure t he smooth transition of output voltage during a vrm10 vid change, a vid step change smoothing network is required for an isl6566 based voltage regulator. this network is composed of a 1k ? internal resistor between the output of dac and the capacitor c ref , between the ref pin and ground. the selection of c ref is based on the time duration for 1 bit vid change a nd the allowable delay time. assuming the microprocessor co ntrols the vid change at 1 bit every t vid , the relationship between c ref and t vid is given by equation 10. as an example, for a vid step change rate of 5 ? s per bit, the value of c ref is 22nf based on equation 10. when running in vrm9 or a md hammer operation, the isl6566 responds slightly diffe rent to a dynamic vid change than when in vrm10 mode. in the se modes the vid code can be changed by more than a 1-b it step at a time. once the controller receives the new vid c ode it waits half of a phase cycle and then begins slewing the dac 12.5mv every phase cycle, until the vid and dac ar e equal. thus, the total time required for a vid change, t dvid , is dependent on the switching frequency (f s ), the size of the change ( ? v vid ), and the time required to register the vid c hange. the one-cycl e addition in the t dvid equation is due to the po ssibility that the vid code change may occur up to one full switching cycle before being recognized. the approximate t ime required for a isl6566- based converter in amd hamme r configuration running at f s = 335khz to make a 1.1v to 1.5v reference voltage change is about 100 ? s, as calculated using the following equation. e/a fb ofs vcc gnd + - + - 0.5v 1.5v gnd r ofs r fb vdiff isl6566 figure 8. positive offset output voltage programming vref v ofs + - i ofs e/a fb ofs vcc gnd + - + - 0.5v 1.5v vcc r ofs r fb vdiff isl6566 figure 9. negative offset output voltage programming vref v ofs + - i ofs (eq. 8) r ofs 0.5 r fb ? v offset -------------------------- = ? v offset -------------------------- = = ---- - v vid ? 0.0125 ----------------- - 1.5 + ?? ?? =
isl6566 fn9178 rev 4.00 page 17 of 30 mar 9, 2006 advanced adaptive zero shoot-through deadtime control (patent pending) the integrated drive rs incorporate a unique adaptive deadtime control technique to minimize deadtime, resulting in high efficiency from the reduced fr eewheeling time of the lower mosfet body-diode conduction, and to prevent the upper and lower mosfets from conducting simultaneously. this is accomplished by ensuring eith er rising gate turns on its mosfet with minimum and sufficient delay after the other has turned off. during turn-off of t he lower mosfet, the phase voltage is monitored until it reaches a - 0.3v/+0.8v trip point for a forward/reverse current, at whi ch time the ugate is released to rise. an auto-zero comparator is used to correct the r ds(on) drop in the phase voltage prev enting false detection of the -0.3v phase level during r ds(on conduction period. in the case of zero current, the ugate is re leased after 35ns delay of the lgate dropping below 0.5v. dur ing the phase detection, the disturbance of lgate falling tr ansition on the phase node is blanked out to prevent false ly tripping. on ce the phase is high, the advanced adaptive shoo t-through circuitry monitors the phase and ugate voltages during a pwm falling edge and the subsequent ugate turn-off . if either the ugate falls to less than 1.75v above the ph ase or the phase falls to less than +0.8v, the lgate is released to turn on. internal bootstrap device all three integrated drivers f eature an internal bootstrap schottky diode. simply adding an external capacitor across the boot and phase pins compl etes the bootst rap circuit. the bootstrap function is als o designed to prevent the bootstrap capacitor from ove rcharging due to the large negative swing at the phase node. this reduces voltage stress on the boot to phase pins. the bootstrap capacitor must have a maximum voltage rating above pvcc + 5v and its capacit ance value can be chosen from the fo llowing equation: where q g1 is the amount of gate charge per upper mosfet at v gs1 gate-source voltage and n q1 is the number of control mosfets. the ? v boot_cap term is defined as the allowable droop in the ra il of the upper gate drive. gate drive voltage versatility the isl6566 provides the us er flexibility in choosing the gate drive voltage for efficien cy optimization. the controller ties the upper and lower drive rails together. simply applying a voltage from 5v u p to 12v on pvcc s ets both gate drive rail voltages simultaneously. initialization prior to initializat ion, proper conditions must exist on the enll, vcc, pvcc and the vid pins. when the conditions are met, the controller begins soft-start. once the output voltage is within the proper window of operation, the controller asserts pgood. enable and disable while in shutdown mode, the pwm outputs are held in a high-impedance state. this forces the drivers to short gate- to-source of the upper and lo wer mosfets to assure the mosfets remain off. the following input conditions must be met before the isl6566 is rel eased from this shutdown mode. 1. the bias voltage applied at vcc must reach the internal power-on reset (por) risi ng threshold. once this threshold is reached, proper operation of a ll aspects of the isl6566 is guaranteed. hyst eresis between the rising and falling thresholds assure that once enabled, the isl6566 will not inadvertently turn off unless the bias voltage drops substantially (see electrical specifications ). c boot_cap q gate ? v boot_cap -------------------------------------- ? q gate q g1 pvcc ? v gs1 ----------------------------------- - n q1 ? = (eq. 12) 50nc 20nc figure 10. bootstrap capacitance vs boot ripple voltage ? v boot_cap (v) c boot_cap ( f) 1.6 1.4 1.2 1. 0.8 0.6 0.4 0.2 0.0 0.3 0.0 0.1 0.2 0.4 0.5 0.6 0.9 0.7 0.8 1.0 q gate = 100nc
