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nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation sp7662 features 4.75v to 22v input voltage range using single supply 3v to 22v input voltage range using dual supply % 0.8v reference 2a output capability current limiting using inductor dcr built in low r ds(on) power switches 300 khz fixed frequency operation over temperature protection short circuit protection with auto-restart wide bw amp allows type ii or iii compensation programmable soft start fast transient response high effciency: greater than 95% possible nonsynchronous start-up into a pre-charged output available in rohs compliant, lead free packaging: small 7mm x 4mm dfn u.s. patent #6,922,04 wide input voltage range 12a, 300khz, buck regulator the sp7662 is a synchronous step-down switching regulator optimized for high effciency. the part is designed for use with a single 4.75v to 22v single supply or 3v to 22v input if an external vcc is provided. the sp7662 pro - vides a fully integrated buck regulator solution using a fxed 300 khz frequency, pwm voltage mode architecture. protection features include uvlo, thermal shutdown, output current limit and short circuit protection. the sp7662 is available in the space saving dfn package . typical application circuit description power blox tm sp7662 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 2 2 23 24 25 26 bottom view heatsink pad 1 connect to lx heatsink pad 2 connect to gnd heatsink pad 3 connect to v in p gnd p gnd gnd v fb comp uv in swn v in lx lx lx lx v cc bst lx lx lx dfn package 7mm x 4mm (option 2) p gnd vinp ss isn isp p gnd gnd gnd gnd pin 27 pin 28 pin 29 12v sd101aws 3.30v, 0-12a gnd c5 100uf vout u1 sp7662 rs1 cz2 10nf c9 6.8nf rs2 1 ? cp1 100pf rbst 5.1 ? c1 22uf c3 22uf r1 10k ? cbst 22nf r8 np cs1 2.2nf cs2 2.2nf c2 22uf gnd cvcc 4.7uf rz3 453 ? r3 5.11k ? r9 np dbst rz2 4020 ? l1, sc5018-2r7m 2.7uh, 4.1m ? r2 3160 ? vin c6 100uf css 47nf r4 5.11k ? cz3 2.2nf c4 .1uf cf1 100pf isp isn isn lx lx isp nc 1 ? pgnd 1 pgnd 2 pgnd 3 pgnd 4 gnd 5 vfb 6 comp 7 ss 8 gnd 9 isn 10 isp 11 swn 12 vinp 13 lx 14 lx 15 lx 16 bst 17 vin 18 gnd 19 gnd 20 uvin 21 vcc 22 lx 23 lx 24 lx 25 lx 26 swn pad 27 gnd pad 28 vin pad 29
2 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation electrical specifications specifcations are for t amb = t j = 25c, and those denoted by ? apply over the full operating range, -40c< tj< 25c. unless otherwise specifed: 4.5v < vcc < 5.5v, 3v < v in < 22v, bst = lx + 5v, uvin = 3v, cvcc = f, c comp = 0. f, css = 50nf. v cc ...................................................................................................7v v in .................................................................................................25v bst ................................................................................................ 30v lx-bst ............................................................................... -0.3v to 7v lx ........................................................................................ -v to 30v all other pins .......................................................... -0.3v to v cc + 0.3v storage temperature ................................................... -65c to 50c power dissipation ........................................ internally limited via otp lead temperature (soldering, 0 sec) ....................................... 300c esd rating ........................................................................... 2kv hbm thermal resistance jc ............................................................ 5c/w absolute maximum ratings these are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifcations below is not implied. exposure to absolute maximum rating conditions for extended periods of time may affect reliability. parameter min typ max units ? conditions quiescent current v in supply current (no switching) .5 3.0 ma ? v fb = 0.9v v in supply current (switching) 8 20 ma bst supply current (no switching) 0.2 0.4 ma ? v fb = 0.9v bst supply current (switching) 3 6 ma protection: uvlo vcc uvlo start threshold 4.00 4.25 4.50 v ? vcc uvlo hysteresis 00 200 300 mv ? uvin start threshold 2.30 2.50 2.65 v ? uvin hysteresis 200 300 400 mv ? uvin input current .0 a ? uvin=3.0v error amplifier reference error amplifer reference 0.792 0.800 0.808 v 2x gain confg., measure v fb ; vcc=5v error amplifer reference over line 0.784 0.800 0.86 v ? comp sink current 70 50 230 a ? v fb =0.9v, comp=0.9v comp source current -230 -50 -70 a ? v fb =0.9v, comp=0.9v v fb input bias current 50 200 na ? v fb =0.8v comp clamp 3.2 3.5 3.8 v v fb =0.7v, t a =25 c comp clamp temp. coeffcient -2.0 mv/ c vcc linear r egulator vcc output voltage 4.7 5.0 5.3 v ? v in = 6 to 23v, i load = 0ma to 30ma 4.5 4.73 ? v in = 5v, 20ma dropout voltage 250 500 750 mv ? vin-vout = dropout voltage when vcc regulated drops by 2%. ivcc = 30ma.
