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mp8642 dual 3a, 23v, 600khz s tep-down converter with frequency synchronization mp8642 rev. 1.0 www.monolithicpower.com 1 9/13/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. the future of analog ic technology description the mp8642 is a dual monolithic step-down switch mode converter with built-in internal power mosfets. it achieves 3a continuous output current for each output over a wide input supply range with excellent load and line regulation. current mode operation provides fast transient response and eases loop stabilization. fault condition protection includes cycle-by-cycle current limiting and thermal shutdown. the mp8642 requires a minimum number of readily available standard external components. features ? 3a current for each output ? 80m ? internal power mosfet switch ? stable with low esr output ceramic capacitors ? up to 95% efficiency ? power good indicator ? fixed 600khz frequency ? synchronizable to >1mhz external clock ? thermal shutdown ? cycle-by-cycle over current protection ? wide 4.5v to 23v operating input range ? each output adjustable from 0.8v to 20v ? available in a 5mm x 5mm 32-pin qfn package applications ? point of load regulator in distributed power systems ? digital set top boxes ? personal video recorders ? broadband communications ? flat panel television and monitors all mps parts are lead-free and adhere to the rohs directive. for mps green status, please visit mps website under products, quality assurance page. ?mps? and ?the future of analog ic technology? are registered trademarks of monolithic power systems, inc. typical application mp8642 25,26,27 14 17 18 15 19 12,13 8 16 gnd1 gnd2 bst1 in1 in2 sw1 bg1 fb1 pg1 vcc1 en/sync1 bst2 sw2 bg2 fb2 pg2 vcc2 en/sync2 5 29,30,31 21,22,23,24 1,2,3,4 7 10 6 9 11 v out2 2.5v@3a m3 v in v out1 off on m2 v cc v cc on off
mp8642 ? dual 3a, 23v, 600khz step-down converter mp8642 rev. 1.0 www.monolithicpower.com 2 9/13/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. ordering information part number* package top marking free air temperature (t a ) MP8642DU qfn32 (5mm x5mm) m8642du ?40 ? c to +85 ? c * for tape & reel, add suffix ?z (e.g. mp MP8642DU?z); for rohs compliant packaging, add suffix ?lf; (e.g. MP8642DU?lf?z) package reference in2 n/c in1 in1 in1 n/c sw2 sw2 sw2 in2 in2 n/c en/sync2 pg2 fb2 in2 sw1 en/sync1 pg1 fb1 gnd2 gnd2 bg2 vcc2 bst2 sw1 sw1 bst1 vcc1 bg1 gnd1 sw1 1 2 3 4 5 6 7 8 24 23 22 21 20 19 18 17 910111213141516 32 31 30 29 28 27 26 25 absolute maxi mum ratings (1) supply voltage v in ....................................... 25v v sw .........................-0.3v(-5v for < 10ns) to 26v v bs ....................................................... v sw + 6v all other pins .................................?0.3v to +6v continuous power dissipation (t a = +25c) (2) ........................................................... 3.47w junction temperature ...............................150 ? c lead temperature ....................................260 ? c storage temperature.............. ?65 ? c to +150 ? c recommended operating conditions (3) supply voltage v in ...........................4.5v to 23v output voltage v out .........................0.8v to 20v operating junct. temp (t j )..... ?40 ? c to +125 ? c thermal resistance (4) ja jc 5x5 qfn32 ????????36???8? ? 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 continuous power dissipation at any ambient temperature is calculated by p d (max) = (t j (max)-t a )/ ja . exceeding the maximum allowable powe r dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. internal thermal shutdown circuitry protects the device from permanent damage. 3) the device is not guaranteed to function outside of its operating conditions. 4) measured on jesd51-7, 4-layer pcb.
