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| MP2905 3v-28v input, hysteretic synchronous step-down controller MP2905 rev. 0.91 www.monolithicpower.com 1 4/18/2011 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2011. all rights reserved. the future of analog ic technology description the MP2905 is a hysteretic voltage-mode control, synchronous pwm buck controller. the output voltage can be regulated from 0.6v to 0.9*vin. it achieves high output current over a wide input supply range from 3v-28v. MP2905 integrates an internal ldo regulator that makes the controller function at a wide input supply. hysteretic voltage-mode control provides fast transient response without additional loop compensation. an adjustable soft-start prevents inrush current at turn-on. the device senses high-side switch voltage drop for hiccup current limit and short current protection. the frequency is adjustable from 200khz to 500khz. the MP2905 is available in 10-pin msop package, provides a very compact system solution with minimal reliance on external components. features ? wide 3v to 28v operating input range ? output adjustable from 0.6v to 0.9*vin ? switching frequency from 200khz to 500khz ? programmable soft-start ? hiccup current limit ? lossless peak current sensing ? msop-10 package applications ? motherboard power supplies ? agp and pci-express power supplies ? graphic-card power supplies ? set-top boxes ? point-of-load power supplies typical application
MP2905- 3v to 28v input, hysteret ic synchronous step- down controller MP2905 rev. 0.91 www.monolithicpower.com 2 4/18/2011 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2011. all rights reserved. ordering information *for tape & reel, add suffix ?z (eg. MP2905ek?z). for rohs compliant packaging, add suffix ?lf (eg. MP2905ek?lf?z) package reference fb ss ref gnd lg 1 2 3 4 5 10 9 8 7 6 ilim in hg sw bst top view absolute maxi mum ratings (1) in to gnd ??... ?.. ?............-0.3v to +30v ref to gnd ????................-0.3v to +6.5v in to ref ??........ ?................-0.3v to +25v ss to gnd ????..?.. -0.3v to (ref + 0.3v) lg to gnd ?????.. -0.3v to (ref + 0.3v) bst to gnd????????.. -0.3v to 36.5v bst to sw?????..??.?.-0.3v to + 6.5v sw to gnd???..????.?.-0.3v to +30v hg to sw ????..?.-0.3v to (bst + 0.3) v fb to gnd????????..?-0.3v to +6.5v ilim to gnd ......... ?..........-0.3v to (in + 0.3v) ilim to sw ???????.-0.6v to (in + 0.3v) hg and lg continuous current...250ma rms continuous power dissipation (ta = +25c) (2) ??????????????????.0.77w junction temperature.............................+140c storage temperature range . ???.....................................-65c to +150c lead temperature (soldering, 10s) ??........................................................+300c recommended operating conditions (3) supply voltage v in .............................. 3v to 28v operating temperature ............. ?20 c to +85 c thermal resistance (4) ja jc msop10-ep ............................. 150 65 c/w notes: 1) exceeding these ratings may damage the device. 2) the maximum allowable power dissipation is a function of the maximum junction temperature. t j (max) the junction-to- ambient thermal resistance. ja and the ambient temperature, t a the maximum allowable power dissipation at any ambient temperature is calculated using: p d (max)=(t j (max)-t a )/ ja . exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. internal thermal shutdown circuitry protects the device from permanent damage. thermal shutdown engages at t j =140 o c(typ) and disengages at t j =120 o c(typ) 3) the device is not guaranteed to function outside of its operating conditions. 