3 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation electrical specifications specifcations are for t amb = t j = 25c, and those denoted by ? apply over the full operating range, -40c< tj< 25c. unless otherwise specifed: 4.5v < vcc < 5.5v, 3v < v in < 22v, bst = lx + 5v, uvin = 3v, cvcc = f, c comp = 0. f, css = 50nf. parameter min typ max units ? conditions control loop: pwm comparator, ramp & loop delay path ramp amplitude 0.80 .00 .20 v ? ramp offset .7 2.0 2.3 v ? ramp offset temperature coeffcient -2 mv/ c gh minimum pulse width 50 80 ns ? maximum controllable duty ratio 92 97 % ? maximum duty ratio 00 % ? valid for 20 cycles internal oscillator ratio 255 300 345 kh z ? timers: softstart ss charge current: -6 -0 -4.0 a ? ss discharge current: .0 2.0 3.0 ma ? fault present, ss=0.2v protection: short circuit, overcurrent & thermal short circuit threshold voltage 0.20 0.25 0.30 v ? hiccup timeout 70 220 270 ms ? v fb =0.5v overcurrent threshold voltage 54 60 66 mv measured isp - isn isp, isn common mode range 0 3.6 v thermal shutdown temperature 35 45 55 c guaranteed by design thermal recovery temperature 35 c thermal hysteresis 0 c output: power stage high side switch r dson 6.8 20.5 m? v gs =4.5v; i drain =5a; t amb =25c synchronous low side switch r dson 6.8 8.5 m? v gs =4.5v; i drain =5a; t amb =25c maximum output current 2 a ?
4 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation controller block diagram f a u l t 0 . 1 v 0 . 2 5 v s o f t s t a r t i n p u t 1 3 5 o c o f f 1 4 5 o c o n 5 0 k 1 4 0 k 4 . 0 5 v o f f 4 . 2 5 v o n f a u l t r f a u l t v c c g n d c o m p a r a t o r a s y n c . s t a r t u p 1 . 6 v s s g l h o l d o f f 300 k h z c l k c l o c k p u l s e g e n e r a t o r q s r e s e t d o m i n a n t q p w m s y n c h r o n o u s d r i v e r p g n d b s t 2 . 8 v 1 . 3 v r a m p = 1 v v p o s t h e r m a l a n d o v e r c u r r e n t p r o t e c t i o n u v l o c o m p a r a t o r s v c c u v l o h i c c u p f a u l t r e f o k c o u n t e r c l r c l k i s p i s n 6 0 m v o v e r c u r r e n t d e t e c t i o n d e t e c t i o n v f b i n t s h o r t c i r c u i t 2 0 0 m s d e l a y q d o m i n a n t r s s e t s h u t d o w n t h e r m a l v i n r e f o k c o r e 0 . 8 v u v i n v i n u v l o 2 . 5 0 v o n 2 . 2 0 v o f f r e g u l a t o r l i n e a r 5 v r e f e r e n c e p o w e r f a u l t v c c p o s r e f f a u l t v c c s s 1 0 u a v c c v f b i n t v f b g l p w m l o o p c o m p v p o s g m g m e r r o r a m p l i f i e r g h s w n note: the sp7662 uses the sipex pwm controller sp6133.