mp8642 ? dual 3a, 23v, 600khz step-down converter mp8642 rev. 1.0 www.monolithicpower.com 3 9/13/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. electrical characteristics v in = 12v, t a = +25 ? c, unless otherwise noted. parameters symbol condition min typ max units feedback voltage v fb 4.5v ? v in ? 23v 0.788 0.808 0.828 v feedback current i fb v fb = 0.8v 10 na switch on resistance (5) r ds(on) 80 m ? switch leakage v en = 0v, v sw = 0v 0.1 10 a current limit (5) 4 a oscillator frequency f sw v fb = 0.6v 400 600 800 khz fold-back frequency v fb = 0v 60 150 240 khz maximum duty cycle v fb = 0.6v 85 90 % minimum on time (4) t on 100 ns under voltage lockout threshold rising 3.9 4.1 4.3 v under voltage lockout threshold hysteresis 880 mv en input low voltage 0.4 v en input high voltage 1.5 v v en = 2v 2 en input current v en = 0v 0.1 a supply current (shutdown) v en = 0v 0.1 10 a supply current (quiescent) v en = 2v, v fb = 1v 0.9 1.1 ma thermal shutdown 150 c bg driver bias supply voltage v cc 4.5 5 v gate driver sink impedance (5) r sink 1 2 ? gate driver source impedance (5) r source 4 5.5 ? gate drive current sense trip threshold 20 mv power good threshold 0.69 0.74 0.79 v power good threshold hysteresis 40 mv pg pin level v pg pg sink 4ma 0.4 v note: 5) guaranteed by design.
mp8642 ? dual 3a, 23v, 600khz step-down converter mp8642 rev. 1.0 www.monolithicpower.com 4 9/13/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. pin functions pin # name description 1, 2, 3, 4 sw1 switch output channel 1 5 bst1 bootstrap channel 1. this capacitor is needed to drive the power switch?s gate above the supply voltage. it is connected between sw1 and bst1pins to form a floating supply across the power switch driver. 6 vcc1 bg driver bias supply channel 1. decouple with a 1f ceramic capacitor. 7 bg1 gate driver output channel 1. connec t this pin to the synchronous mosfet gate 8 gnd1 ground channel 1. 9 en/sync1 on/off control and external fr equency synchronization input channel 1. 10 pg1 power good indicator channel 1. connect this pin to vcc or vout by a 100k ? pull-up resistor. the output of this pin is low if the output voltage is 10% less than the nominal voltage, otherwise it is an open drain. 11 fb1 feedback channel 1. an external resistor divi der from the output1 to gnd1, tapped to the fb1 pin sets the output voltage. to prevent current limit r un away during a short circuit fault condition the frequency foldback compar ator lowers the oscillator frequency when the fb voltage is below 250mv. 12, 13 gnd2 ground channel 2. 14 bg2 gate driver output channel 2. connec t this pin to the synchronous mosfet gate 15 vcc2 g driver bias supply channel 2. decouple with a 1f ceramic capacitor. 16 bst2 bootstrap channel 2. this capacitor is neede d to drive the power switch?s gate above the supply voltage. it is connected between sw2 and bst2 pins to form a floating supply across the power switch driver. 17 fb2 feedback channel 2. an external resistor divi der from the output2 to gnd2, tapped to the fb2 pin sets the output voltage. to prevent current limit r un away during a short circuit fault condition the frequency foldback compar ator lowers the oscillator frequency when the fb voltage is below 250mv. 18 pg2 power good indicator channel 2. connect this pin to v cc or v out by a 100k ? pull-up resistor. the output of this pin is low if the output voltage is 10% less than the nominal voltage, otherwise it is an open drain. 19 en/sync2 on/off control and external fr equency synchronization input channel 2. 20, 28, 32 n/c no connect 21, 22, 23, 24 in2 supply voltage channel 2. the mp8642 operates from a +4.5v to +23v unregulated input. 25, 26, 27 sw2 switch output channel 2 29, 30, 31 in1 supply voltage channel 1. the mp8642 operates from a +4.5v to +23v unregulated input.
