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EN6337QI 3a voltage mode synchronous buck pwm dc-dc converter with integrated inductor www.enpirion.com description the EN6337QI is a powe r system on a chip (powersoc) dc-dc converter. it integrates mosfet switches, small-signal circuits, compensation, and the i nductor in an advanced 4mm x 7mm qfn package. the EN6337QI is specific ally designed to meet the precise voltage and fast transient requirements of present and future high- performance, low-power processor, dsp, fpga, memory boards and system level applications in distributed power architecture. the device?s advanced circuit techniques, ultra high switching frequency, and proprietary integrated inductor technology deliver high-qual ity, ultra compact, non-isolated dc-dc conversion. the enpirion solution significantly helps in system design and productivity by offering greatly simplified board design, layout and manufacturing requirements. in addition, a reduction in the number of vendors required for the complete power solu tion helps to enable an overall system cost savings. all enpirion products ar e rohs compliant and lead-free manufacturing environment compatible. figure 1: total solution footprint pwm mode (not to scale) total area 75 mm 2 features ? integrated inductor, mosfets, controller ? minimal external components. ? up to 3a continuous output current capability. ? 2 mhz operating frequency. switching frequency can be phase locked to an external clock. ? high efficiency, up to 95%. ? wide input voltage range of 2.5v to 6.6v. ? light load mode with programmable set point. ? output enable pin and power ok signal. ? programmable soft-start time. ? under voltage lockout, over current, short circuit and thermal protection. ? rohs compliant, msl level 3, 260c reflow. application ? point of load regulation for processors, dsps, fpgas, and asics ? noise sensitive applications such as a/v, rf and gbit i/o ? low voltage, distributed power architectures such as 0.8v, 1.0v, 1.2, 2.5v, 3.3v, 5v rails ? blade servers, raid storage systems, lan/san adapter cards, wireless base stations, industrial automation, test and measurement, embedded computing, communications, and multi-function printers. ? ripple sensitive applications ? beat frequency sensitive applications 05800 6/17/2011 rev: b
EN6337QI ? enpirion 2011 all rights reserved, e&oe 2 www.enpirion.com figure 2: typical application schematic (pwm mode) ordering information part number temp rating (c) package EN6337QI -40 to +85 38-pin qfn t&r EN6337QI3 -40 to +85 38-pin qfn t&r EN6337QI-e qfn evaluation board pin assignments (top view) figure 3: top view pinout diagram (not to scale) note: all perimeter pins must be soldered to pcb. pin description pin name function 1-2, 12, 34-38 nc(sw) no connect ? these pins are internally connected to the common switching node of the internal mosfets. they are not to be electrica lly connected to any external signal, ground, or voltage. failure to follow this guideline may result in damage to the device. 3-4, 22-25 nc no connect ? these pins may be internally connected. do not connect to each other or to any other electrical signal. failure to follo w this guideline may result in device damage. 5-11 vout regulated converter output. connect these pins to the load and place output capacitor between these pins and pgnd pins 13-15. 13-18 pgnd input/output power ground. connect these pi ns to the ground electrode of the input and output filter capacitors. see vout and pvin pin descriptions for more details. 19-21 pvin input power supply. connect to input power supply. decouple with input capacitor to pgnd pins 16-18. 26 llm/sync dual function pin providing llm enable and external clock synchronization (see application section). at static logic high, device will allow automatic engagement of light load mode. at static logic low, the device is forced into pwm only. a clocked input to this pin will synchronize the internal switching frequenc y to the external signal. if this pin is left floating, it will pull to a static logic high, enabling llm. 27 enable input enable. applying logic high enables t he output and initiates a soft-start. applying logic low disables the output. 