5 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation pin description pin # pin name description -4 pgnd ground connection for the synchronous rectifer. 5, 9, 9, 20 gnd ground pin. the control circuitry of the ic and lower power driver are referenced to this pin. return separately from other ground traces to the (-) terminal of c out . 6 vfb feedback voltage and short circuit detection pin. it is the inverting input of the error amplifer and serves as the output voltage feedback point for the buck converter. the output voltage is sensed and can be adjusted through an external resistor divider. whenever vfb drops 0.25v below the positive reference, a short circuit fault is detected and the ic enters hiccup mode. 7 comp output of the error amplifer. it is internally connected to the inverting input of the pwm comparator. an optimal flter combination is chosen and connected to this pin and either ground or vfb to stabilize the voltage mode loop. 8 ss soft start. connect an external capacitor between ss and gnd to set the soft start rate based on the 0a source current. the ss pin is held low via a ma (min) current during all fault conditions. 0 isn current sense negative input. rail-to-rail input for overcurrent detection. isp current sense positive input. rail-to-rail input for overcurrent detection. 2 swn lower supply rail for the gh high-side gate driver. connect this pin to the switching node as close as possible to pins 23- 27. do not connect this pin to pins 4 C 6. 3 vinp input connection to the high side n-channel mosfet. 4-6, 23-26 lx connect an inductor between this pin and v out . 7 bst high side driver supply pin. connect bst to the external boost diode and capacitor as shown in the typical application circuit on page . the high side driver is connected between bst pin and swn pin. 8 vin v in connection for internal ldo and pwm controller. 2 uvin uvlo input for v in voltage. connect a resistor divider between v in and uvin to set minimum operating voltage. use resistor values below 20k? to override internal resistor divider. 22 vcc output of internal regulator. may be exterinally biased if vin < 5v. sp7662 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 2 2 23 24 25 26 bottom view heatsink pad 1 connect to lx heatsink pad 2 connect to gnd heatsink pad 3 connect to v in p gnd p gnd gnd v fb comp uv in swn v in lx lx lx lx v cc bst lx lx lx dfn package 7mm x 4mm (option 2) p gnd vinp ss isn isp p gnd gnd gnd gnd pin 27 pin 28 pin 29
6 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation theory of operation general overview the sp7662 is a fxed frequency, volt - age mode, synchronous pwm regulator optimized for high effciency. the part has been specifcally designed for single supply operation from a 5v to 22v input. the heart of the sp7662 is a wide bandwidth transconductance amplifer designed to ac - commodate type ii and type iii compensa - tion schemes. a precision 0.8v reference, present on the positive terminal of the error amplifer, permits the programming of the output voltage down to 0.8v via the vfb pin. the output of the error amplifer, comp, is compared to a . v peak-to-peak ramp, which is responsible for trailing edge pwm control. this voltage ramp and pwm control logic are governed by the internal oscillator that accurately sets the pwm frequency to 300khz. the sp7662 contains two unique control features that are very powerful in distributed applications. first, nonsynchronous driver control is enabled during startup, to prohibit the low side switch from pulling down the output until the high side switch has at - tempted to turn on. second, a 00% duty cycle timeout ensures that the low side switch is periodically enhanced during extended periods at 00% duty cycle. this guaran - tees the synchronized refreshing of the bst capacitor during very large duty ratios. the sp7662 also contains a number of valu - able protection features. programmable v in uvlo allows the user to set the exact value at which the conversion voltage can safely begin down-conversion, and an internal v cc uvlo which ensures that the controller itself has enough voltage to properly operate. other protection features include thermal shutdown and short-circuit detection. in the event that either a thermal, short-circuit, or uvlo fault is detected, the sp7662 is forced into an idle state where the