isl6566 fn9178 rev 4.00 page 18 of 30 mar 9, 2006 2. the voltage on enll mus t be above 0.66v. the enll input allows for power sequencing between the controller bias voltage and another voltage rail. the enable comparator holds the isl 6566 in shutdown until the voltage at enll rises ab ove 0.66v. the enable comparator has 60mv of hyst eresis to prev ent bounce. 3. the driver bias voltage appl ied at the pvcc pins must reach the internal power-on reset (por) rising threshold. in order for the isl6566 to begin operation, pvcc1 is the only pin that is required to have a voltage applied that exceeds por. however, fo r 2 or 3-phase operation pvcc2 and pvcc3 must also exceed the por threshold. hysteresis betwe en the rising and falling thresholds assure that once enabled, the isl6566 will not inadvertently turn off unless the pvcc bias voltage drops substantially (see electrical specifications ). 4. the vid code must not be 111111 or 111110 in vrm10 mode or 11111 in amd hammer or vrm9 modes. these codes signal the cont roller that no load is present. the controller will enter shut-down mode after receiving either of these codes and will execute soft-start upon receiving any other code. these codes can be used to enable or disable the controller but i t is not recommended. after receiving one of these codes, the controller executes a 2-cycle delay before ch anging the overvolt age trip level to the shut-down level and disabling pwm. overvoltage shutdown cannot be reset usi ng one of these codes. when each of these conditions is true, the controller immediately begins the soft-start sequence. soft-start the soft-start function allows the converter to bring up the output voltage in a controlled fashion, resulting in a linear ramp-up. following a delay of 16 ph ase clock cycles between enabling the chip and the start of the ramp, the output voltage progresses at a fixed rate of 12.5mv per each 16 phase clock cycles. thus, the soft-start period (n ot including the 16 phase clock cycle delay) up to a given voltage, v dac , can be approximated by the following equation where v dac is the dac-set vid voltage, and f s is the switching frequency. the isl6566 also has the abilit y to start up into a pre- charged output, without c ausing any unnecessary disturbance. the fb pin is mon itored during soft-start, and should it be higher than the equivalent internal ramping reference voltage, the output drives hold both mosfets off. once the internal ramping re ference exceeds the fb pin potential, the output drives are enabled, allowing the output to ramp from the pre-charged le vel to the final level dictated by the dac setting. should the output be pre-charged to a level exceeding the dac sett ing, the output drives are enabled at the end of the soft -start period, leading to an abrupt correction in the output voltage down to the dac-set level. figure 11. power sequencing using threshold- sensitive enable (enll) function - + 0.66v external circuit isl6566 internal circuit enll +12v por circuit 10.7k ? 1.40k ? enable comparator soft-start and fault logic vcc pvcc1 t ss v dac 1280 ? f s --------------------------------- = (eq. 13) figure 12. soft-start waveforms for isl6566-based multi-phase converter enll (5v/div) v out (0.5v/div) gnd> t1 gnd> t2 t3 output precharged below dac level output precharged above dac level
isl6566 fn9178 rev 4.00 page 19 of 30 mar 9, 2006 fault monitoring and protection the isl6566 actively monitors ou tput voltage and current to detect fault conditions. faul t monitors trigger protective measures to prevent damage to a microprocessor load. one common power good indicator is provided for linking to external system monitors. t he schematic in figure 13 outlines the interaction betw een the fault monitors and the power good signal. power good signal the power good pin (pgood) is an open-drain logic output that transitions high when the converter is operating after soft-start. pgood pulls low dur ing shutdown and releases high after a successful soft-st art. pgood transitions low when an undervoltage, overvoltage, or overcurrent condition is detected or when the controlle r is disabled by a reset from enll, por, or one of the no- cpu vid codes. if after an undervoltage or overvoltage event occurs the output returns to within under and overvolta ge limits, pgood will return high. undervoltage detection the undervoltage threshold is set at 82% of the vid code. when the output vo ltage (vsen-rgnd) is below the undervoltage threshold, pgood gets pulled low. no other action is taken by the controlle r. pgood will return high if the output voltage rises a bove 85% of the vid code. overvoltage protection the isl6566 constantly monito rs the difference between the vsen and rgnd voltages to detect if an overvoltage event occurs. during soft-start, wh ile the dac is ramping up, the overvoltage trip level is the higher of dac plus 150mv or a fixed voltage, v ovp . the fixed voltage, v ovp , is 1.67v when running in amd hammer, or vrm10 modes, and 1.97v for vrm9 mode. upon successful soft -start, the over voltage trip level is only dac plus 150mv. ovp releases 50mv below its trip point if it was dac plus 150mv that tripped it, and releases 100mv below its trip point if it was the fixed voltage , v ovp , that tripped it. actions are taken by the isl6566 to protect the microprocessor load when an overvoltage condition occurs, unt il the output voltage falls back within se t limits. at the inception of an overvoltage event, all lgate signals are commanded high, and the pg ood signal is driven low. this causes the controller to turn on the lower mosfets and pull the output voltage bel ow a level that might cause damage to the load. the lgate outputs remain high until vdiff falls to within the over voltage limits explained above. the isl6566 will contin ue to protect the lo ad in this fashion as long as the overvol tage condition recurs. once an overvoltage conditi on ends the isl6566 continues normal operation and pgood returns high. pre-por overvoltage protection prior to pvcc and vcc exc eeding their por levels, the isl6566 is designed to protect the load from any overvoltage events that may occur. this is accomplished by means of an internal 10k ? resistor tied from phase to lgate, which turns on the lower mosfet to control the output voltage until the overvoltage event ceases or the input power supply cuts off. for complete prote ction, the low side mosfet should have a gate thresho ld well below the maximum voltage rating of the l oad/microprocessor. in the event that during norma l operation the pvcc or vcc voltage falls back below the por threshold, the pre-por overvoltage protection circuit ry reactivates to protect from any more pre-por overvoltage events. open sense line protection in the case th at either of the remot e sense lines, vsen or gnd, become open, the isl6566 is designed to detect this and shut down the controller . this event is detected by monitoring the voltage on the iref pin, which is a local version of v out sensed at the output s of the inductors. figure 13. power good and protection circuitry - + vid + 150mv vsen - + 0.82 x dac ov uv pgood soft-start, fault and control logic - + oc - + isen iref isum icomp ocset r ocset + - v droop v ocset + - v ovp 100ua isl6566 internal circuitry - + rgnd x1 - + +1v vdiff