mp8642 ? dual 3a, 23v, 600khz step-down converter mp8642 rev. 1.0 www.monolithicpower.com 5 9/13/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical performanc e characteristics v in = 12v, v out = 3.3v, l =3.9h, t a = +25oc, unless otherwise noted. d max limit 820 825 830 835 840 845 850 855 860 865 870 0 5 10 15 20 25 0 5 10 15 20 25 0 5 10 15 20 25 0 5 10 15 20 25 0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 4.0 4.5 5.0 5.5 6.0 6.5 7.0 0 20406080100 -0.07 -0.05 -0.03 -0.01 0.01 0.03 0.05 0.07 00.511.522.533.5 peak current (a) duty cycle (%) peak current vs. duty cycle input voltage (v) output current (a) line regulation i out =5a case temperature vs. output current load current (a) load regulation v in =12v output voltage (v) input voltage (v) operating range v cc (v) v cc regulator line regulation 0.1 1 10 100 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 input voltage (v) input voltage (v) input voltage (v) enable supply current vs. input voltage disable supply current vs. input voltage -0.10 -0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0369121518212427 30.0 32.5 35.0 37.5 40.0 42.5 45.0 0.5 1 1.5 2 2.5 3
mp8642 ? dual 3a, 23v, 600khz step-down converter mp8642 rev. 1.0 www.monolithicpower.com 6 9/13/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical performance characteristics ( continued ) v in = 12v, v out = 3.3v, l =3.9h, t a = +25oc, unless otherwise noted. v out 2v/div v sw 10v/div v out 2v/div v in 10v/div v in /ac 100mv/div v sw 10v/div i inductor 2a/div v sw 10v/div v out /ac 100mv/div v out /ac 20mv/div v sw 10v/div i inductor 2a/div i load 2a/div i inductor 2a/div v out 2v/div v en 5v/div v sw 10v/div i inductor 5a/div v out 2v/div v en 5v/div v sw 10v/div v sw 5v/div i inductor 5a/div v in 10v/div v out 2v/div v sw 10v/div i inductor 2a/div
mp8642 ? dual 3a, 23v, 600khz step-down converter mp8642 rev. 1.0 www.monolithicpower.com 7 9/13/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. operation in1/in2 en/sync1/ en/sync2 fb1/fb2 regulator oscillator 600khz driver current sense amplifier x40 error amplifier current limit comparator pwm comparator driver regulator reference -- + -- + -- + s r r q q -- + c1 50pf c1 1pf power good v bg v cc v cc v bg figure 1?functional block diagram (diagram portrays ? of the mp8642) the mp8642 is a dual channel, fixed frequency, synchronous, step-down switching regulator with integrated high-side power mosfets and gate drivers for a low-side external mosfets. it achieves 3a continuous output current for each output over a wide input supply range with excellent load and line regulation in each channel. it provides a single highly efficient solution with current mode control for fast loop response and easy compensation. the mp8642 operates in a fixed frequency, peak current control mode to regulate the output voltage. on each channel, a pwm cycle is initiated by the internal clock. the integrated high-side power mosfet is turned on and remains on until its current reaches the value set by the comp voltage. when the power switch is off, it remains off until th e next clock cycle starts. if, in 90% of one pwm period, the current in the power mosfet does not reach the comp set current value, the power mosfet will be forced to turn off. error amplifier the error amplifier compares the fb pin voltage with the internal 0.8v reference (ref) and outputs a current proportional to the difference between the two. this output current is then used to charge or discharge the internal compensation network to form the comp voltage, which is used to control the power mosfet current. the optimized internal compensation network minimizes the external component counts and simplifies the control loop design. internal regulator most of the internal circuitries are powered from the 5v internal regulator. this regulator takes the vin input and operates in the full vin range. when vin is greater than 5.0v, the output of the regulator is in full regulation. when vin is lower than 5.0v, the output decreases. since this internal regulator provides the bias current for the bottom gate driver that requires significant amount of current depending upon the external mosfet selection, a 1uf ceramic capacitor for decoupling purpose is required.