28 pok power ok is an open drain transistor used for po wer system state indication. pok is logic high when vout is within -10% of vout nominal. 29 rllm programmable llm engage resistor to agnd allo ws for adjustment of load current at which light-load mode engages. can be left open for pwm only operation. 30 ss soft-start node. the soft-start capacitor is connected between this pin and agnd. the value of this capacitor determines the startup time. 31 vfb external feedback input. the feedback loop is closed through this pin. a voltage divider at vout is used to set the output voltage. the midpoint of the divider is connected to vfb. a phase lead capacitor from this pin to vout is also required to stabilize the loop. 32 agnd analog ground. this is the controller ground return. connect to a quiet ground. 33 avin input power supply for the controller. connect to input voltage at a quiet point. 39 pgnd device thermal pad to be connected to the system gnd plane. see layout recommendations section. 05800 6/17/2011 rev: b
EN6337QI ? enpirion 2011 all rights reserved, e&oe 3 www.enpirion.com absolute maximum ratings caution: absolute maximum ratings are stress ratings only. functional operation beyond the recommended operating conditions is not implied. stre ss beyond the absolute maximum ratings may impair device life. exposure to absolute maximum ra ted conditions for extend ed periods may affect device reliability. parameter symbol min max units supply voltage ? pvin, avin, vout v in -0.5 7.0 v pin voltages ? enable, pok, llm/sync -0.5 v in +0.3 v pin voltages ? vfb, ss, rllm -0.5 2.75 v storage temperature range t stg -65 150 c maximum operating junction temperature t j-abs max 150 c reflow temp, 10 sec, msl3 jedec j-std-020a 260 c esd rating - all pins (based on hbm) 2000 v recommended operating conditions parameter symbol min max units input supply voltage v in 2.5 6.6 v operating junction temperature t j-op - 40 125 c operating ambient temperature t amb - 40 85 c reflow temp, 10 sec, msl3 jedec j-std-020a 260 c thermal characteristics parameter symbol min typ max units thermal shutdown t sd 160 c thermal shutdown hysteresis t sdh 35 c thermal resistance: junction to ambient ( note 1 ) ja 30 c/w thermal resistance: junction to case jc 3 c/w note 1 : based on 2oz. external copper layers and proper thermal design in line with eia/jedec jesd51-7 standard for high thermal conductivity boards. 05800 6/17/2011 rev: b
EN6337QI ? enpirion 2011 all rights reserved, e&oe 4 www.enpirion.com electrical characteristics note: v in =6.6v over operating temperature range unless otherwi se noted. typical values are at ta = 25c. parameter symbol test conditions min typ max units operating input voltage v in 2.5 6.6 v under voltage lock-out ? v in rising v uvlor voltage above which uvlo is not asserted 2.3 v under voltage lock-out ? v in falling v uvlof voltage below which uvlo is asserted 2.075 v shut-down supply current i s enable=0v 100 a operating quiescent current i q llm/sync = high 650 a feedback pin voltage EN6337QI EN6337QI3 v fb feedback node voltage at: v in = 5v, iload = 0, t a = 25c 0.7425 0.735 0.75 0.75 0.7575 0.765 v feedback pin voltage EN6337QI EN6337QI3 v fb feedback node voltage at: 2.5v v in 6.6v 0a iload 3a, t a = -40 to 85c 0.735 0.7275 0.75 0.75 0.765 0.7725 v feedback pin input leakage current (note 1) i fb vfb pin input leakage current -5 5 na v out rise time (note 1) t rise measured from when v in > v uvlor & enable pin voltage crosses its logic high threshold to when v out reaches its final value. c ss = 15 nf 0.9 1.2 1.5 ms soft start capacitor range c ss_range 10 68 nf output drop out voltage resistance (note 1) v do r do v inmin - v out at full load input to output resistance 210 70 315 105 mv m continuous output current i out pwm mode llm mode (note 2) 0 0.002 3 3 a over current trip level i ocp v in = 5v, v out = 1.2v 5 a disable threshold v disable enable pin logic low. 0.0 0.6 v enable threshold v enable enable pin logic high 2.5v v in 6.6v 1.8 v in v enable lockout time t enlockout 4.2 ms enable pin input current (note 1) i enable enable pin has ~180k pull down 40 a switching frequency (free running) f sw free running frequency of oscillator 1.9 mhz external sync clock frequency lock range f pll_lock range of sync clock frequency 1.5 2.3 mhz sync input threshold ? low (llm/sync pin) v sync_lo sync clock logic level 0.8 v sync input threshold ? high (llm/sync pin) (note 3) v sync_hi sync clock logic level 1.8 2.5 v pok lower threshold pok lt output voltage as a fraction of expected output voltage 90 % pok output low voltage v pokl with 4ma current sink into pok 0.4 v 05800 6/17/2011 rev: b