isl6566 fn9178 rev 4.00 page 20 of 30 mar 9, 2006 if vsen or rgnd become opened, vdiff falls, causing the duty cycle to increase and the output voltage on iref to increase. if the voltage on i ref exceeds vdiff+1v, the controller will shut down. once the voltage on iref falls below vdiff+1v, the isl6566 will restart at the beginning of soft-start. overcurrent protection the isl6566 detects overcurrent events by comparing the droop voltage, v droop , to the ocset voltage, v ocset , as shown in figure 13. the droop voltage, set by the external current sensing circuitry, is proportional to the output curren t as shown in equation 7. a constant 100 ? a flows through r ocset , creating the ocset vol tage. when the droop voltage exceeds the ocset v oltage, the overcurrent protection circuitry activates . since the droop voltage is proportional to the out put current, the overcurrent trip level, i max , can be set by selecting the proper value for r ocset , as shown in equation 14. once the output curre nt exceeds the overcurrent trip level, v droop will exceed v ocset , and a comparator will trigger the converter to begin overcurrent p rotection procedures. at the beginning of overcurrent shutdow n, the controller turns off bot h upper and lower mosfets. the system rem ains in this state for a period of 4096 switching cycles. if th e controller is sti ll enabled at the end of this wait period, it will attempt a soft- start (as shown in figure 14). if the fault remains, the trip-retry c ycles will continue indefinitely until ei ther the controller is disab led or the fault is cleared. note that the energy deliv ered during tri p- retry cycling is much less than during full-load operation, so there is no th ermal hazard. general design guide this design guide is intended to provide a high-level explanation of the steps necessa ry to create a multi-phase power converter. it is assumed that the reader is familiar with many of the basic skills and t echniques referenced below. in addition to this guide, inters il provides complete reference designs that include schematics, bills of materials, and exampl e board layouts for all common m icroprocessor applications. power stages the first step in designing a multi-phase converter is to determine the number of phases. this determination depends heavily on the cost anal ysis which in turn depends on system constraints that differ from one design to the next. principally, the designer will be concerned with whether components can be mounted on both sides of the circuit board, whether through-hole components are permitted, the total board space available for power-supply circuitry, and the maximum amount of load current. generally speaking, the most economical soluti ons are those in which each phase handles betwe en 25 and 30a. all surface-mount designs will tend toward the lower end of this current range. if through-hole mosfets and inductors can be used, higher per-phase currents are possi ble. in cases where board space is the limiting constrai nt, current can be pushed as high as 40a per phase, but these designs require heat sinks and forced air to cool the mosfets, inductors and heat- dissipating surfaces. mosfets the choice of mosfets depends on the current each mosfet will be required to conduct, the switching frequency, the capability of the mosfets to dissipate heat, and the availability and nature o f heat sinking and air flow. lower mosfet power calculation the calculation for power lo ss in the lower mosfet is simple, since virtually all of the loss in the lower mosfet is due to current conducted th rough the channel resistance (r ds(on) ). in equation 15, i m is the maximum continuous output current, i pp is the peak-to-peak i nductor current (see equation 1), and d is the duty cycle (v out /v in ). an additional term can be ad ded to the lower-mosfet loss equation to account for additional loss accrued during the dead time when inductor current is flowing through the lower-mosfet body diode. this term is dependent on the diode forward voltage at i m , v d(on) , the switching frequency, f s , and the length of dead times, t d1 and t d2 , at the beginning and the end of the lower-mosfet conduction interval respectively. the total maximum power dissipated in each lower mosfet is approximated by the summation of p low,1 and p low,2 . r ocset i max r comp dcr ?? 100 ? r s ? ---------------------------------------------------------- = (eq. 14) 0a 0v 2ms/div output current, 50a/div figure 14. overcurrent behavior in hiccup mode f sw = 500khz output voltage, 500mv/div p low 1 ? r ds on ?? i m n ----- - ?? ?? ?? 2 1d C ?? i lpp , 2 1d C ?? 12 -------------------------------- + = (eq. 15) p low 2 ? v don ?? f s i m n ----- - i pp 2 -------- - + ?? ?? t d1 i m n ----- - i pp 2 -------- - C ?? ?? ?? t d2 + = (eq. 16)
isl6566 fn9178 rev 4.00 page 21 of 30 mar 9, 2006 upper mosfet power calculation in addition to r ds(on) losses, a large portion of the upper- mosfet losses are due to cu rrents conducted across the input voltage (v in ) during switching. since a substantially higher portion of the uppe r-mosfet losses are dependent on switching frequency, the p ower calculation is more complex. upper mosfet los ses can be divided into separate components inv olving the upper-mosfet switching times, the lowe r-mosfet body-diode reverse- recovery charge, q rr , and the upper mosfet r ds(on) conduction loss. when the upper mosfet turns off, the lower mosfet does not conduct any portion of the inductor current until the voltage at the phase node falls below ground. once the lower mosfet begins conducti ng, the current in the upper mosfet falls to zero as the current in the lower mosfet ramps up to assume the full inductor current. in equation 17, the required time for t his commutation is t 1 and the approximated associated power loss is p up,1 . at turn on, the upper mosfet b egins