mp8642 ? dual 3a, 23v, 600khz step-down converter mp8642 rev. 1.0 www.monolithicpower.com 8 9/13/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. enable/synch control the mp8642 has a dedicated enable/synch control pin (en/sync) on each channel. by pulling it high or low, the ic can be enabled and disabled by en. tie en to vin for automatic start up. to disable the part, en must be pulled low for at least 5s. the mp8642 can be synchronized to external clock range from 300khz up to 1.4mhz through the en/sync pin. the internal clock rising edge is synchronized to the external clock rising edge. under-voltage lockout (uvlo) under-voltage lockout (uvlo) is implemented to protect the chip from operating at insufficient supply voltage. the mp8642 uvlo comparator monitors the output voltage of the internal regulator, vcc. the uvlo rising threshold is about 4.1v while its falling threshold is a consistent 3.2v. internal soft-start the soft-start is implemented to prevent the converter output voltage from overshooting during startup. when the chip starts, the internal circuitry generates a soft-start voltage (ss) ramping up from 0v to 1.2v. when it is lower than the internal reference (ref), ss overrides ref so the error amplifier uses ss as the reference. when ss is higher than ref, ref regains control. over-current-protection (ocp) the mp8642 has cycle-by-cycle over current limit when the inductor current peak value exceeds the set current limit threshold. meanwhile, output voltage starts to drop until fb is below the under-voltage (uv) threshold, typically 30% below the reference. once a output uv is triggered, the mp8642 enters latch off mode. mode is especially useful to ensure system safety under fault condition. the mp8642 exits the latch off mode once the en or input power is re-cycled. thermal shutdown thermal shutdown is implemented to prevent the chip from operating at exceedingly high temperatures. when the silicon die temperature is higher than 150 ? c, it shuts down the whole chip. when the temperature is lower than its lower threshold, typically 140 ? c, the chip is enabled again. floating driver and bootstrap charging the floating power mosfet driver is powered by an external bootstrap capacitor. this floating driver has its own uvlo protection. this uvlo?s rising threshold is 2.2v with a hysteresis of 150mv. the bootstrap capacitor voltage is regulated internally by v in through d1, m3, c4, l1 and c2 (figure 2). if (v in -v sw ) is more than 5v, u2 will regulate m3 to maintain a 5v bst voltage across c4. -- + -- + v in 5v u2 d1 m3 bst sw c4 c2 l1 v out figure 2 ? internal bootstrap charging circuit startup and shutdown if both vin and en are higher than their appropriate thresholds, the chip starts. the reference block starts first, generating stable reference voltage and currents, and then the internal regulator is enabled. the regulator provides stable supply for the remaining circuitries. three events can shut down the chip: en low, vin low and thermal shutdown. in the shutdown procedure, the signaling path is first blocked to avoid any fault triggering. the comp voltage and the internal supply rail are then pulled down. the floating driver is not subject to this shutdown command.
mp8642 ? dual 3a, 23v, 600khz step-down converter mp8642 rev. 1.0 www.monolithicpower.com 9 9/13/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. application information component selection the mp8642 has two channels: 1 and 2. the following formulas are used for component selection of both channels. setting the output voltage the external resistor divider is used to set the output voltage (see the schematic on front page). the feedback resistor r1 also sets the feedback loop bandwidth with the internal compensation capacitor (see figure 1). choose r1 to be around 40.2k ? for optimal transient response. r2 is then given by: 1 v 8 . 0 v 1 r 2 r out ? ? table 1?resistor selection for common output voltages v out (v) r1 (k ? ) r2 (k ? ) 1.8 40.2 (1%) 32.4 (1%) 2.5 40.2 (1%) 19.1 (1%) 3.3 40.2 (1%) 13 (1%) 5 40.2 (1%) 7.68 (1%) selecting the inductor a 1h to 10h inductor with a dc current rating of at least 25% percent higher than the maximum load current is recommended for most applications. for highest efficiency, the inductor dc resistance should be less than 15m ? . for most designs, the inductance value can be derived from the following equation. osc l in out in out f i v ) v v ( v l ? ? ? ? ? ? where i l is the inductor ripple current. choose inductor current to be approximately 30% if the maximum load current, 3a. the maximum inductor peak current is: 2 i i i l load ) max ( l ? ? ? under light load conditions below 100ma, larger inductance is recommended for improved efficiency. synchronous mosfet the external synchronous mosfet is used to supply current to the inductor when the internal high-side switch is off. it reduces the power loss significantly when compared against a schottky rectifier. table 2 lists example synchronous mosfets and manufacturers. table 2?synchronous mosfet selection guide part no. manufacture si7112 v ishay si7114 v ishay am4874 analog power selecting 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. for most applications, a 10f capacitor is sufficient. since the input capacitor (c1) absorbs the input switching current it requires an adequate ripple current rating. the rms current in the input capacitor can be estimated by: ? ? ? ? ? ? ? ? ? ? ? ? in out in out load 1 c v v 1 v v i i the worse case condition occurs at v in = 2v out , where: 2 i i load 1 c ? for simplification, choose the input capacitor whose rms current rating greater than half of the maximum load current.
