mp28117 dual 1.2mhz, 800ma synchronous step-down converter mp28117 rev.1.0 www.monolithicpower.com 1 12/13/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. the future of analog ic technology tm tm description the mp28117 contains two independent 1.2mhz constant frequency, current mode, pwm step-down converters. each converter integrates a main switch and a synchronous rectifier for high efficiency without an external schottky diode. the mp28117 is ideal for powering portable equipment that runs from a single cell lithium-ion (li+) battery. each converter can supply 800ma of load current from a 2.5v to 6v input voltage. the output voltage can be regulated as low as 0.6v. the mp28117 can also run at 100% duty cycle for low dropout applications. features ? up to 95% efficiency ? 1.2mhz constant switching frequency ? 800ma load current on each channel ? 2.5v to 6v input voltage range ? output voltage as low as 0.6v ? 100% duty cycle in dropout ? current mode control ? short circuit protection ? thermal fault protection ? <0.1 a shutdown current ? internally compensated ? space saving 10-pin qfn package applications ? cellular and smart phones ? microprocessors and dsp core supplies ? pdas ? mp3 players ? digital still and video cameras ? portable instruments ?mps? and ?the future of analog ic technology? are trademarks of monolithic power systems, inc. typical application mp28117 in2 in1 3 8 4 9 gnd2 gnd1 fb2 sw2 en2 7 5 6 2 10 1 fb1 sw1 en1 v in1/in2 2.5v to 6v off on off on v out2 1.2v 800ma v out1 1.8v 800ma 100 95 90 85 80 75 70 65 60 55 50 efficiency ( % ) 0 500 1000 load current (ma) v out =3.3v
mp28117 ? dual 1.2mhz 800ma synchronous step-down converter mp28117 rev.1.0 www.monolithicpower.com 2 12/13/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. tm package reference part number* package temperature mp28117dq qfn10 (3mm x 3mm) ?40 c to +85 c * for tape & reel, add suffix ?z (eg. mp28117dq?z) for rohs compliant packaging, add suffix ?lf (eg. mp28117dq?lf?z) absolute maxi mum ratings (1) v in1/in2 to gnd ............................ ?0.3v to +6.5v v sw1/sw2 to gnd................... ?0.3v to v in + 0.3v v fb1/fb2 , v en1/en2 to gnd ............. ?0.3v to +6.5v junction temperature.............................+150 c lead temperature ..................................+260 c storage temperature .............?65 c to +150 c recommended operating conditions (2) supply voltage v in1/in2 ....................... 2.5v to 6v output voltage v out1/out2 .................. 0.6v to 6v operating temperature .............?40 c to +85 c thermal resistance (3) ja jc qfn10 (3mm x 3mm) ............. 50 ...... 12... c/w notes: 1) exceeding these ratings may damage the device. 2) the device is not guaranteed to function outside of its operating conditions. 3) measured on approximately 1? square of 1 oz copper. electrical characteristics (4) v in1/in2 = v en1/en2 = 3.6v, t a = +25 c, unless otherwise noted. parameter symbol condition min typ max units each converter supply current v en1/en2 = v in1/in2 , v fb1/fb2 = 0.65v 440 600 a each converter shutdown current v en1/en2 = 0v, v in1/in2 = 6v 0.10 1 a in under voltage lockout threshold rising edge 2.15 2.30 2.40 v in under voltage lockout hysteresis 55 mv t a = +25c 0.588 0.600 0.612 regulated fb voltage v fb ?40c t a +85c 0.582 0.600 0.618 v fb input bias current i fb v fb1/fb2 = 0.65v ?50 0.5 +50 na pfet on resistance i sw1/sw2 = 100ma 0.42 ? nfet on resistance i sw1/sw2 = ?100ma 0.26 ? sw leakage current v en1/en2 = 0v, v in1/in2 = 6v v sw1/sw2 = 0v or 6v ?2 +2 a pfet current limit duty cycle = 100%, current pulse width < 1ms 0.9 1.3 1.8 a oscillator frequency f osc 0.99 1.24 1.49 mhz thermal shutdown trip threshold 150 c en enable threshold ?40c t a +85c 0.3 0.96 1.5 v en input current v en1/en2 = 0v to 6v ?1 +1 a notes: 4) production test at +25c. specificat ions over the temperature range are guaranteed by design and characterization. top view en1 fb1 in2 gnd2 sw2 1 2 3 4 5 sw1 gnd1 in1 fb2 en2 10 9 8 7 6 exposed pad on backside