to conduct and this transition occurs over a time t 2 . in equation 18, the approximate power loss is p up,2 . a third component involves the lower mosfet reverse- recovery charge, q rr . since the inductor current has fully commutated to the upper mos fet before the lower- mosfet body diode can recover all of q rr , it is conducted through the upper mosfet across vin. the power dissipated as a result is p up,3 . finally, the resistive part of t he upper mosfet is given in equation 20 as p up,4 . the total power dissipated by the upper mosfet at full load can now be approximated as the summation of the results from equations 17, 18, 19 and 20. since the power equations depend on mosfet p arameters, choosing the correct mosfets can be an it erative process involving repetitive solutions to the l oss equations for different mosfets and different switching frequencies. package power dissipation when choosing mosfets it is important to consider the amount of power being dissipa ted in the inte grated drivers located in the controller. sin ce there are a t otal of three drivers in the controller pack age, the total power dissipated by all three drivers mus t be less than the maximum allowable power dissipation for the qfn package. calculating the power dissipation in the drivers for a desired application is critical to ensure safe operation. exceeding the maximum allowable power dissipa tion level will push the ic beyond the maximum recomm ended operating junction temperature of 125 c. the maximum allowable ic power dissipation for the 6x6 qfn package is approximately 4w at room temperature. see layout considerations paragraph for thermal transfer improvement suggestions. when designing the isl6566 into an application, it is recommended that the followin g calculation is used to ensure safe operation at the desired frequency for the selected mosfets. the tota l gate drive po wer losses, p qg_tot , due to the gate char ge of mosfets and the integrated drivers internal circ uitry and their corresponding average driver current can be estimated with equations 21 and 22, respectively. in equations 21 and 22, p qg_q1 is the total upper gate drive power loss and p qg_q2 is the total lower gate drive power loss; the gate charge (q g1 and q g2 ) is defined at the particular gate to sourc e drive voltage pvcc in the corresponding mosfet data sheet; i q is the driver total quiescent current with no lo ad at both drive outputs; n q1 and n q2 are the number of upper and lower mosfets per phase, respectively; n phase is the number of active phases. the i q* vcc product is the qui escent power of the controller without capacitive load and is typically 75mw at 300khz. p up 1 , v in i m n ----- - i pp 2 -------- - + ?? ?? t 1 2 ---- ?? ?? ?? f s ? (eq. 17) p up 2 , v in i m n ----- - i pp 2 -------- - C ?? ?? t 2 2 ---- ?? ?? ?? f s ? (eq. 18) p up 2 , v in i m n ----- - i pp 2 -------- - C ?? ?? t 2 2 ---- ?? ?? ?? f s ? ? ? ???? ? ?? ?? i m n ----- - ?? ?? ?? 2 d i pp 2 12 --------- - + ? (eq. 20) figure 15. typical upper-gate drive turn-on path p qg_tot p qg_q1 p qg_q2 i q vcc ? ++ = (eq. 21) p qg_q1 3 2 -- - q g1 pvcc ? ? f sw ? n q1 ? n phase ? = p qg_q2 q g2 pvcc ? f sw ? n q2 n phase ? ? = i dr 3 2 -- - q g1 n ? q1 ? q g2 n q2 ? + ?? ?? n phase ? f sw i q + ? = (eq. 22) q1 d s g r gi1 r g1 boot r hi1 c ds c gs c gd r lo1 phase pvcc ugate
isl6566 fn9178 rev 4.00 page 22 of 30 mar 9, 2006 the total gate drive power losses are dissipated among the resistive components along t he transition path and in the bootstrap diode. the portion of t he total power dissipated in the controller itself is the power dissipated in the upper driv e path resistance, p dr_up , the lower drive path resistance, p dr_up , and in the boot strap diode, p boot . the rest of the power will be dissip ated by the external gate resistors (r g1 and r g2 ) and the internal g ate resistors (r gi1 and r gi2 ) of the mosfets. figures 15 and 16 show the typical upper and lower gate drives turn-on transition path. the total power dissipation in the controller itself, p dr , can be roughly estimated as: current balancing component selection the isl6566 senses the channel load current by sampling the voltage across the lower mosfet r ds(on) , as shown in figure 17. the isen pins ar e denoted isen1, isen2, and isen3. the resistors connected between these pins and the respective phase nodes dete rmine the gains in the channel- current balance loop. select values for these re sistors based on the room temperature r ds(on) of the lower mosfet s; the full-load operating current, i fl ; and the number of phases, n using equation 24. in certain circumsta nces, it may be neces sary to adjust the value of one or more isen resistors. when the components of one or more channels are inhibited from effectively dissipating their heat so that the affected channels run hotter than desired, choose new, smaller values of r isen for the affected phases (see the section entitled channel-current balance ). choose r isen,2 in proportion to the desired decrease in temperature rise in order to c ause proportionally less current to flow in the hotter phase. in equation 25, make sure that ? t 2 is the desired temperature rise above the ambient temperature, and ? t 1 is the measured temperature rise above the am bient temperature. while a single adjustment according to equation 25 is usually sufficient, it may occasio nally be necessary to adjust r isen two or more times to achie ve optimal thermal balance between all channels. load line regulation component selection (dcr current sensing) for accurate load line regulati on, the isl6566 senses the total output current by detect ing the voltage across the output inductor dcr of each ch annel (as described in the load line regulation section). as figure 18 illustrates, an r-c network is requir ed to accurately s ense the inductor dcr voltage and convert this information into a droop voltage, which is proportional to the total output current. choosing the components for this current sense network is a two step process. first, r comp and c comp must be chosen so that the time constant of this r comp -c comp network matches the time constant of the inductor l/dcr. figure 16. typical lower-gate drive turn-on path pvcc q2 d s g r gi2 r g2 r hi2 c ds c gs c gd r lo2 lgate p dr p dr_up p dr_low p boot i q vcc ? ?? +++ = (eq. 23) p dr_up r hi1 r hi1 r ext1 + -------------------------------------- r lo1 r lo1 r ext1 + ---------------------------------------- + ?? ?? ?? p qg_q1 3 --------------------- ? = p dr_low r hi2 r hi2 r ext2 + -------------------------------------- r lo2 r lo2 r ext2 + ---------------------------------------- + ?? ?? ?? p qg_q2 2 --------------------- ? = r ext1 r g1 r gi1 n q1 ------------- + = r ext2 r g2 r gi2 n q2 ------------- + = p boot p qg_q1 3 --------------------- = - isen(n) r isen v in channel n upper mosfet channel n lower mosfet - + i l r ds on ?? i l isl6566 r isen r ds on ?? 50 10 6 C ? ----------------------- i fl n ------- - = (eq. 24) r isen 2 , r isen ? t 2 ? t 1 ---------- = (eq. 25)