EN6337QI ? enpirion 2011 all rights reserved, e&oe 5 www.enpirion.com parameter symbol test conditions min typ max units pok output hi voltage v pokh 2.5v v in 6.6v v in v pok pin v oh leakage current (note 1) i pokl pok high 1 a llm engage headroom minimum v in -v out to ensure proper llm operation 800 mv llm logic low (llm/sync pin) v llm_lo llm static logic level 0.3 v llm logic high (llm/sync pin) v llm_hi llm static logic level 1.5 v llm/sync pin current llm/sync pin is <2.5v <100 na note 1 : parameter guaranteed by design. note 2 : llm operation is normally only guaranteed above the minimum specified output current. contact enpirion applications support for designs that need to operate at a lower i out . note 3 : for proper operation of the synchronization circuit, the high-level amplitude of the sync signal should not be above 2.5v. 05800 6/17/2011 rev: b
EN6337QI ? enpirion 2011 all rights reserved, e&oe 6 www.enpirion.com typical performance characteristics efficiency v in = 3.3v, v out (from top to bottom) = 2.5, 1.8, 1.2, 1.0v efficiency v in = 5.0v, v out (from top to bottom) = 3.3, 2.5, 1.8, 1.2, 1.0v pwm output ripple: v in = 3.3v, v out = 1.0v, i out = 3a c in = 22 f, c out = 47 f/1206 + 10uf/0805 pwm output ripple: v in = 3.3v, v out = 1.0v, i out = 3a c in = 22 f, c out = 47 f/1206 + 10uf/0805 pwm output ripple: v in = 5.0v, v out = 1.0v, i out = 3a c in = 22 f, c out = 47 f/1206 + 10uf/0805 pwm output ripple: v in = 5.0v, v out = 1.0v, i out = 3a c in = 22 f, c out = 47 f/1206 + 10uf/0805 pwm/llm efficiency vs. load performance at vin=3.3v 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 0.01 0.1 1 10 load (a) efficiency ( %) vout=2.5 vout=1.8 vout=1.2 vout=1 vout=1 vout=1.2 vout=1.8 vout=2.5 #ref! pwm/llm efficiency vs. load performance at vin=5v 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 0.01 0.1 1 10 load (a) effi ci ency (% ) vout=3.3 vout=2.5 vout=1.8 vout=1.2 vout=1 vout=1 vout=1.2 vout=1.8 vout=2.5 vout=3.3 20 mhz bw limit 20 mhz bw limit 500 mhz bw 500 mhz bw 05800 6/17/2011 rev: b
EN6337QI ? enpirion 2011 all rights reserved, e&oe 7 www.enpirion.com llm output ripple: v in = 3.3v, v out = 1.0v, i out = 0.1a, c in = 22 f, c out = 2x47 f/1206 llm output ripple: v in = 5.0v, v out = 1.0v, i out = 0.1a, c in = 22 f, c out = 2x47 f/1206 load transient: v in = 5.0v, v out = 1.0v, llm enabled ch.1: v out , ch.2: i out = 0.01 ? 3a c in = 22 f, c out = 2x47 f/1206 load transient: v in = 5.0v, v out = 3.0v, llm enabled ch.1: v out , ch.2: i out = 0.01 ? 3a c in = 22 f, c out = 2x47 f/1206 05800 6/17/2011 rev: b
EN6337QI ? enpirion 2011 all rights reserved, e&oe 8 www.enpirion.com pwm load transient: v in = 5.0v, v out = 1.0v ch.1: v out , ch.2: i out = 0 ?3a c in = 22 f, c out = 47 f/1206 + 10f/0805 pwm load transient: v in = 5.0v, v out = 3.0v ch.1: v out , ch.2: i out = 0 ?3a c in = 22 f, c out = 47 f/1206 + 10f/0805 power up/down at no load: v in /v out = 5.5v/3.3v, 15nf soft-start capacitor, c out 50f ch.1: enable, ch. 2: v out , ch. 3: pok, ch.4: i out power up/down into 1.1 load: v in /v out = 5.5v/3.3v, 15nf soft-start capacitor, c out 50f ch.1: enable, ch. 2: v out , ch. 3: pok, ch.4: i out 05800 6/17/2011 rev: b
EN6337QI ? enpirion 2011 all rights reserved, e&oe 9 www.enpirion.com functional block diagram figure 4: functional block diagram functional description synchronous buck converter the EN6337QI is a synchronous, programmable power supply with integrated power mosfet switches and integrated inductor. the nominal input voltage range is 2.5v to 6.6v. the output voltage is programmed using an exte rnal resistor divider network. the control l oop is voltage-mode with a type iii compensation net work. much of the compensation circuitry is internal to the device. however, a phase lead capacitor is required along with the output volt age feedback resistor divider to complete the type iii compensation network. the device uses a low-noise pwm topology and also integr ates a unique light-load mode (llm) to improve efficiency at light output load currents. llm can be disabled with a logic pin. up to 3a of continuous output current can be drawn from this converter. the 2 mhz switching frequency allows the use of small size input / output capacitors, and enables wide loop bandw idth within a small foot print. protection features: the power supply has t he following protection features: ? over-current protecti on (to protect the ic from excessive load current) ? thermal shutdown with hysteresis. ? under-voltage lockout circuit to keep the converter output off while the input voltage is less than 2.3v. 05800 6/17/2011 rev: b