mp28117 ? dual 1.2mhz 800ma synchronous step-down converter mp28117 rev.1.0 www.monolithicpower.com 3 12/13/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. tm typical performanc e characteristics v in1/in2 = 3.3v, v out1 = 1.8v, v out2 = 1.2v, l 1/2 = 4.7 h, c in1/in2 = 4.7 f, c out1/out2 = 10 f, t a = +25 c, unless otherwise noted. short circuit protection (no load) short circuit recovery (no load) startup from shutdown v out 1v/div i l 0.5a/div v out 1v/div i l 0.5a/div v en 2v/div v out 1v/div i l 0.5a/div 400ns/div load transient (i out =0ma to 500ma step) medium load operation (i out =400ma) v out ac 100mv/div. i load 0.5a/div. i l 0.5a/div. v sw 2v/div. v out ac 20mv/div. i l 200ma/div. v sw 2v/div. v out ac 20mv/div. i l 500ma/div. 400ns/div heavy load operation (i out =800ma) 0.606 0.604 0.602 0.600 0.598 0.596 0.594 feedback voltage (v) -40 +20 0 -20 +40 +60 +80 +100 temperature ( c) feedback voltage vs temperature 100 90 80 70 60 50 efficiency (%) 0.0 0.4 0.2 0.6 0.8 load current (a) efficiency vs load current v out1 =1.8v v out2 =1.2v
mp28117 ? dual 1.2mhz 800ma synchronous step-down converter mp28117 rev.1.0 www.monolithicpower.com 4 12/13/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. tm pin functions pin # name description 1 en1 channel 1 enable control input. drive en1 above 1.5v to turn on the channel 1. drive en1 below 0.3v to turn it off (shutdown current < 0.1 a). 2 fb1 channel 1 feedback input. connect fb1 to the center point of the external resistor divider. the feedback voltage is 0.6v. 3 in2 channel 2 supply input. bypass to gnd with a 2.2 f or greater ceramic capacitor. 4 gnd2 ground 2. 5 sw2 channel 2 power switch output. inductor connection to drains of the internal pfet and nfet switches. 6 en2 channel 2 enable control input. drive en2 above 1.5v to turn on the channel 2. drive en2 below 0.3v to turn it off (shutdown current < 0.1 a). 7 fb2 channel 2 feedback input. connect fb2 to the center point of the external resistor divider. the feedback voltage is 0.6v. 8 in1 channel 1 supply input. bypass to gnd with a 2.2 f or greater ceramic capacitor. 9 gnd1 ground 1. 10 sw1 channel 1 power switch output. inductor connection to drains of the internal pfet and nfet switches.
mp28117 ? dual 1.2mhz 800ma synchronous step-down converter mp28117 rev.1.0 www.monolithicpower.com 5 12/13/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. tm operation in1/ in2 en1/ en2 fb1/ fb2 gnd1/ gnd2 sw1/ sw2 + + -- pwmcmp pwm osc + -- eamp ics slope comp feedback error\ amp 0.6v eao cc 17pf bias & voltage reference pwm control logic 1.0mhz oscillator iamp 10x current sense amp dh dl + -- main switch (pch) synchronous rectifier (nch) figure 1?functional block diagram (diagram represents ? of the mp28117) the mp28117 has dual independent constant frequency current mode pwm step-down converters. the mp28117 is optimized for low voltage, li-ion battery powered applications where high efficiency and small size are critical. the mp28117 uses external resistor dividers to set two output voltages independently from 0.6v to 6v. the device integrates both main switches and synchronous rectifiers, which provides high efficiency and eliminates the need for an external schottky diode. the mp28117 can achieve 100% duty cycle. the duty cycle d of each step-down converter is defined as: % 100 v v % 100 f t d in out osc on = = where t on is the main switch on time, f osc is the oscillator frequency (1.2mhz), v out is the output voltage and v in is the input voltage. current mode pwm control slope compensated current mode pwm control provides stable switching and cycle-by-cycle current limit for superior load and line response and protection of the internal main switch and synchronous rectifier. each channel switches at a constant frequency (1.2mhz) and regulates the output voltage. during each cycle the pwm comparator modulates the power transferred to the load by changing the inductor peak current based on the feedback error voltage. during normal operation, the main switch is turned on for a certain time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when the peak inductor current is above the error voltage. when the main switch is off, the synchronous rectifier will be turned on immediately and stay on until the next cycle starts.