isl6566 fn9178 rev 4.00 page 23 of 30 mar 9, 2006 then the resistor r s must be chosen to set the current sense network gain, obtaining the desired full load droop voltage. follow the steps below to choose the component values for this r-c network. 1. choose an arbitrary value for c comp . the recommended value is 0.01 ? f. 2. plug the inductor l and dcr component values, and the values for c comp chosen in steps 1, into equation 26 to calculate the value for r comp . 3. use the new value for r comp obtained from equation 26, as well as the desired full load current, i fl , full load droop voltage, v droop , and inductor dcr in equation 27 to calculate the value for r s . due to errors in the inductan ce or dcr it may be necessary to adjust the value of r comp to match the ti me constants correctly. the effects of time constant mismatch can be seen in the form of droop overshoo t or undershoot during the initial load transient spike, as shown in figure 19. follow the steps below to ensure the r-c and inductor l/dcr time constants are matched accurately. 1. capture a transient event with the oscilloscope set to about l/dcr/2 (sec/div). for example, with l = 1 ? h and dcr = 1m ? , set the oscilloscope to 500 ? s/div. 2. record ? v1 and ? v2 as shown in figure 19. 3. select a new value, r comp,2 , for the time constant resistor based on the original value, r comp,1 , using the following equation. 4. replace r comp with the new value and check to see that the error is corrected. repeat the procedure if necessary. after choosing a new value for r comp , it will most likely be necessary to adjust the value of r s to obtain the desired full load droop voltage. use equation 27 to obtain the new value for r s . compensation the two opposing goals of c ompensating the voltage regulator are stability and speed. the load-line regulated con verter behaves in a similar manner to a peak current mode controller because the two poles at the output filter l-c r esonant frequency split with th e introduction of curre nt information into t he control loop. the final location of the se poles is determ ined by the system function, the gain of the current signal, a nd the value of the compensation components, r c and c c . since the system poles and zero are affected by the values of the components that are mean t to compensate them, the solution to the system equation becomes fairly complicated. r comp l dcr c comp ? --------------------------------------- = (eq. 26) r s i fl v droop ------------------------ - r comp dcr ?? = (eq. 27) figure 18. dcr sensing configuration - + icomp r s dcr l inductor c out i l 1 - + v l (s) dcr l inductor dcr l inductor phase1 phase2 phase3 i l 2 i l 3 r s r s r comp c comp isum iref isl6566 - + v droop i out (optional) 5 &203 ? r comp 1 ? v 1 ? v 2 ? ---------- ? = (eq. 28) figure 19. time constant mismatch behavior ? v 1 v out i tran ? v 2 ? i figure 20. compensation configuration for load-line regulated isl6566 circuit isl6566 comp c c r c r fb fb vdiff c 2 (optional)
isl6566 fn9178 rev 4.00 page 24 of 30 mar 9, 2006 fortunately, there i s a simple approximat ion that comes very close to an optimal s olution. treating th e system as though it were a voltage-mode regulator, by compensating the l-c poles and the esr zero of t he voltage mode approx imation, yields a solution that is alw ays stable with very c lose to ideal transie nt performance. select a target bandwidth f or the compensated system, f 0 . the target bandwidth must be lar ge enough to assure adequate transient performance, but smalle r than 1/3 of the per-channel switching frequency. the val ues of the compensation components depend on the relationships of f 0 to the l-c pole frequency and the esr zero f requency. for each of the following three, there is a sepa rate set of equations for the compensation components. in equations 29, l is the per-c hannel filter inductance divided by the number of active channel s; c is the sum total of all output capacitors; esr is the equivalent series resistance of the bulk output filter capacitance; and v pp is the peak-to-peak sawtooth signal amplitu de as described in the electrical specifications . once selected, the compensat ion values in equations 29 assure a stable converter with reasonable transient performance. in most cases, transient performance can be improved by making adjustments to r c . slowly increase the value of r c while observing the trans ient performance on an oscilloscope until no further improvement is noted. normally, c c will not need adjustm ent. keep the value of c c from equations 29 unless some per formance issue is noted. the optional capacitor c 2 , is sometimes needed to bypass noise away from the pwm comparator (see figure 20). keep a position available for c 2 , and be prepared to install a high- frequency capacitor of between 22pf and 150pf in case any leading edge jitter problem is noted. output filter design the output inductors and the output capacit or bank together to form a low-pass filter responsible for smoothing the pulsating voltage at the phase nodes. the output filter als o must provide the transient energy until the r egulator can respond. because i t has a low bandwidth compared to the switching frequency, the output filter limits the system transient r esponse. the output capacitors must supply or sink load current while the current i n the output inductor s increases or decreases to meet the demand. in high-speed converters, the output capacitor bank is usually the most costly (and often the largest) part of the circuit. ou tput filter design begins w ith minimizing the c ost of this part of t he circuit. the