4) measured on jesd51-7 4-layer board. part number* package top marking temperature MP2905ek msop10 2905e ?20 c to +85 c MP2905- 3v to 28v input, hysteret ic synchronous step- down controller MP2905 rev. 0.91 www.monolithicpower.com 3 4/18/2011 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2011. all rights reserved. electrical characteristics v in =12v, 4.7uf capacitor from ref, 0.01uf capacitor from ss to gnd; v fb =0.65v; v sw =v gnd =0v; v ilim =11.5v; hg=unconnected; lg=unconnected; t a =25 o c, unless otherwise noted. parameter condition min typ max unit in supply voltage 3 (5) 28 v ref output voltage i ref =10ma 4.75 5.0 5.25 v ref maximum output current 20 ma bst output voltage i bst =10ma 5.0 v bst maximum output current 20 ma ref undervoltage lockout (uvlo) rising 2.6 2.8 3 v falling 2.25 2.45 2.65 v hysteresis 350 mv supply current no switching, v fb =0.65v v in =12v 0.6 2 ma v in =v ref =5v 0.7 2 v in =v ref =3.3v 0.6 2 output regulation accuracy v fb peak 0.593 0.6 0.607 v output regulation hysteresis 22 mv fb propagation delay fb falling to lg falling 50 ns fb rising to hg falling 70 ns overvoltage- protection(ovp) threshold 0.7 0.75 0.8 v high-side current ? sense program current t a =85 o c 60 ua t a =25 o c 42.5 50 57.5 ua soft-start internal resistance 60 80 100 k fault hiccup internal ss pulldown current v sw MP2905- 3v to 28v input, hysteret ic synchronous step- down controller MP2905 rev. 0.91 www.monolithicpower.com 5 4/18/2011 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2011. all rights reserved. typical performanc e characteristics v in =12v, v out =1.8v, i out =12a, l1=1.5h(dcr=3.41m ? ), c out =100f *2+330f, t a =+25c, high side mos:si7112dn-t1-e3, low side mos: si7336adp-t1-e3 unless otherwise noted. line regulation supply current (no switching) vs. input voltage v fb =0.65v efficiency frequency vs. input voltage no load, feedforward cap=22nf 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 5 10 15 20 25 30 v in (v) i in (ma) 0 10 20 30 40 50 60 70 80 90 100 024681012 i out (a) efficiency(%) v in =5.5v v in =12v v in =28v -2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50 2.00 024681012 load regulation(%) i out (a) load regulation v in =5.5v v in =12v v in =28v -2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50 2.00 51015202530 line regulation(%) v in (v) i out =6a i out =0a i out =12a 0 50 100 150 200 250 300 51015202530 frequency(khz) v in (v) MP2905- 3v to 28v input, hysteret ic synchronous step- down controller MP2905 rev. 0.91 www.monolithicpower.com 6 4/18/2011 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2011. all rights reserved. typical performanc e characteristics (continued) v in =12v, v out =1.8v, i out =12a, l1=1.5h, c out =100f *2+330f, t a =+25c, unless otherwise noted. fb peak and hysteresis start up and shut down by pull down and release ss short entry fb ovp short recovery v out 10v/div i inductor 10a/div external signal 1v/div ss 500mv/div 4ms/div v out 1v/div i inductor 10a/div sw 10v/div 20ms/div v out 1v/div i inductor 10a/div sw 10v/div 20ms/div fb 100mv/div sw 5v/div fb 100mv/div v out 1v/div hg 10v/div lg 5v/div 40ms/div v in power up i out =0a v out 1v/div v in 5v/div sw 10v/div i inductor 5a/div 1ms/div v in power off i out =0a v out 1v/div v in 5v/div sw 20v/div i inductor 5a/div v in power up i out =12a v out 1v/div v in 5v/div sw 10v/div i inductor 10a/div v in power off i out =12a v out 1v/div v in 5v/div sw 10v/div i inductor 10a/div 1ms/div 1ms/div 1s/div MP2905- 3v to 28v input, hysteret ic synchronous step- down controller MP2905 rev. 0.91 www.monolithicpower.com 7 4/18/2011 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2011. all rights reserved. typical performanc e characteristics (continued) v in =12v, v out =1.8v, i out =12a, l1=1.5h, c out =100f *2+330f, t a =+25c, unless otherwise noted. load transient response i out =6a~12a@1a/us 200us/div v out /ac 50mv/div i out 5a/div pre-bias test pre-bias output voltage=1.7v v out 500mv/div v in 5v/div 2ms/div output ripple voltage i out =0a, v out_ripple =18mv v out /ac 10mv/div sw 5v/div i inductor 2a/div load transient response i out =0a~12a@1a/us 200us/div 2us/div hg 10v/div lg 5v/div output ripple voltage i out =12a, v out_ripple =17.6mv v out /ac 20mv/div sw 5v/div i inductor 5a/div 2us/div v out /ac 100mv/div i out 5a/div MP2905- 3v to 28v input, hysteret ic synchronous step- down controller MP2905 rev. 0.91 www.monolithicpower.com 8 4/18/2011 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2011. all rights reserved. function diagram -- + -- + -- + -- + -- + shut down com ovp com loop comp 0.6v 0.75 