EN6337QI ? enpirion 2011 all rights reserved, e&oe 10 www.enpirion.com additional features: ? the switching frequency can be phase- locked to an external clock to eliminate or move beat frequency tones out of band. ? soft-start circuit allowing controlled startup when the converter is initially powered up. the soft start time is programmable with an appropriate choice of soft start capacitor. ? power good circuit indicating the output voltage is greater t han 90% of programmed value as long as feedback loop is closed. ? to maintain high efficiency at low output current, the device inco rporates automatic light load mode operation. enable operation the enable pin provides a means to enable normal operation or to shut down the device. when the enable pin is asserted (high) the device will undergo a norma l soft start. a logic low on this pin will power the device down in a controlled manner. from the moment enable goes low, there is a fixed lock out time before the output will respond to the enable pin re- asserted (high) . this lock out is activated for even very short logic low pulses on the enable pin. see the elec trical characteristics table for technical specifications for this pin. llm/sync pin this is a dual func tion pin providing llm enable and external clock synchronization. at static logic high, devic e will allow automatic engagement of light load mode. at static logic low, the device is fo rced into pwm only. a clocked input to this pin will synchronize the internal switching frequency ? llm mode is not available if this input is clocked. if this pin is left floating, it will pull to a static logic high, enabling llm. frequency synchronization the switching frequency of the dc/dc converter can be phase-locked to an external clock source to move unwanted beat frequencies out of band. to avail this feature, the clock source should be connected to the llm/sync pin. an activity detector recognizes the presence of an exte rnal clock signal and automatically phase-locks t he internal oscillator to this external clock. phase-lock will occur as long as the clock frequency is in the range specified in the electrical characteristics table. for proper operation of the synchronization circuit, the high-level amplitude of the sync signal should not be above 2.5v. please note llm is not available when synchronizing to an external frequency. spread spectrum mode the external clock frequency may be swept between the limits specifie d in the electrical characteristics table at repetition rates of up to 10 khz in order to reduce emi frequency components. soft-start operation during soft-start, the output voltage is ramped up gradually upon start-up. the output rise time is controlled by the choice of soft-start capacitor, which is pl aced between the ss pin (30) and the agnd pin (32). rise time: t r (c ss * 80k ) 25% during start-up of the converter, the reference voltage to the error amplifier is linearly increased to its final level by an internal current source of approximately 10ua. typical soft- start rise time is ~1.2ms with ss capacitor value of 15nf. the rise time is measured from when v in > v uvlor and enable pin voltage crosses its logic high threshold to when v out reaches its programmed value. please note llm function is disabled during the soft-start ramp-up time. pok operation the pok signal is an open drain signal (requires a pull up resistor to v in or similar voltage) from the converter indicating the output voltage is within the specified range. the pok signal wi ll be logic high (v in ) when the output voltage is above 90% of programmed v out . if the output voltage goes below this threshold, the pok signal will be logic low. 05800 6/17/2011 rev: b