critical load para meters in choosing the output capacitors are the maximu m size of the load step, ? i, the load- current slew rate, di/dt, and the maximum allowable output- voltage deviation unde r transient loading, ? v max . capacitors are characterized according to their capacitance, esr, and esl (equivalent series inductance). at the beginning of the load tra nsient, the output capacitors supply all of the transient current. the output voltage will in itially deviate by an amount approximat ed by the voltage drop across the esl. as the load current increases, the voltage drop across the esr increases linearly until the load current reaches its f inal value. the capacitors selected mu st have sufficiently low esl and esr so that the total outpu t-voltage deviation is less than the allowable maximum. neglecti ng the contribution of inductor current and regulator response, the output voltage initially deviates by an amount the filter capacitor must have sufficient ly low esl and esr so that ? v < ? v max . most capacitor solutions rely on a mixture of high frequency capacitors with relati vely low capacitance in combination with bulk capacitors having high c apacitance but limited high- frequency performance. min imizing the esl of the high- frequency capacitors allows them to support the output voltage as the current increases. min imizing the esr of the bulk capacitors allows them to supply the increased current with les s output voltage deviation. the esr of the bulk capacitors a lso creates the majority of the output-voltage ripple. as the bul k capacitors sink and source the inductor ac ripple current (see interleaving and equation 2), a voltage develops across the bulk capacitor esr equal to i c,pp (esr). thus, once the output ca pacitors are selected, the maximum allowable ripple voltage, v pp(max) , determines the lower limit on the inductance. 1 2 ? lc ------------------- f 0 > r c r fb 2 ? f 0 v pp lc 0.66v in ----------------------------------- - = c c 0.66v in 2 ? v pp r fb f 0 ------------------------------------ = case 1: 1 2 ? lc ------------------- f 0 1 2 ? c esr ?? ----------------------------- - < ? r c r fb v pp 2 ? ?? 2 f 0 2 lc 0.66 v in -------------------------------------------- = c c 0.66v in 2 ? ?? 2 f 0 2 v pp r fb lc ------------------------------------------------------------- = case 2: (eq. 29) f 0 1 2 ? c esr ?? ----------------------------- - > r c r fb 2 ? f 0 v pp l 0.66 v in esr ?? ----------------------------------------- - = c c 0.66v in esr ?? c 2 ? v pp r fb f 0 l ------------------------------------------------- = case 3: ? v esl ?? di dt ---- - esr ??? i + ? (eq. 30) l esr ?? v in nv out C ?? ?? v out f s v in v pp max ?? ----------------------------------------------------------- - ? (eq. 31)
isl6566 fn9178 rev 4.00 page 25 of 30 mar 9, 2006 since the capacitors are supplyi ng a decreasing portion of the load current while the regulato r recovers from the transient, t he capacitor voltage becomes slig htly depleted. the output inductors must be capable of a ssuming the entire load current before the output voltage decreases more than ? v max . this places an upper limit on inductance. equation 32 gives the upper limit on l for the cases when the trailing edge of the current trans ient causes a greater output- voltage deviation than the leading edge. equation 33 addresses the leading edge. normally, the trailing edge dictate s the selection of l because duty cycles are usually less than 50%. nevertheless, both inequalities should be evaluated, and l should be selected b ased on the lower of the two results. in each equation, l is the per-cha nnel inductance, c is the total output capacitance, a nd n is the number o f active channels. switching frequency there are a number of variables to consider when choosing the switching frequency, as there ar e considerable effects on the upper mosfet loss calculation. t hese effects are outlined in mosfets , and they establish the up per limit for the switching frequency. the lower limit is esta blished by the requirement fo r fast transient response and sma ll output-voltage ripple as outlined in output filter design . choose the lowest switching frequency that allows the regul ator to meet the transient- response requirements. switching frequency is determi ned by the selection of the frequency-setting resistor, r t . figure 21 and equation 34 are provided to assist in select ing the correct value for r t . input capacitor selection the input capacitors are res ponsible for sourcing the ac component of the input curre nt flowing into the upper mosfets. their rms current capacity must be sufficient to handle the ac component of the current drawn by the upper mosfets which is related to duty cycle and th e number of active phases. for a three-phase design, use figure 22 to determine the input- capacitor rms current require ment set by the duty cycle, maximum sustained output current (i o ), and the ratio of the peak-to-peak inductor current (i l,pp ) to i o . select a bulk capacitor with a ripple current rating which will minimize the total number of input capacitor s required to support the rms current calculated. the voltage rating of the capacitors should also be at least 1.25 times gr eater than the maximum input voltage. figures 23 and 24 provide the same input rms current information for two-phase and single-phase designs respectively. use the same app roach for selecting the bulk capacitor type and number. l 2ncv o ??? ? i ?? 2 --------------------------------- ? v max ? i esr ? ?? C ? (eq. 32) l 1.25 ?? nc ?? ? i ?? 2 --------------------------------- - ? v max ? i esr ? ?? C v in v o C ?? ?? ? (eq. 33) r t 10 10.61 1.035 f s ?? log C ?? = (eq. 34) 10 100 1000 10 100 1000 10000 figure 21. r t vs switching frequency switching frequency (khz) r t (k ? ) figure 22. normalized input-capacitor rms current for 3-phase converter duty cycle (v in/ v o ) 00.4 1.0 0.2 0.6 0.8 input-capacitor current (i rms/ i o ) 0.3 0.1 0 0.2 i l,pp = 0 i l,pp = 0.25 i o i l,pp = 0.5 i o i l,pp = 0.75 i o figure 23. normalized input-capacitor rms current for 2-phase converter 0.3 0.1 0 0.2 input-capacitor current (i rms/ i o ) 00.4 1.0 0.2 0.6 0.8 duty cycle (v in/ v o ) i l,pp = 0 i l,pp = 0.5 i o i l,pp = 0.75 i o