output drivers are held off for a fnite period before a restart is attempted. soft start soft start is achieved when a power con - verter ramps up the output voltage while controlling the magnitude of the input sup - ply source current. in a modern step down converter, ramping up the positive terminal of the error amplifer controls soft start. as a result, excess source current can be defned as the current required to charge the output capacitor. i vin = c out ? ( ? v out / ? t soft - st a rt ) the sp7662 provides the user with the op - tion to program the soft start rate by tying a capacitor from the ss pin to gnd. the selection of this capacitor is based on the 0 a pull up current present at the ss pin and the 0.8v reference voltage. therefore, the excess source can be redefned as: i vin = c out ? [ ? v out ? 0a / (c ss ? 0.8v) ] under voltage lock out (uvlo) the sp7662 has two separate uvlo com - parators to monitor the bias (vcc) and input (v i n ) voltages independently. the vcc uvlo is internally set to 4.25v. the v in uvlo is programmable through uv i n pin. when uvin pin is greater than 2.5v the sp7662 is permitted to start up pending the removal of all other faults. a pair of internal resistors is connected to uvin as shown in the fgure below. sp7662 r4 r5 + - 140k? 50k? 2.5v on 2.2v off gnd uvin vin internal and external bias of uvin
7 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation theory of operation therefore without external biasing the v in start threshold is 9.5v. a small capacitor may be required between uvin and gnd to flter out noise. for applications with v in of 5v or 3.3v, connect uvin directly to v in . to program the v in start threshold, use a pair of external resistors as shown. if external resistors are an order of magnitude smaller than internal resistors, then the v in start threshold is given by: v in (start) = 2.5 ? (r4+r5)/r5 for example, if it is required to have a v in start threshold of 7v, then let r5 = 5k? and using the v in start threshold equation we get r4 = 9.09k?. thermal and short-circuit protection because the sp7662 is designed to drive large output current, there is a chance that the power converter will become too hot. there - fore, an internal thermal shutdown ( 45c) has been included to prevent the ic from malfunctioning at extreme temperatures. a short-circuit detection comparator has also been included in the sp7662 to protect against an accidental short at the output of the power converter. this comparator con - stantly monitors the positive and negative terminals of the error amplifer, and if the v fb pin falls more than 250mv (typical) below the positive reference, a short-circuit fault is set. because the ss pin overrides the internal 0.8v reference during soft start, the sp7662 is capable of detecting short-circuit faults throughout the duration of soft start as well as in regular operation. over-current protection the over-current protection feature can only be used on output voltages 3.3 volts. it is limited by the common mode rating of the op-amp used to sense the voltage across the inductor. over-current is de - tected by monitoring a differential voltage across the output inductor as shown in the next fgure. isn sp7662 swn isp v out l = 2.7uh, dcr = 4.1m? rs 5.11k? rs2 5.11k? cs 0.uf csp 6.8n f over-current detection circuit inputs to an over-current detection com - parator, set to trigger at 60 mv nominal, are connected to the inductor as shown. since the average voltage sensed by the com - parator is equal to the product of inductor current and inductor dc resistance (dcr), then i max = 60mv / dcr. solving this equa - tion for the specifc inductor in circuit 1, i max = 4.6a. when i max is reached, a 220 ms time-out is initiated, during which top and bottom drivers are turned off. following the time-out, a restart is attempted. if the fault condition persists, then the time-out is re - peated (referred to as hiccup). increasing the current l imi t if it is desired to set i max > {60mv / dcr} (in this case larger than 4.6a), then a resistor r s3 should be added as shown in the next fgure. r s3 forms a resistor divider and re - duces the voltage seen by the comparator. since: 60mv ( i max ? dcr) r s3 = {r s + r s2 + r s3 }