0.05 ss r4=80k r3=84k r1 ref reg 1.23v bst reg nand or buf nor level shift down level shift up level shift down sw sw ref lg hg bst ilim in sw sw oc com buf bg r2 ref ss gnd fb figure 1?functional block diagram MP2905- 3v to 28v input, hysteret ic synchronous step- down controller MP2905 rev. 0.91 www.monolithicpower.com 9 4/18/2011 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2011. all rights reserved. operation MP2905 uses a hysteretic control loop to regulate output voltage. it senses the voltage at fb pin, which is compared with ss voltage with 20mv hysteresis. when fb is lower than ss 20mv, high side switch turns on and fb voltage rises up. after fb voltage reaches ss voltage, high side switch turns off and low side switch turns on, which cause fb voltage drop until fb is lower than ss 20mv. so vout is regulated at a stable voltage because fb voltage is regulated at the voltage (ss-10mv). see the setting output voltage for detailed information. hysteretic voltage-mode control provides fast transient response without additional loop compensation. soft-start an external cap is connected at ss pin to realize soft-start function. when ss pin pull down transistor turns off, internal reference begins to charge ss external cap through a resistor-divider. so fb rises slowly following ss voltage and inrush current is avoided. soft-start time is determined by external cap and internal resistor- divider. if ss has pre-bias voltage at startup, both hg and lg keep low, ss cap begins to discharge until lower than 50mv. then ss will rise slowly and fb tracks ss. startup sequence in MP2905, at startup, if fb>ss, which means output has pre-bias voltage, hg and lg don?t toggle until ss greater than fb. current limit function a resistor is connected from the drain of the high side mosfet to ilim pin to set current limit value. internal 50ua current sink from ilim to gnd limits the maximum vds cross high side switch drain and source. when vfb<300mv, if high side switch current hits the current limit, high side switch turns off immediately. if vfb>300mv, over current event occurs in four sequential cycles, high side switch turns off. once high side mosfet turns off, ss cap will be discharged by 250na current. after ss voltage is lower than 50mv, ss cap is stopped discharging and high side switch tries to turn on again. output over-voltage protection output over-voltage is monitored by fb voltage. if fb voltage higher than 750mv, hg is set low and lg is set high. this status will be latched until restart en or vin. enable MP2905 turns off by pulling down ss pin to lower than 50mv. releasing ss will start the run cycle. high side gate driver MP2905 doesn?t need schottky, but still needs 0.1uf bst cap between bst pin and sw pin. internal regulator most of the internal circuitries are powered from the 5v internal regulator (ref). this regulator takes v in input and operates in the full input range. when v in is greater than 5.0v, the output of the regulator is full regulation. when v in is lower than 5.0v, the output decreases. bypass ref pin to gnd with a 4.7uf or greater capacitor. under voltage lockout (uvlo) under-voltage lockout (uvlo) is implemented to protect the chip from operating at insufficient supply voltage. the MP2905 uvlo comparator monitors the output voltage of the internal regulator (ref). thermal protection the purpose of thermal protection is to prevent damage in the ic by allowing exceptive current to flow and heating the junction. the die temperature is internally monitored until the thermal limit is reached. once this temperature is reached, the part will be shut down and allow the chip to cool. when the ic is cool enough, the part will be turned on again. there is a built-in hysteresis. MP2905- 3v to 28v input, hysteret ic synchronous step- down controller MP2905 rev. 0.91 www.monolithicpower.com 10 4/18/2011 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2011. all rights reserved. application information setting the output voltage the external resistor divider is used to set the output voltage (see the schematic on front page). r1 is for approximately 50a to 150a