EN6337QI ? enpirion 2011 all rights reserved, e&oe 11 www.enpirion.com light load mode (llm) operation the EN6337QI uses a proprietary light load mode to provide high efficiency at low output currents. when the llm/ sync pin is high, the device is in automatic llm ?detection? mode. when the llm/sync pin is low, the device is forced into pwm mode. in automatic llm ?detection? mode, when a light load condition is detected, the device will: (1) step v out up by approximately 1.0% above the nominal operati ng output voltage setting, v nom and as low as -0.5% below v nom , and then (2) shut down unnecessary circuitry, and then (3) monitor v out . when v out falls below v nom , the device will repeat (1), (2), and (3). the voltage step up, or pre-positioning, improv es transient droop when a load transient causes a transition from llm mode to pwm mode. if a load transient occurs, causing v out to fall below the threshold v min , the device will ex it llm operation and begin normal pwm operation. figure 5 demonstrates v out behavior during transition into and out of llm operation. v out i out llm ripple pwm ripple v max v nom v min load step figure 5: v out behavior in llm operation. many multi-mode dcdc converters suffer from a condition that occurs when the load current increases only slowly so that there is no load transient driving v out below the v min threshold. in this condition, the device would never exit llm operation. this could adversely affect efficiency and cause unwanted ripple. to prevent this from occurring, the EN6337QI periodically exits llm mode into pwm mode and measures the load cu rrent. if the load current is above the llm threshold current, the device will remain in pwm mode. if the load current is below the llm threshold, the device will re-enter llm operati on. there may be a small overshoot or undershoot in v out when the device exits and re-enters llm. the load current at which the device will enter llm mode is a function of input and output voltage, and the rllm pin resistor. contact enpirion applications support for details regarding the optimization of this resistor for specific operating co nditions. for pwm only operation, the rllm pin can be left open. to ensure normal llm operation, llm mode should be enabled and disabled with specific sequencing. for applications with explicit llm pin control, enable llm after v in ramp up is complete. for applications with only enable control, tie llm to enable; enable the device after v in ramp up is complete, and disable the device before vin ramp down begins. for designs with enable and llm tied to v in , make sure the device soft-start time is longer than the v in ramp-up time. llm will start operating after the soft-star t time is completed. note: for proper llm operation the EN6337QI requires a minimum difference between v in and v out , and a minimum llm load requirement as specif ied in the electrical characteristics table. for llm designs requiring lower voltage headroom or a lower minimum load, contact enpirion applications support. over-current protection the current limit function is achieved by sensing the current fl owing through the power pfet. when the sensed current exceeds the over current trip point, both power fets are turned off for the remainder of the switching cycle. if the over-current condition is removed, the over-current protection circuit will enable normal pwm operation. if the over-current condition persists, the soft start capacitor will gradually discharge causing the output voltage to fall. when the ocp fault is removed, the output voltage will ramp back up to the desired voltage. this circuit is designed to provide high noise immunity. 05800 6/17/2011 rev: b