8 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation solving for rs3 we get: r s3 = [60mv ? (r s1 + r s2 )] [( i max ? dcr) C 60mv] as an example: if desired i max is 7a, then r s3 = 63.4k . rs3 63.4k? csp 6.8nf swn isp isn sp7662 cs 0.uf rs2 5.11k? rs 5.11k? l = 2.7uh, dcr = 4.1m? v ou t over-current detection circuit for i max > 60mv / dcr decreasing the current limit if it is required to set i max < {60mv / dcr , a resistor is added as shown in the follow - ing fgure. rs3 increases the net voltage detected by the current-sense comparator. voltage at the positive and negative terminal of comparator is given by: vsp = v out + ( i max ? dcr) vsn = v out ? { r s3 / (r s2 +r s3 ) } since the comparator is triggered at 60mv: vsp-vsn = 60 mv combining the above equations and solv - ing for r s3 : r s3 = r s2 ? [ v out - 60mv + ( i max ? dcr) ] 60mv - ( i max ? dcr) as an example: for i ma x of 2a and v o ut of 3.3v, calculated r s3 is 1.5m?. csp 6.8nf isn sp7662 swn isp cs 0.uf rs2 5.11k? rs 5.11k? v out l = 2.7uh, dcr = 4.m ? rs3 1.5m? over-current detection circuit for i max < {60mv / dcr} handling of faults upon the detection of power (uvlo), ther - mal, or short-circuit faults, the sp7662 is forced into an idle state where the ss and comp pins are pulled low and both switches are held off. in the event of uvlo fault, the sp7662 remains in this idle state until the uvlo fault is removed. upon the detection of a thermal or short-circuit fault, an internal 200ms timer is activated. in the event of a short-circuit fault, a restart is attempted im - mediately after the 200ms timeout expires. whereas, when a thermal fault is detected the 200ms delay continuously recycles and a restart cannot be attempted until the thermal fault is removed and the timer expires. theory of operation
9 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation error amplifer and voltage loop the heart of the sp7662 voltage error loop is a high performance, wide bandwidth transconductance amplifier. because of the amplifers current limited (+/-150a) transconductance, there are many ways to compensate the voltage loop or to control the comp pin externally. if a simple, single-pole, single-zero response is desired, then com - pensation can be as simple as an rc circuit to ground. if a more complex compensation is required, then the amplifer has enough bandwidth (45 at 4 mhz), and enough gain (60db) to run type iii compensation schemes with adequate gain and phase margins at crossover frequencies greater than 50khz. the common mode output of the error am - plifer is 0.9v to 2.2v. therefore, the pwm voltage ramp has been set between . v and 2.2v to ensure proper 0% to 00% duty cycle capability. the voltage loop also includes two other very important features. one is a nonsynchronous startup mode. basically, the synchronous rectifer cannot turn on unless the high side switch has attempted to turn on or the ss pin has exceeded .7v. this feature prevents the controller from dragging down the output voltage during startup or in fault modes. gh v oltage gl v oltage v(v in ) 0v -0v -v(diode) v v(v in )+v(v cc ) bst v oltage v(v cc ) tim e sw n v oltage v bst v sw n v(v cc) the second feature is a 00% duty cycle timeout that ensures synchronized refresh - ing of the bst capacitor at very high duty ratios. in the event that the high side nfet is on for 20 continuous clock cycles, a reset is given to the pwm fip fop half way through the 2 st cycle. this forces gl to rise for the cycle, in turn refreshing the bst capacitor. the boost capacitor is used to generate a high voltage drive supply for the high side switch, which is vcc above v in . power mosfets the sp7662 contains a pair of integrated low resistance n-channel switches designed to drive up to 2a of output current. care should be taken to de-rate the output cur - rent based on the thermal conditions in the system such as ambient temperature, airfow and heat sinking. maximum output current could be limited by thermal limitations of a particular application by taking advantage of the integrated-over-temperature protec - tive scheme employed in the sp7662. the sp7662 incorporates a built-in overtemperature protection to prevent internal overheating. setting output voltages the sp7662 can be set to different output voltages. the relationship in the following formula is based on a voltage divider from the output to the feedback pin v fb , which is set to an internal reference voltage of 0.80v. standard 1% metal flm resistors of surface mount size 0603 are recommended. v out = 0.80v [ r / r2 + ] => r2 = r / [ ( v out / 0.80v ) C ] where r1 = 10k and for v out = 0.80v setting, simply remove r2 from the board. furthermore, one could select the value of the r and r2 combination to meet the exact output voltage setting by restricting the r resistance range such that 10k < r1 < 100k for overall system loop stability. applications information