isl6566 fn9178 rev 4.00 page 26 of 30 mar 9, 2006 low capacitance, high-frequency ceramic capacitors are needed in addition to the input bulk capacitors to suppress leading and falling edge voltage spikes. the spikes result from the high current slew rate prod uced by the upper mosfet turn on and off. select low esl ceramic capacitors and place one as close as possible to each upp er mosfet drain to minimize board parasitics and m aximize suppression. layout considerations mosfets switch very fast and efficiently. the speed with which the current transitions f rom one device to another causes voltage spikes across the interconnecting impedances and parasitic circuit element s. these voltage spikes can degrade efficiency, radiate nois e into the circuit and lead to device overvoltage stress. careful component selection, layout, and placement minimizes these voltage spikes. consider, as an example, the t urnoff transition of the upper pwm mosfet. prior to turnoff, the upper mosfet was carrying channel current. during the turnoff, current stops flowing in the upper mosfet a nd is picked up by the lower mosfet. any inductance in the switched current path generates a large voltage spike during the switching interval. careful component se lection, tight layout of the critical components, and short, wide ci rcuit traces minimize the magnitude of voltage spikes. there are two sets of crit ical components in a dc-dc converter using a isl6566 cont roller. the power components are the most critical because they switch lar ge amounts of energy. next are small signal components that connect to sensitive nodes or s upply critical bypassing current and signal coupling. the power components sh ould be placed first, which include the mosfets, input and output capacitors, and the inductors. it is important to have a symmetric al layout for each power train, preferably with the controller located equidistant from each. symmetrical layout allows heat to be dissipated equally across all three power trains. equidistant placement of the controller to the three power trains also he lps keep the gate drive traces equally short, resulting in equal t race impedances and similar drive capability of a ll sets of mosfets. when placing the mosfets try to keep the source of the upper fets and the drain of the lower fets as close as thermally possible. input bulk capacitors should be placed close to the drain of the upper fets and the source of the lower fets. locat e the output inductor s and output capacitors between the mosfets and the load. the high -frequency input and output decoupling capacitors (ceramic) should be placed as close as practicable to the decoupling target, making use of the shortes t connection paths to any internal planes, such as vias to gnd ne xt or on the capacitor solder pad. the critical small components in clude the bypass capacitors for vcc and pvcc, and many of the components surrounding the controller inc luding the feedback network and current sense components. locate the vcc/pvcc bypass capacitors as close to the isl6566 as possi ble. it is especially important to locate the components asso ciated with the feedback circuit close to their respective controller pins, since they belong to a high-impedance circuit loop, sens itive to emi pick-up. it is al so important to place the current sense components close to their respective pins on the isl6566, including r isen , r s , r comp , and c comp . a multi-layer printed circuit board is recomm ended. figure 25 shows the connections of the c ritical components for the converter. note that capacitors c xxin and c xxout could each represent numerous physical capacitors. dedicate one solid laye r, usually the one underneath the component side of the board, for a ground plane and make all critical component ground connections with vias to this layer. dedicat e another solid layer as a powe r plane and break this plane into smaller islands of common volta ge levels. keep the metal runs fr om the phase term inal to output inductors short. the power plane should support the input power and output power nodes. use copper filled polygons on the top and bottom circuit layers for th e phase nodes. use the remainin g printed circuit layers f or small signal wiring. routing ugate, lgate, and phase traces great attention should be paid to routing the ugate, lgate, and phase traces since they dri ve the power train mosfets using short, high current pulse s. it is important to size them as large and as short as possible to reduce their overall impedanc e and inductance. they should be sized to carry at least one ampere of current (0.02 to 0.05). going between layers with vias should also be avoided, b ut if so, use two vias for interconnection when possible. extra care should be given to the lgate traces in particular since keeping their impedance and inductance low helps to significantly reduce the possibility of shoot-through. it is al so important to route each channel s ugate and phase traces in as close proximity as possible to reduce their inductances. figure 24. normalized input-capacitor rms current for single-phase converter 00.4 1.0 0.2 0.6 0.8 duty cycle (v in /v o ) input-capacitor current (i rms /i o ) 0.6 0.2 0 0.4 i l,pp = 0 i l,pp = 0.5 i o i l,pp = 0.75 i o
isl6566 fn9178 rev 4.00 page 27 of 30 mar 9, 2006 thermal management for maximum thermal performanc e in high current, high switching frequency applicati ons, connecting the thermal gnd pad of the isl6566 to the grou nd plane with multiple vias is recommended. this heat spreading allows the part to achieve its full thermal potential. it is also recommended that the controller be placed in a direct path of airflow if possible to help thermally manage the part. suppressing mosfet gate leakage with vcc at ground potential, u gate is high impedance. in this state, any stray leakage has the potential to deliver char ge to the gate of the upper mosfet. if ugate receives sufficient charge to bias the d evice on, a low impedance path will be connected between the upper m osfet drain and phase. if this occurs and the input power supply is present and active, the system could see pot entially damaging current. worst-case leakage currents are on the orde r of pico-amps; therefore, a 10k ? resistor, connected from ugate to phase, is more than sufficient to bleed off any stra y leakage current . this resisto r will not affect the normal perfor mance of the driver or reduce its efficiency.
