mp2105 1mhz, 800ma synchronous step-down converter mp2105 rev. 1.2 www.monolithicpower.com 1 8/19/2005 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2005 mps. all rights reserved. the future of analog ic technology tm tm description the mp2105 is a 1mhz constant frequency, current mode, pwm step-down converter. the device integrates a main switch and a synchronous rectifier for high efficiency without an external schottky diode. it is ideal for powering portable equipment that runs from a single cell lithium-ion (li+) battery. the mp2105 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 mp2105 can also run at 100% duty cycle for low dropout applications. the mp2105 is available in a low profile (1mm) 5-pin, tsot package. evaluation board reference board number dimensions ev2105dj-00a 2.0?x x 2.0?y x 0.5?z features ? high efficiency: up to 95% ? 1mhz constant switching frequency ? 800ma available load current ? 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 ? <0.1a shutdown current ? space saving 5-pin tsot23 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 mp2105 sw fb 3 5 en gnd 2 in 1 4 output 1.8v 800ma input 2.5v to 6v mp2105_tac_s01 off on 100 90 80 70 60 50 40 30 20 10 0 efficiency (%) 10 100 1000 load current (ma) mp2105-ec01 efficiency vs load current v in = 3.3v v in = 4.2v
mp2105 ? 1mhz 800ma synchronous step-down converter mp2105 rev. 1.2 www.monolithicpower.com 2 8/19/2005 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2005 mps. all rights reserved. tm package reference part number* package temperature MP2105DJ tsot23-5 ?40 c to +85 c * for tape & reel, add suffix ?z (eg. MP2105DJ?z) for lead free, add suffix ?lf (eg. MP2105DJ?lf?z) absolute maxi mum ratings (1) v in to gnd .................................. ?0.3v to +6.5v v sw to gnd........................... ?0.3v to v in +0.3v v fb , v en 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 in ............................. 2.5v to 6v output voltage v out .......................... 0.6v to 6v operating temperature .............?40 c to +85 c thermal resistance (3) ja jc tsot23-5.............................. 220 .... 110.. 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 in = v en = 3.6v, t a = +25 c, unless otherwise noted. parameter symbol condition min typ max units supply current v en = v in , v fb = 0.65v 440 600 a shutdown current v en = 0v, v in = 6v 0.10 1 a in undervoltage lockout threshold rising edge 2.15 2.30 2.40 v in undervoltage 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 v fb = 0.65v ?50 0.5 +50 na pfet on resistance i sw = 100ma 0.42 ? nfet on resistance i sw = ?100ma 0.26 ? sw leakage current v en = 0v, v in = 6v, v sw = 0v or 6v ?1 +1 a pfet current limit duty cycle = 100%, current pulse width < 1ms 1.2 1.6 2.1 a oscillator frequency f osc 0.85 1.05 1.25 mhz thermal shutdown trip threshold 145 c en trip threshold ?40c t a +85c 0.3 0.96 1.5 v en input current v en = 0v to 6v ?1 +1 a notes: 4) 100% production test at +25c. specifications over the temperature range are guaranteed by design and characterization. c 6 yw top view en gnd sw 1 2 3 5 4 fb in mp1557_pd01_tsot23-5
mp2105 ? 1mhz 800ma synchronous step-down converter mp2105 rev. 1.2 www.monolithicpower.com 3 8/19/2005 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2005 mps. all rights reserved. tm typcial performanc e characteristics v in = 3.3v, v out = 1.8v, l1 = 4.7h, c1 = 4.7f, c3 = 10f, t a = +25 c, unless otherwise noted. mp2105-tpc03 load transient (i out =0ma to 500ma step) light load operation (i out =0ma) 0.603 0.602 0.601 0.600 0.599 0.598 0.597 feedback voltage (v) -40 +20 0 -20 +40 +60 +80 +100 -40 +20 0 -20 +40 +60 +80 +100 temperature ( c) mp2105-tpc01 feedback voltage vs temperature v in =3.3v v in =4.2v 100 95 90 85 80 75 70 65 60 55 50 efficiency ( % ) 10 100 1000 load current (ma) mp2105-ec01 95 90 85 80 75 70 65 60 55 50 efficiency ( % ) 10 100 1000 load current (ma) mp2105-tpc04 1.10 1.08 1.06 1.04 1.02 1.00 0.98 0.96 0.94 switching frequency (mhz) temperature ( c) mp2105-tpc02 switching frequency vs temperature mp2105-ec02 v in =3.3v v in =4.2v v out 100mv/div. i out 0.5a/div. v out 10mv/div. i l 0.2a/div. sw 2v/div.