0 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation applications information and provide low core loss at the high switching frequency. low cost powdered- iron cores have a gradual saturation char - acteristic but can introduce considerable ac core loss, especially when the induc - tor value is relatively low and the ripple current is high. ferrite materials, although more expensive, have an abrupt satura - tion characteristic with the inductance dropping sharply when the peak design current is exceeded. nevertheless, they are preferred at high switching frequen - cies because they present very low core loss while the designer is only required to prevent saturation. in general, ferrite or molypermalloy materials are a better choice for all but the most cost sensitive applications. optimizing effciency the power dissipated in the inductor is equal to the sum of the core and copper losses. to minimize copper losses, the winding resistance needs to be minimized, but this usually comes at the expense of a larger inductor. core losses have a more signifcant contribution at low output current where the copper losses are at a minimum, and can typically be neglected at higher output cur - rents where the copper losses dominate. core loss information is usually available from the magnetics vendor. proper induc - tor selection can affect the resulting power supply effciency by more than 15%! the copper loss in the inductor can be cal - culated using the following equation: p l( c u ) = i 2 l(rms) ? r winding where i l(rms) is the rms inductor current that can be calculated as follows: i l(rms) = i out ( max ) ? + ( . i pp ) 2 3 i out ( max ) inductor selection there are many factors to consider in se - lecting the inductor including core material, inductance vs. frequency, current handling capability, effciency, size and emi. in a typi - cal sp7662 circuit, the inductor is chosen primarily for value, saturation current and dc resistance. increasing the inductor value will decrease output voltage ripple, but degrade transient response. low inductor values pro - vide the smallest size, but cause large ripple currents, poor effciency and require more output capacitance to smooth out the larger ripple current. the inductor must be able to handle the peak current at the switching frequency without saturating, and the copper resistance in the winding should be kept as low as possible to minimize resistive power loss. a good compromise between size, loss and cost is to set the inductor ripple current to be within 20% to 40% of the maximum output current. the switching frequency and the inductor operating point determine the inductor value as follows: l = . v out ? (v in ( max ) - v out ) v in ( max ) ? ? s ? k r ? i out ( max ) where: ? s = switching frequency k r = ratio of the ac inductor ripple current to the maximum output current the peak-to-peak inductor ripple current is: i pp = . v out ? (v in ( max ) - v out ) v in ( max ) ? ? s ?l once the required inductor value is selected, the proper selection of core material is based on peak inductor current and effciency re - quirements. the core must be large enough not to saturate at the peak inductor current i peak = i out ( max ) + i pp 2
nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation applications information output capacitor selection the required esr (equivalent series re - sistance) and capacitance drive the selec - tion of the type and quantity of the output capacitors. the esr must be small enough that both the resistive voltage deviation due to a step change in the load current and the output ripple voltage do not exceed the tolerance limits expected on the output voltage. during an output load transient, the output capacitor must supply all the ad - ditional current demanded by the load until the sp7662 adjusts the inductor current to the new value. in order to maintain v out ,the