EN6337QI ? enpirion 2011 all rights reserved, e&oe 12 www.enpirion.com thermal overload protection thermal shutdown circuit will disable device operation when the j unction temperature exceeds approximately 150oc. after a thermal shutdown event, when the junction temperature drops by approx 20oc, the converter will re-start with a normal soft-start. input under-voltage lock-out internal circuits ensure that the converter will not start switching unt il the input voltage is above the specified minimum voltage. hysteresis and input de-glitch circuits ensure high noise immunity and prevent false uvlo triggers. compensation the EN6337QI uses a type 3 compensation network. as noted earlier, a piece of the compensation network is the phase lead capacitor ca in figure 6. this network is optimized for use with about 50-100 f of output capacitance and wil l provide wide loop bandwidth and excellent transient performance for most applications. voltage mode operation provides high noise immunity at light load. in some applications, modifications to the compensation may be required. for more information, contact enpirion applications engineering support. application information the EN6337QI output voltage is programmed using a simple resistor divider network. figure 6 shows the resistor di vider configuration. ) 75 .0 ( * 75 .0 200 v vout ra rb k ra ? = = figure 6: v out resistor divider & compensation capacitor an additional compensation capacitor c a is also required in parallel with the upper resistor. input capacitor selection the EN6337QI requires about 20uf of input capacitance. low-cost, low-esr ceramic capacitors should be used as input capacitors for this converter. the dielectric must be x5r or x7r rated. y5v or equivalent dielectric formulations must not be used as these lose too much capacitance with frequency, temperature and bias voltage. in some applications, lower value capacitors are needed in parallel with the larger, capacitors in order to provide high frequency decoupling. recommended input capacitors description mfg p/n 10 f, 10v, 10% x7r, 1206 (2 capacitors needed) murata grm31cr71a106ka01l taiyo yuden lmk316b7106kl-t 22 f, 10v, 20% x5r, 1206 (1 capacitor needed) murata grm31cr61a226me19l taiyo yuden lmk316bj226ml-t output capacitor selection the EN6337QI has been nom inally optimized for use with approximately 50-100 f of output capacitance. low esr ceramic capacitors are required with x5r or x7r rated dielectric formulation. y5v or equivalent dielectric formulations must not be used as these lose too much capacitance with frequency, temperature and bias voltage. output ripple voltage is determined by the aggregate output capacitor impedance. output impedance, denoted as z, is comprised of effective series resistance, esr, and effective series inductance, esl: z = esr + esl placing output capacitor s in parallel reduces the impedance and will henc e result in lower pwm ripple voltage. in addition, higher output capacitance will improve overall regulation and ripple in light-load mode. n total zzzz 1 ... 111 21 +++= 05800 6/17/2011 rev: b
EN6337QI ? enpirion 2011 all rights reserved, e&oe 13 www.enpirion.com typical pwm ripple voltages output capacitor configuration typical output ripple (mvp-p) (as measured on EN6337QI evaluation board)* 1 x 47 f 25 47 f + 10 f 14 * note: 20 mhz bw limit recommended output capacitors description mfg p/n 47uf, 6.3v, 20% x5r, 1206 (1 or 2 capacitors needed) murata grm31cr60j476me19l taiyo yuden jmk316bj476ml-t 10uf, 10v, 10% x5r, 1206 (optional 1 capacitor in parallel with 47uf above) murata grm31cr71a106ka01l taiyo yuden lmk316bj226ml-t for best llm performanc e, we recommend using just 2x47uf capac itors mentioned in the above table, and no 10uf capacitor. the v out sense point should be just after the last output filter capacit or right next to the device. additional bulk output capacitance beyond the above recommendations can be used on the output node of the EN6337QI as long as the bulk capacitors are far enough from the v out sense point such that they don?t interfere with the control loop operation. in some cases modifications to the compensation or output filter capacitance may be required to optimize device performance such as transient response, ripple, or hold-up time. the EN6337QI prov ides the capability to modify the control loop response to allow for customization for such applications. for more information, contact enpirion applications engineering support. power-up sequencing during power-up, enable should not be asserted before pvin, and pvin should not be asserted before avin. tying all three pins together meets these requirements. thermal considerations the enpirion EN6337QI dc-dc converter is packaged in a 7x4x1.85mm 38-pin qfn package. the qfn package is constructed with copper