isl6566 fn9178 rev 4.00 page 28 of 30 mar 9, 2006 via connection to ground plane island on power plane layer island on circuit plane layer key figure 25. printed circuit board power planes and islands heavy trace on circuit plane layer vid3 vid4 pgood vid2 vid1 vid0 vdiff fb comp vcc isen1 isl6566 vid12.5 fs ofs ref +12v +12v +12v phase1 ugate1 boot1 lgate1 isen2 phase2 ugate2 boot2 lgate2 isen3 phase3 ugate3 boot3 lgate3 isum icomp iref load vsen rgnd ocset vrm10 +5v pvcc1 pvcc2 pvcc3 enll +12v gnd c boot1 c boot2 r isen1 r 1 c 1 c 2 r ofs r fb r isen2 r isen3 c boot3 c bin1 c bin2 (c hfout ) c bout (cf1) (cf2) c bin3 r t c ref locate close to ic locate near load; (minimize connection path) locate near switching transistors; (minimize connection path) (minimize connection path) (cf2) (cf2) c comp r comp r s r s r s r ocset
fn9178 rev 4.00 page 29 of 30 mar 9, 2006 isl6566 intersil products are manufactured, assembled and tested utilizing iso9001 quality systems as noted in the quality certifications found at www.intersil.com/en/suppor t/qualandreliability.html intersil products are sold by description on ly. intersil may modify the circuit design an d/or specifications of products at any time without notice, provided that such modification does not, in intersil's sole judgment, affect the form, fit or function of the product. accordingly, the reader is cautioned to verify that datasheets are current before placing orders. information fu rnished by intersil is believed to be accu rate and reliable. however, no responsib ility is assumed by intersil or its subsidiaries for its use; nor for any infrin gements of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of intersil or its subsidiaries. for information regarding intersil corporation and its products, see www.intersil.com for additional products, see www.intersil.com/en/products.html ? copyright intersil americas ll c 2004-2006. all rights reserved. all trademarks and registered trademarks are the property of their respective owners.
isl6566 fn9178 rev 4.00 page 30 of 30 mar 9, 2006 quad flat no-lead plastic package (qfn) micro lead frame pl astic package (mlfp) index d1/2 d1 d/2 d e1/2 e/2 e a 2x 0.15 b c 0.10 b a mc a n seating plane n 6 3 2 2 3 e 1 1 0.08 for odd terminal/side for even terminal/side c c section "c-c" nx b a1 c 2x c 0.15 0.15 2x b 0 ref. (nd-1)xe (ne-1)xe ref. 5 a1 4x p a c c 4x p b 2x a c 0.15 a2 a3 d2 d2 e2 e2/2 terminal tip side view top view 7 bottom view 7 5 c l c l e e e1 2 nx k nx b 8 nx l 8 8 9 area 9 4x 0.10 c / / 9 (datum b) (datum a) area index 6 area n 9 corner option 4x l1 l 10 l1 l 10 l40.6x6 40 lead quad flat no-lead plastic package (compliant to jedec mo-220vjjd-2 issue c) symbol millimeters notes min nominal max a 0.80 0.90 1.00 - a1 - - 0.05 - a2 - - 1.00 9 a3 0.20 ref 9 b 0.18 0.23 0.30 5, 8 d 6.00 bsc - d1 5.75 bsc 9 d2 3.95 4.10 4.25 7, 8 e 6.00 bsc - e1 5.75 bsc 9 e2 3.95 4.10 4.25 7, 8 e 0.50 bsc - k0.25 - - - l 0.30 0.40 0.50 8 l1 - - 0.15 10 n402 nd 10 3 ne 10 3 p- -0.609 ? --129 rev. 1 10/02 notes: 1. dimensioning and tolerancing conform to asme y14.5-1994. 2. n is the number of terminals. 3. nd and ne refer to the number of terminals on each d and e. 4. all dimensions are in millimeters. angles are in degrees. 5. dimension b applies to the meta llized terminal and is measured between 0.15mm and 0.30mm from the terminal tip. 6. the configuration of the pin #1 identifier is optional, but must be located within the zone indicated. the pin #1 identifier may be either a mold or mark feature. 7. dimensions d2 and e2 are fo r the exposed pads which provide improved electrical and thermal performance. 8. nominal dimensions are provided to assist with pcb land pattern design efforts, see intersil technical brief tb389. 9. features and dimensions a2, a3, d1, e1, p & ? are present when anvil singulation method is used and not present for saw singulation. 10. depending on the method of lead termination at the edge of the package, a maximum 0.15mm pull back (l1) maybe present. l minus l1 to be equal to or greater than 0.3mm.

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