capacitance must be large enough so that the output voltage is held up while the inductor cur - rent ramps to the value corresponding to the new load current. additionally, the esr in the output capacitor causes a step in the output voltage equal to the current. because of the fast transient response and inherent 00% to 0% duty cycle capability provided by the sp7662 when exposed to output load transients, the output capacitor is typically chosen for esr, not for capaci - tance value. the esr of the output capacitor, combined with the inductor ripple current, is typically the main contributor to output voltage ripple. the maximum allowable esr required to maintain a specifed output voltage ripple can be calculated by : r esr ? v out i pk - pk where: ? v out = p eak-to- p eak o utput v oltage r ipple i pk - pk = p eak-to- p eak i nductor r ipple current the total output ripple is a combination of the esr and the output capacitance value and can be calculated as follows: ?v out = ( i pp ? ( C d) ) 2 + ( i pp ?r esr ) 2 ? s ? c out ? s = switching frequency d = duty cycle c out = o utput c apacitance v alue input capacitor selection the input capacitor should be selected for ripple current rating, capacitance and volt - age rating. the input capacitor must meet the ripple current requirement imposed by the switching current. in continuous conduction mode, the source current of the high-side mosfet is approximately a square wave of duty cycle v out /v in . more accurately, the current wave form is trap - ezoidal, given a fnite turn-on and turn-off, switch transition slope. most of this current is supplied by the input bypass capaci - tors. the rms current handling capability of the input capacitors is determined at maximum output current and under the assumption that the peak-to-peak inductor ripple current is low, it is given by: i cin(rms) = i out ( max ) ? d(1 - d) the worst case occurs when the duty cycle d is 50% and gives an rms current value equal to i out /2. select input capacitors with adequate ripple current rating to ensure reli - able operation. the power dissipated in the input capaci - tor is: p cin = i 2 cin(rms) ? r esr(cin) this can become a signifcant part of power losses in a converter and hurt the overall energy transfer effciency. the input volt - age ripple primarily depends on the input
2 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation sp7662 voltage mode control loop with loop dynamic (srz2cz2+1)(sr1cz3+1) (sr esr c out + 1) [s^2lc out +s(r esr +r dc ) c out +1] v in sr1cz2(srz3cz3+1)(srz2cp1+1) v ramp_pp v out (volts) v ref (volts) notes: r esr = output capacitor equivalent series resistance. r dc = output inductor dc resistance. v ramp_pp = sp7662 internal ramp amplitude peak-to-peak voltage. condition: cz2 >> cp1 & r1 >> rz3 output load resistance >> r esr & r dc r 2 v ref (r 1 + r 2 ) or v out v fbk (volts) type iii voltage loop compensation g am p (s) gain block pwm stage g pw m gain block output stage g out (s) gain block voltage feedback g fbk gain block capacitor esr and capacitance. ignoring the inductor ripple current, the input voltage ripple can be determined by: ?v in = i out ( max ) ? r esr(cin) + i out ( max ) ?v out ?(v in - v out ) v 2 i n ? ? s ? c in the capacitor type suitable for the output capacitors can also be used for the input capacitors. however, exercise extra caution when tantalum capacitors are used. tantalum capacitors are known for catastrophic failure when exposed to surge current, and input capacitors are prone to such surge current when power supplies are connected live to low impedance power sources. although tantalum capacitors have been successfully employed at the input, it is generally not recommended. loop compensation design the open loop gain of the whole system can be divided into the gain of the error ampli - fer, pwm modulator, buck converter output stage, and feedback resistor divider. in order to cross over at the desired frequency cut-off (fco) , the gain of the error amplifer must compensate for the attenuation caused by the rest of the loop at this frequency. the goal of loop compensation is to manipu - late loop frequency response such that its crossover gain at 0db, results in a slope of -20db/decade. the frst step of compensation design is to pick the loop crossover frequency. high crossover frequency is desirable for fast transient response, but often jeopardizes the power supply stability. crossover frequency should be higher than the esr zero but less than /5 of the switching frequency or applications information