lead frames that have exposed thermal pads. the recommended maximum junction temperature for continuous operation is 125c. continuous operation above 125c will reduce long-term reliability. the device has a thermal overload prot ection circuit designed to shut it off at a junction temperature specified in the electrical characteristics table. the silicon is mounted on a copper thermal pad that is exposed at the bottom of the package. the thermal resistance from the silicon to the exposed thermal pad is very low. in order to take advantage of this low resistance, the exposed thermal pad on the package should be soldered directly on to a copper ground pad on the printed circuit board (pcb). the pcb then acts as a heat sink. in order for the pcb to be an effective heat sink, the device thermal pad should be coupled to copper ground planes or special heat sink structures designed into the pcb (refer to the layout recommendations section). the junction temperature, t j , is calculated from the ambient temperature, t a , the device power dissipation, pd, and the device junction-to- ambient thermal resistance, ja in c/w, as follows: t j = t a + (p d ) ( ja ) the junction temperature, t j , can also be expressed in terms of the device case temperature, t c , and the device junction-to- case thermal resistance, jc in c/w, as follows: t j = t c + (p d ) ( jc ) the device case temperature, t c , is the temperature at the c enter of the exposed thermal pad at the bottom of the package. the device junction-to-ambient and junction-to- case thermal resistances, ja and jc , are shown in the thermal ch aracteristics table on page 3. the jc is a function of the device and the qfn package design. the ja is a function of jc and the user?s system design parameters that include the thermal effectiveness of the cust omer pcb and airflow. 05800 6/17/2011 rev: b
EN6337QI ? enpirion 2011 all rights reserved, e&oe 14 www.enpirion.com the ja value shown in the thermal characteristics table on page 3 is for free convection with the devi ce heat sunk (through the thermal pad) to a copper plated four-layer pc board with a full ground and a full power plane following eia/ jedec jesd51-7 standard. the ja can be reduced with the use of forced air convection. because of the strong dependence on the thermal effectiveness of the pcb and the system design, the actual ja value will be a functi on of the specific application. layout recommendations figure 7 shows critical components and layer 1 traces of a recommended minimum footprint EN6337QI layout with enable tied to v in in pwm mode. alternate en able configurations, and other small signal pins need to be connected and routed according to specific customer application. pl ease see the gerber files on the enpirion website www.enpirion.com for exact dimensions and other layers. please refer to this figure while reading the layout recommendations in this section. recommendation 1: input and output filter capacitors should be placed on the same side of the pcb, and as close to the EN6337QI package as possible. they should be connected to the device with very short and wide traces. do not use thermal reliefs or spokes when connecting the capacitor pads to the respective nodes. the +v and gnd traces between the capacitors and the EN6337QI should be as close to each other as possible so that the gap between the two nodes is minimized, even under the capacitors. recommendation 2: three pgnd pins are dedicated to the input circuit, and three to the output circuit. the slit in figure 7 separating the input and output gnd circuits helps minimize noise coupling between the converter input and output switching loops. recommendation 3: the system ground plane should be the first layer immediately below the surface layer. this ground plane should be continuous and un-interrupted below the converter and the input/output capacitors. please see the gerber files on the enpirion website www.enpirion.com . recommendation 4: the large thermal pad underneath the component must be connected to the system ground plane through as many vias as possible. figure 7: top pcb layer critical components and copper for minimum footprint the drill diameter of the vias should be 0.33mm, and the vias must have at least 1 oz. copper plating on the inside