mp28117 ? dual 1.2mhz 800ma synchronous step-down converter mp28117 rev.1.0 www.monolithicpower.com 6 12/13/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. tm dropout operation each channel of the mp28117 allows the main switch to remain on for more than one switching cycle and increases the duty cycle while the input voltage is dropping close to the output voltage. when the duty cycle reaches 100%, the main switch is held on continuously to deliver current to the output up to the pfet current limit. the output voltage then is the input voltage minus the voltage drop across the main switch and the inductor. short circuit protection the mp28117 has short circuit protection. when any output is shorted to ground, the oscillator frequency is reduced to prevent the inductor current from increasing beyond the pfet current limit. the pfet current limit is also reduced to lower the short circuit current. the frequency and current limit will return to the normal values once the short circuit condition is removed and the feedback voltage reaches 0.6v. maximum load current the mp28117 can operate down to 2.5v input voltage, however the maximum load current decreases at lower input due to large ir drop on the main switch and synchronous rectifier. the slope compensation signal reduces the peak inductor current as a function of the duty cycle to prevent sub-harmonic oscillations at duty cycles greater than 50%. conversely the current limit increases as the duty cycle decreases. application information output voltage setting the external resistor divider sets the output voltage. the feedback resistor r1 also sets the feedback loop bandwidth with the internal compensation capacitor (see figure 1). choose r1 around 300k ? for optimal transient response. r2 is then given by: 1 v 6 . 0 v 1 r 2 r out ? = table 1?resistor selection vs. output voltage setting v out r1 r2 1.2v 300k ? (1%) 300k ? (1%) 1.5v 300k ? (1%) 200k ? (1%) 1.8v 300k ? (1%) 150k ? (1%) 2.5v 300k ? (1%) 95.3k ? (1%) inductor selection a 1 h to 10 h inductor with dc current rating at least 25% higher than the maximum load current is recommended for most applications. for best efficiency, the inductor dc resistance shall be <200m ? . see table 2 for recommended inductors and manufacturers. 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 inductor ripple current. choose inductor ripple current approximately 30% of the maximum load current, 800ma. 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. table 3 lists inductors recommended for this purpose.
mp28117 ? dual 1.2mhz 800ma synchronous step-down converter mp28117 rev.1.0 www.monolithicpower.com 7 12/13/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. tm table 2?suggested surface mount inductors manufacturer part number inductance ( h) max dcr ( ? ) saturation current (a) dimensions lxwxh (mm 3 ) coilcraft lp03310-222ml 2. 2 0.15 1.1 3.3 x 3.3 x 1 toko 1002as 2.2 0.11 1.14 4.6 x 4.6 x 1.2 sumida cdrh3d16 2.2 0.072 1.20 4 x 4 x 1.8 table 3?inductors for improved efficiency at 25ma, 50ma, under 100ma load. manufacturer part number inductance ( h) max dcr ( ? ) saturation current (a) i rms (a) coilcraft do1605t-103mx 10 0.3 1.0 0.9 murata lqh4c100k04 10 0.2 1.2 0.8 sumida cr32-100 10 0.2 1.0 0.7 sumida cr54-100 10 0.1 1.2 1.4 input capacitor selection the input capacitor reduces the surge current drawn from the input and switching noise from the device. the input capacitor impedance at the switching frequency shall be less than input source impedance to prevent high frequency switching current passing to the input. ceramic capacitors with x5r or x7r dielectrics are highly recommended because of their low esr and small temperature coefficients. for most applications, a 4.7 f capacitor is sufficient. output capacitor selection the output capacitor keeps output voltage ripple small and ensures regulation loop stable. the output capacitor impedance shall be low at the switching frequency. ceramic capacitors with x5r or x7r dielectrics are recommended. the output ripple v out is approximately: () ? ? ? ? ? ? ? ? + ? 3 c f 8 1 esr l f v v v v v osc osc in out in out out thermal dissipation power dissipation shall be considered when both channels of the mp28117 provide maximum 800ma output current to the loads at high ambient temperature with low input supply voltage. if the junction temperature rises above 150 c, the mp28117 two channels will be shut down. the junction-to-ambient thermal resistance of the 10-pin qfn (3mm x 3mm) r ja is 50 c/w. the maximum power dissipation is about 1.6w when the mp28117 is operating in a 70 c ambient temperature environment. w 6 . 1 w / c 50 c 70 c 150 pd o o o max = ? = pc board layout the high current paths (gnd1/gnd2, in1/in2 and sw1/sw2) should be placed very close to the device with short, direct and wide traces. input capacitors should be placed as close as possible to the respective in and gnd pins. the external feedback resistors shall be placed next to the fb pins. keep the switching nodes sw1/sw2 short and away from the feedback network.
mp28117 ? dual 1.2mhz 800ma synchronous step-down converter notice: the information in this document is subject to change wi thout notice. users should warra nt and guarantee that third party intellectual property rights are not infringed upon w hen integrating mps products into any application. mps will not assume any legal responsibility for any said applications. mp28117 rev. 1.0 www.monolithicpower.com 8 12/13/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. tm package information qfn10 (3mm x 3mm) side view top view 1 10 6 5 bottom view 2.90 3.10 1.45 1.75 2.90 3.10 2.25 2.55 0.50 bsc 0.18 0.30 0.80 1.00 0.00 0.05 0.20 ref pin 1 id marking 1.70 0.50 0.25 recommended land pattern 2.90 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 conforms to jedec mo-229, variation veed-5. 5) drawing is not to scale. pin 1 id see detail a 2.50 0.70 pin 1 id option b r0.20 typ. pin 1 id option a r0.20 typ. detail a 0.30 0.50 pin 1 id index area
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