bias current in the resistor-divider. a wide range of resistor r1 value is acceptable, choosing a typical value 6.04k, r3 is determined by: dc load fb vout 0.01v (r 0.5 i ) r3 r1 ( 1) v ++ = ? where v fb = 0.590v, r dc is the dc resistance of the output inductor, i load is the full load current, 0.5*i load is half load condition , it?s for load regulation standard. the term 0.01v is to reflect 1/2 of the feedback threshold hysteresis. but r3 value also can?t be too large, or circuit may work abnormally. selecting the inductor the inductor is required to supply constant current to the output load while being driven by the switched input voltage. a larger value inductor will is favorable to less ripple current and the lower output ripple voltage. however, the larger value inductor will have a larger physical size, higher series dc resistance, and/or lower saturation current. a good rule for determining the inductance to use is to allow the peak-to-peak ripple current in the inductor to be approximately 30% of the maximum switch current limit. also, make sure that the peak inductor current is below the maximum switch current limit. the inductance value can be calculated by: out out sl in vv l1 (1 ) fi v =? ? where v in is the input voltage, v out is the output voltage, f s is the switching frequency, and ? i l is the peak-to-peak inductor ripple current. choose an inductor that will not saturate under the maximum inductor peak current. the peak inductor current can be calculated by: out out lp load sin vv ii (1 ) 2f l1 v =+ ? where i load is the full load current. setting current limit MP2905 current limit can be set by an external resistor (r2) which is connected between ilim pin and the drain of the high side mosfet. an internal 50ua sink current sets a voltage drop on the resistor. the voltage drop compares to high-side mosfet voltage drop (vds) to set the peak current limit threshold. below is the diagram of current limit function: -- + -- + + -- i lim r ilim v in rdson_max high side switch oc com sw ids sw v+ v- figure 2?current limit functional diagram the voltage drop on the high side mosfet is: ds _ on ds ds _ on v ( max ) i ( max ) r ( max ) = where i ds (max) equals the max peak inductor current i lp (max). then, r ilim can be calculated using the v ds_on (max) with the following formula: ds _ on ilim v(max) r() 50ua = ? and r ilim should be kept in the range of 1k ? ~ 8k ? . selecting power mosfets the MP2905 connects two external, logic-level, n-channel mosfets as the circuit switching elements. the mosfets are the key points for circuit efficiency. the major parameters we should concern are: 1) on-resistance, r ds_on : the lower, the better it will be. 2) continuous drain current (@10sec), i d : it should be higher than the peak current @ full load condition. and pay attention to i d ?s variation with different temperature. MP2905- 3v to 28v input, hysteret ic synchronous step- down controller MP2905 rev. 0.91 www.monolithicpower.com 11 4/18/2011 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2011. all rights reserved. 3) maximum drain-to-source voltage, v ds (max): it should be at least 20% higher than the input supply rail at the high-side mosfet?s drain. 4) total gate charge qg: the lower, the better it will be. for high-side mosfet, the main power loss consists of conduction loss, switching loss, and drive loss. the high-side mosfet conduction loss can be calculated by: 2 high side _ conduction load highside _ dson pird ? = where d is the duct cycle, it?s defined by: out in v d v = high-side mosfet switching loss is calculated by: high side _ switching in load on off s 1 pvi(tt)f 2 ? =+ where t on is high-side mosfet turn on time, t off is high-side mosfet turn off time, f s is the switching frequency. high-side mosfet drive loss is calculated by: high side _ drive g _ high side s drive pqfv ?? = where vdrive is the high-side mosfet driving voltage, typical value is 5v. for low-side mosfet, there isn?t switching loss, conduction loss is the main loss, so we?d better choice a mosfet with lower rds-on than high side mosfet. the recommended rds-on of low side mosfet is