wall, making the finished hole size around 0.20-0.26mm. do not use thermal reliefs or spokes to connect the vias to the ground plane. this connection provides the path for heat dissipation from the converter. please see figures: 7, 8, and 9. recommendation 5 : multiple small vias (the same size as the thermal vias discussed in recommendation 4 should be used to connect ground terminal of the input capacitor and output capacitors to the system ground plane. it is preferred to put these vias under the capacitors along the edge of the gnd copper closest to the +v copper. please see figure 7. these vias connect the input/output filter capacitors to the gnd plane, and help reduce parasitic inductances in the input and output current loops. if the vias cannot be placed under c in and c out , then put them just outside the capacitors along the gnd slit separating the two components. do not use thermal reliefs or spokes to connect these vias to the ground plane. 05800 6/17/2011 rev: b
EN6337QI ? enpirion 2011 all rights reserved, e&oe 15 www.enpirion.com recommendation 6 : avin is the power supply for the internal small-signal control circuits. it should be connected to t he input voltage at a quiet point. in figure 7 this connection is made at the input capacitor close to the v in connection. recommendation 7: the layer 1 metal under the device must not be more than shown in figure 7. see the section regarding exposed metal on bottom of package. as with any switch-mode dc/dc converte r, try not to run sensitive signal or cont rol lines underneath the converter package on other layers. recommendation 8: the v out sense point should be just after the last output filter capacitor. keep the sense trace as short as possible in order to avoid noise coupling into the control loop. recommendation 9: keep r a , c a , and r b close to the vfb pin (see figures 6 and 7). the vfb pin is a high-impedance, sensitive node. keep the trace to this pin as short as possible. whenever possible, connect r b directly to the agnd pin instead of going through the gnd plane. design considerations for lead-frame based modules exposed metal on bottom of package lead frames offers many advantages in thermal performance, in reduced electrical lead resistance, and in overall foot print. however, they do require some special considerations. in the assembly process lead frame construction requires that, for mechanical support, some of the lead-frame cantilevers be exposed at the point where wire-bond or internal passives are attached. this results in several small pads being exposed on the bottom of the package. only the large thermal pad and the perimeter pads are to be soldered to the pc board. the pcb top layer under the EN6337QI should be clear of any metal except for the large thermal pad. the ?grayed-out? region in figure 8 represents the area that should be clear of any metal (traces, vias, or planes), on the top layer of the pcb. figure 8: lead-frame exposed metal. grey area highlights exposed metal below which there should not be any metal (traces, vias, or planes) on the top layer of pcb. v in copper covered by soldermask acceptable near or under this exposed pad. 05800 6/17/2011 rev: b
EN6337QI ? enpirion 2011 all rights reserved, e&oe 16 www.enpirion.com recommended pcb footprint figure 9: EN6337QI package pcb footprint dimensions in mm 05800 6/17/2011 rev: b
EN6337QI ? enpirion 2011 all rights reserved, e&oe 17 www.enpirion.com package and mechanical figure 10: EN6337QI package dimensions contact information enpirion, inc. perryville iii corporate park 53 frontage road - suite 210 hampton, nj 08827 usa phone: 1.908.894.6000 fax: 1.908.894.6090 enpirion reserves the right to make changes in circuit design and/or specif ications at any time without notice. information fur nished by enpirion is believed to be accurate and reliable. enpirion assumes no respons ibility for its use or for infringement of patents or other th ird party rights, which may result from its use. enpirion products are not authorized for us e in nuclear control systems, as critical components in life su pport systems or equipment used in hazardous environment without the ex press written authority from enpirion. 05800 6/17/2011 rev: b

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