3 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation bode plot of type iii error amplifer compensation. frequency (hz) error amplifier gain bandwidth product condition: c22 >> cp1, r1 >> rz3 20 log (rz2/r1) gai n (db) 1/6.28(r22) (cz2) 1/6.28 (r1) (cz3) 1/6.28 (r1) (cz2) 1/6.28 (rz2) (cp1) 1/6.28 (rz3) (cz3) 60khz. the esr zero is contributed by the esr associated with the output capacitors and can be determined by: ? z(esr) = 2 ? c out ? r esr the next step is to calculate the complex conjugate poles contributed by the lc output flter, ? p(lc) = . 2 ? l ? c out when the output capacitors are of a ceramic type, the sp7662 evaluation board requires a type iii compensation circuit to give a phase boost of 80 in order to counteract the effects of an underdamped resonance of the output flter at the double pole frequency. cp1 rz2 cz2 - + v fb comp + - 0.8v cf1 v out r1 68.1k, 1% r set cz3 rz3 r set = 54.48 (k) (v out -0.8) type iii error amplifer compensation circuit applications information
4 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation applications information 5-22vin sd101aws 3.30v, 0-12a np r6 np gnd c7 np c5 100uf vout u1 sp7662 cz2 22nf rs1 1 ? rs2 1 ? c9 6.8nf cp1 100pf d1 rbst c3 22uf c1 22uf r7 np c8 np r1 10k?,1% r8 np cbst 22nf r11 10?,1% cs1 2.2nf cs2 2.2nf c2 22uf cvcc 4.7uf gnd rz3 499?,1% r3 5.11k? dbst r9 60k? rz2 2k?,1% r2 3.2k?,1% 2.7uh, 4.1 m? r12 0 ohms vin c6 100uf css 47nf r4 5.11k? cz3 2200pf c4 0.1uf cf1 100pf isp isn isn lx lx isp 0 ohms pgnd 1 pgnd 2 pgnd 3 pgnd 4 gnd 5 vfb 6 comp 7 ss 8 gnd 9 isn 10 isp 11 swn 12 vinp 13 lx 14 lx 15 lx 16 bst 17 vin 18 gnd 19 gnd 20 uvin 21 vcc 22 lx 23 lx 24 lx 25 lx 26 swn pad 27 gnd pad 28 vin pad 29 evaluation board schematic parts shown for 5v-22v input, 3.3v output
5 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation typical performance characteristics efficiency vs. load at 22v in 50 55 60 65 70 75 80 85 90 95 00 0 2 4 6 8 0 2 output load (a) efficiency (%) vout=5.0v vout=3.3v vout=2.5v vout=.8v vout=.5v vout=.2v vout=0.8v efficiency vs. load at 12v in 50 55 60 65 70 75 80 85 90 95 00 0 2 4 6 8 0 2 output load (a) efficiency (%) vout=5.0v vout=3.3v vout=2.5v vout=.8v vout=.5v vout=.2v vout=0.8v efficiency vs. load at 5.0v in 70 75 80 85 90 95 00 0 2 4 6 8 0 2 output load (a) efficiency (%) vout=3.3v vout=2.5v vout=.8v vout=.5v vout=.2v vout=0.8v efficiency vs. load at 3.3v in 70 75 80 85 90 95 00 0 2 4 6 8 0 2 output load (a) efficiency (%) vout=2.5v vout=.8v vout=.5v vout=.2v vout=0.8v
6 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation vout ripple output ripple, no load vout ripple output ripple, iout=12a vin vout start up response, no load soft start iout 5a/div vin vout start up response, iout=6a soft start iout 5a/div vin vout start up response, iout=12a soft start iout 10a/di vout transient load step response, iout=6a -12a iout 5a/div typical performance characteristics
7 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation typical performance characteristics vout transient load step response, iout=0a -2a iout 5a/div vout vs load at 12vin 3.32 3.34 3.36 3.38 0 2 4 6 8 0 2 output load (a) vout (v) vout = 3.3 v vout output short circuit iout 0a/div soft start vout vin softstart iout 5a/div ocp hiccup response
8 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation p ackage: 26 pin dfn
9 nov 3-06 rev ae sp7662 wide input voltage range 2a, 300khz buck regulator ? 2006 sipex corporation ordering information part number junction temperature package sp7662er/tr..................................-40c to +25c............ .................................26 pin 7 x 4 dfn (option 2) sp7662er-l/tr.............................-40c to +25c.......................... (lead free) 26 pin 7 x 4 dfn (option 2) /tr = tape and reel pack quantity is 3,000 26 pin dfn. sipex corporation headquarters and sales offce 233 south hillview drive milpitas, ca 95035 tel: (408) 934-7500 fax: (408) 935-7600 sipex corporation reserves the right to make changes to any products described herein. sipex does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others.

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