one-third of high-side mosfet. the low-side mosfet loss consists of conduction loss, drive loss and body diode conduction loss. the low-side mosfet conduction loss is calculated by: 2 low side _ conduction load low side _ dson pir(1d) ?? = ? low-side mos drive loss is calculated by: low side _ drive g _ low side s drive pqfv ?? = body diode conduction loss is calculated by: bodydiode f load deadtime s p2vitf = where v f is body diode forward voltage drop, t deadtime is high-side mosfet and low-side mofets transition time. except the losses above, there still is output cap loss in both high side mosfet and low side mosfet. output cap loss is defined by: 2 cds ds ds s 1 pcvf 2 = where c ds is the output cap of mosfet. for less switching noise, add drive resistors in series with the gate of mosfet to slow down the transition between the high-side mosfet and low-side mosfet switching. selecting the feed forward capacitor the feed forward capacitor (c8 in front page typical application circuit) is a key factor to affect the frequency. it can be calculated by: 3 o fb s in fb fb in h fb v v 1 f(1) vv 1 rc8 v v (90ns 20ns ) c8 r r == ? +? where f s is desired the frequency, v fb is feedback reference voltage, typical is 590mv, v h is output regulation hysteresis, typical value is 22mv, r fb is the equivalent value of two voltage-divided resistors. for example, in 2905 typical application: fb r1 r3 r r1 r3 + = select an x7r ceramic capacitor with the closest capacitance to the value calculated as possible. increase the capacitance, the switching frequency decrease, and vice versa, decrease the capacitance, the frequency increase. and output capacitor, inductor and inductor dcr will affect the frequency, too, but those are limited. the frequency calculated by the formula has a deviation within 30%. setting the input capacitor the input current to the step-down converter is discontinuous, therefore a capacitor is required to supply the ac current to the step-down converter while maintaining the dc input voltage. use low esr capacitors for the best performance. ceramic capacitors with x5r or x7r dielectrics are highly recommended because of their low esr and small temperature coefficients. MP2905- 3v to 28v input, hysteret ic synchronous step- down controller MP2905 rev. 0.91 www.monolithicpower.com 12 4/18/2011 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2011. all rights reserved. since the input capacitor (cin) absorbs the input switching current, it requires an adequate ripple current rating. the rms current in the input capacitor can be estimated by: out out cin load in in vv ii (1 ) vv = ? the worse case condition occurs at v in = 2v out , where load cin i i 2 = for simplification, choose the input capacitor whose rms current rating greater than half of the maximum load current. the input capacitor can be electrolytic, tantalum or ceramic. when using electrolytic or tantalum capacitors, a small, high quality ceramic capacitor, i.e. 0.1f, should be placed as close to the ic as possible. when using ceramic capacitors, make sure that they have enough capacitance to provide sufficient charge to prevent excessive voltage ripple at input terminal. the input voltage ripple can be estimated by capacitance: load out out in sin in in iv v v(1) fc v v d= - setting the output capacitor the output capacitor (cout) is required to maintain the dc output voltage. ceramic, tantalum, or low esr electrolytic capacitors are recommended. low esr capacitors are preferred to keep the output voltage ripple low. the output voltage ripple can be estimated by: out out out esr sin sout vv 1 v(1)(r ) fl1 v 8fc d= - + where l is the inductor value and r esr is the equivalent series resistance (esr) value of the output capacitor. in the case of ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance. the output voltage ripple is mainly determined by the capacitance. for simplification, the output voltage ripple is: out out out 2 in sout vv v(1) v 8f l1c d= - in the case of tantalum or electrolytic capacitors, the esr dominates the impedance at the switching frequency. for simplification, the output ripple is: out