mp8642 ? dual 3a, 23v, 600khz step-down converter mp8642 rev. 1.0 www.monolithicpower.com 10 9/13/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. the input capacitor can be electrolytic, tantalum or ceramic. when using electrolytic or tantalum capacitors, a small, high quality ceramic capacitor, i.e. 0.1 f, 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. the input voltage ripple caused by capacitance can be estimated by: ? ? ? ? ? ? ? ? ? ? ? ? ? ? in out in out s load in v v 1 v v 1 c f i v selecting the output capacitor the output capacitor (c2) 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: ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 2 c f 8 1 r v v 1 l f v v s esr in out s out out 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 caused by the capacitance. for simplification, the output voltage ripple can be estimated by: ? ? ? ? ? ? ? ? ? ? ? ? ? ? in out 2 s out out v v 1 2 c l f 8 v v in the case of tantalum or electrolytic capacitors, the esr dominates the impedance at the switching frequency. for simplification, the output ripple can be approximated to: esr in out s out out r v v 1 l f v v ? ? ? ? ? ? ? ? ? ? ? ? ? the characteristics of the output capacitor also affect the stability of the regulation system. the mp8642 can be optimized for a wide range of capacitance and esr values. pcb layout guide pcb layout is very important to achieve stable operation. please follow these guidelines and take figure3 for references. 1) keep the path of switching current short and minimize the loop area formed by input cap, high-side and low-side mosfets. 2) keep the connection of low-side mosfet between sw pin and input power ground as short and wide as possible. 3) ensure all feedback connections are short and direct. place the feedback resistors and compensation components 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 cool the chip to improve thermal performance and long-term reliability. top layer
mp8642 ? dual 3a, 23v, 600khz step-down converter mp8642 rev. 1.0 www.monolithicpower.com 11 9/13/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. bottom layer figure 3?pcb layout external bootstrap diode an external bootstrap diode may enhance the efficiency of the regulator, the applicable conditions of external bst diode are: ? v out =5v or 3.3v; and ? duty cycle is high: d= in out v v >65% in these cases, an external bst diode is recommended from the output of the voltage regulator to bst pin, as shown in fig.4 mp8642 sw bst c l bst c 5v or 3.3v out external bst diode in4148 + figure 4?add optional external bootstrap diode to enhance efficiency the recommended external bst diode is in4148, and the bst cap is 0.1~1f.
mp8642 ? dual 3a, 23v, 600khz step-down converter notice: the information in this document is subject to change wi thout notice. please contact m ps for current specifications. users should warrant and guarantee that third party intellectual property rights ar e not infringed upon when integrating mps products into any application. mps will not assume any legal responsibility for any said applications. mp8642 rev. 1.0 www.monolithicpower.com 12 9/13/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. package information 5mm x 5mm qfn32 side view top view 1 32 25 24 17 16 9 8 bottom view 4.90 5.10 3.50 3.80 4.90 5.10 3.50 3.80 0.50 bsc 0.18 0.30 0.80 1.00 0.00 0.05 0.20 ref pin 1 id marking 3.70 0.25 recommended land pattern 4.90 note: 1) all dimensions are in millimeters. 2) exposed paddle size does not include mold flash. 3) lead coplanarity shall be 0.10 millimeter max. 4) drawing confirms to jedec mo-220, variation vhhc-2. 5) drawing is not to scale. pin 1 id see detail a pin 1 id option a 0.30x45 o typ. pin 1 id option b r0.25 typ. detail a pin 1 id index area 0.70 0.35 0.45 0.50

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