mp2105 ? 1mhz 800ma synchronous step-down converter mp2105 rev. 1.2 www.monolithicpower.com 4 8/19/2005 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2005 mps. all rights reserved. tm typcial performanc e characteristics (continued) v in = 3.3v, v out = 1.8v, l1 = 4.7h, c1 = 4.7f, c3 = 10f, t a = +25 c, unless otherwise noted. mp2105-tpc09 short circuit protection (no load) mp2105-tpc07 heavy load operation i out = 800ma mp2105-tpc10 short circuit recovery (no load) mp2105-tpc08 startup from shutdown v out 10mv/div. i l 0.2a/div. i l =0 sw 2v/div. 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. pin functions pin # name description en 1 regulator enable control input. drive en above 1.5v to turn on the mp2105. drive en below 0.3v to turn it off (shutdown current < 0.1a). gnd 2 ground sw 3 power switch output. inductor connection to drains of the internal pfet and nfet switches. in 4 supply input. bypass to gnd with a 2.2f or greater ceramic capacitor. fb 5 feedback input. connect fb to the center point of the external resistor divider. the feedback threshold voltage is 0.6v.
mp2105 ? 1mhz 800ma synchronous step-down converter mp2105 rev. 1.2 www.monolithicpower.com 5 8/19/2005 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2005 mps. all rights reserved. tm operation the mp2105 is a constant frequency current mode pwm step-down converter. the mp2105 is optimized for low voltage, li-ion battery powered applications where high efficiency and small size are critical. the mp2105 uses an external resistor divider to set the output voltage from 0.6v to 6v. the device integrates both a main switch and a synchronous rectifier, which provides high efficiency and eliminates an external schottky diode. the mp2105 can achieve 100% duty cycle. the duty cycle d of a 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, and f osc is the oscillator frequency (1mhz). in en fb gnd sw + + -- 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) mp2105_bd01 figure 1?functional block diagram
mp2105 ? 1mhz 800ma synchronous step-down converter mp2105 rev. 1.2 www.monolithicpower.com 6 8/19/2005 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2005 mps. all rights reserved. tm 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. the mp2105 switches at a constant frequency (1mhz) 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 either the next cycle starts. dropout operation the mp2105 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 mp2105 has short circuit protection. when the 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 mp2105 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 oscill ations 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 (see figure 3). the feedback resistor r1 also sets the feedback loop bandwidth with the internal compensation capacitor (see figure 1). choose r1 around 500k ? 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 499k ? (1%) 499k ? (1%) 1.5v 499k ? (1%) 332k ? (1%) 1.8v 499k ? (1%) 249k ? (1%) 2.5v 499k ? (1%) 158k ? (1%) inductor selection a 1h to 10h 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.
mp2105 ? 1mhz 800ma synchronous step-down converter mp2105 rev. 1.2 www.monolithicpower.com 7 8/19/2005 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2005 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 d01605t-472 4.7 0.150 1.20 5.4x4.2x1.8 toko d52lc 4.7 0.087 1.14 5x5x2 sumida cr43-4r7 4.7 0.109 1.15 4.3x4.8x3.5 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 4.7f 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 pc board layout the high current paths (gnd, in and sw) should be placed very close to the device with short, direct and wide traces. input capacitor c1 needs to be as close as possible to the in and gnd pins. the external feedback resistors shall be placed next to the fb pin. keep the switching node sw short and away from the feedback network. figure 2 illustrates an example of pcb layout and signal routing. figure 2?mp2105 suggested layout
mp2105 ? 1mhz 800ma synchronous step-down converter notice: the information in this document is subject to change wi thout notice. please contact mps for current specifications. users should warrant and guarantee that third party intellect ual property rights are not infr inged upon when integrating mps products into any application. mps will not assume any legal responsibility for any said applications. mp2105 rev. 1.2 www.monolithicpower.com 8 8/19/2005 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2005 mps. all rights reserved. tm package information tsot23-5 gauge plane 0.25 bsc. 0.10 - + 0.400 0 0 4 (2 plcs) 10typ. 2.90 bsc (5 plcs) 0.300(min) l c typ . 0.950 l c typ . 0.950 2.80 bsc 1.60 bsc 3 3 0.500(max) seating plane 0.870.03 0.00-0.10 1.00 max. 0.127 typ. (2 plcs) 10 typ.
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