out out esr sin vv v(1)r fl1 v d= - the characteristics of the output capacitor also affect the transient response and the stability of the regulation system. higher voltage ripple will influence the voltage of the feed forward capacitor to make the system be unstable. so, at the condition which the tantalum or electrolytic capacitors with higher esr is used or output current is higher, a rc filter is necessary from vout to gnd. connect the resistor of filter between the vout and feed forward capacitor, and connect the capacitor of filter from feed forward capacitor to gnd. follow the r7 and c12 connection in MP2905 typical application. 10 ? / 1uf or 2 ? / 4.4uf is recommended for good stability and better transient response. MP2905- 3v to 28v input, hysteret ic synchronous step- down controller MP2905 rev. 0.91 www.monolithicpower.com 13 4/18/2011 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2011. all rights reserved. typical application circuits figure 3?typical application circuits for 12a output figure 4?typical application circuits for 25a output without droop (7) note: 7) for 25a application design, please refer to mps special application note for 25a application. MP2905- 3v to 28v input, hysteret ic synchronous step- down controller MP2905 rev. 0.91 www.monolithicpower.com 14 4/18/2011 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2011. all rights reserved. pcb layout guide pcb layout is very important to achieve stable operation. it is highly recommended to duplicate evb layout for optimum performance. if change is necessary, please follow these guidelines: 1) keep the path of switching current short and minimize the loop area formed by input cap, high-side mosfet and low-side mosfet. 2) ic bypass ceramic capacitors are suggested to be put close to the in pin. 3) ensure all feedback connections are short and direct. place the feedback resistors as close to the chip as possible. 4) route sw away from sensitive analog areas such as fb. 5) connect in, sw, and especially gnd respectively to a large copper area to improve chip thermal performance and long term reliability. 6) it is suggested to add the snubber circuit across the high side mosfet (in pin and sw pin) so as to reduce the sw spike. 7) if output current is higher than 10a, recommend to use a four layers pcb, and pour ground in mid layer. figure 5?MP2905 application circuit MP2905- 3v to 28v input, hysteret ic synchronous step- down controller MP2905 rev. 0.91 www.monolithicpower.com 15 4/18/2011 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2011. all rights reserved. top layer in1 in2 bottom layer figure 6?MP2905 application circuit and pcb layout guide MP2905 ? product description in a #-pin package type notice: the information in this document is subject to change wi thout notice. please contact mps for current specifications. users should warrant and guarant ee that third party intellectual property right s are not infringed upon when integrating mps products into any application. mps will not assume any legal responsibility for any said applications. MP2905 rev. 0.91 www.monolithicpower.com 16 4/18/2011 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2011. all rights reserved. package information msop10 bottom view 0.030(0.75) 0.037(0.95) 0.043(1.10)max 0.002(0.05) 0.006(0.15) front view 0.004(0.10) 0.008(0.20) side view gauge plane 0.010(0.25) 0.016(0.40) 0.026(0.65) 0 o -6 o seating plane pin 1 id (note 5) 0.114(2.90) 0.122(3.10) 0.187(4.75) 0.199(5.05) 1 5 6 10 0.007(0.18) 0.011(0.28) 0.0197(0.50)bsc 0.114(2.90) 0.122(3.10) top view note: 1) control dimension is in inches. dimension in bracket is in millimeters. 2) package length does not include mold flash, protrusion or gate burr. 3) package width does not include interlead flash or protrusion. 4) lead coplanarity (bottom of leads after forming) shall be 0.004" inches max. 5) pin 1 identification has the half or full circle option. 6) drawing meets jedec mo-817, variation ba. 7) drawing is not to scale. recommended land pattern 0.012(0.30) 0.0197(0.50)bsc 0.181(4.60) 0.040(1.00) |
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