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PS0021 hi g h efficiency pfm step-up dc / dc converter description features ? pfm control asynchronous booster the PS0021 compact, high-efficiency, step-up dc- dc converters are available in tiny, 3-pin thin sot23 and 6-pin thin sot26 packages. they feature an extremely low 5a quiescent supply current to ensure the highest possible light-load efficiency. optimized for operation from one to two alkaline or nickel-metal-hydride (nimh) cells, or a single li+ cell, these devices are ideal for applications where extremely low quiescent current and ultra-small size are critical. ? up to 90% efficiency ? quiescent supply current: 5a ? zero shutdown current ? output voltage accuracy: 1% ? fixed output voltage ? provides 20ma from single aaa cell ? input voltage range: 0.8v to 5.5v ? startup voltage : 0.9v ? 3l sot-23 and 6l sot-26 package applications the PS0021 also feature proprietary noise- reduction circuitry, which suppresses electromagnetic interference (emi) caused by the inductor in many step-up applications. the family offers different combinat ions of fixed outputs, shutdown, and emi reduction (see selector guide). ? wireless mice, keyboard ? pagers ? remote controls ? wireless headsets ? wireless transmitters ? personal medical devices ? digital still cameras its unique design is optimized for high efficiency at light load condition. ? mp3/mp4 players ? single-cell battery-powered devices ? low-power hand-held instruments typical application circuit july 2007 www.picsemi.com ? 2007 power ic. all rights reserved. 1
PS0021 pin configuration pin designator name pin type function sw 1 switch connect induct or between sw and battery. july 2007 www.picsemi.com ? 2007 power ic. all rights reserved. 2 lbi 2 low?battery detector input. connect a resistive divider from battery to lbi to ground. en 3 enable en=high: normal operation. (supports both ttl and cmos logic). lbo 4 low battery detector output open?drain output. low?battery detector output is low when vlbi is less than 0.6 v. gnd 5 ground power ground vout 6 ic power supply vout supplie s power to step-up converter. note 1: limits are 100% production tested at ta = +25c. limits over the operating temperature range are guaranteed by design. note 2: guaranteed with the addition of a schottky mbr0520l external diode between lx and out when using the PS0021 with only one cell, and assumes a 0.3v voltage drop across the schottky diode (see figure 3). note 3: supply current is measured with an ammeter between the outp ut and out pin. this current correlates directly with actual battery supply current, but is reduced in value according to the step-up ratio and efficiency. note 4: vout forced to the following conditio ns to inhibit switching: vout = 1.05 ? vout (nom) vout = 3.465v
p s00 21 block diagram absolute maximum ratings out, shdn, batt, sw to gnd ???????????????????????????..................... -0.3v to +6v fb to gnd ???????????????????????????????????????.. -0.3v to (vout + 0.3v) out, sw current ?????????????????????........................................................................1a continuous power diss ipation (ta = +70c) 6-pin thin sot26 (derate 7.1mw/c abov e +70c) ?????????????? ???????.???.....571mw operating temperature range ???????????????????????.............................-40c to +85c junction temperature ??????????????? ???????....... .................................................+150c storage temperature range ??????????????????????.................................-65c to +150c lead temperature (soldering, 10s) ???????????????????????????????????. +300c july 2007 www.picsemi.com ? 2007 power ic. all rights reserved. 3
PS0021 electrical characteristics july 2007 www.picsemi.com ? 2007 power ic. all rights reserved. 4 ( v batt = 1.2v, v out = 3.3v, v out = v out (nom) , shdn = out, rl = , t a = 0c to +85c , unless otherwise noted. typical values are at t = +25c.) a unit parameter symbol conditions min typ max operating input voltage v ( note 2 ) 5.5 v in output voltage variation v 3.2 3.3 3.4 v out minimum startup input voltage rl= 30k? 0.9 v hold on voltage 1 ma load 0.7 v switch leakage 5 na n-channel measured from sw pin voltage and 1.4 ? r ds(on) on-resistance inductor current during sw on time maximum oscillating freq v forced = v (nom) * 0.95 80 100 120 khz out out f osc duty ratio d v forced = v (nom) * 0.95 65 75 85 % max out out efficiency eff 85 % 5 a quiescent current into out v = v in out +0.5v measurement of the ic input current(v pin) (notes 3, 4) out (no switching) quiescent current into out v forced = v (nom) * 0.95 25 a out out shutdown current into out (notes 4) en= 0v 1 a 1.2 v il shdn voltage threshold v ih 0.4 mv shdn input bias v = 5.5v 1.1 na shdn current low battery detector lbi voltage threshold v forced = v (nom)*1.05 665 670 675 mv out out lbi input hysteresis v forced = v (nom)*1.05 15 18 22 mv out out lbi input current v forced = v (nom)*1.05 0.02 na out out lbo output low voltage force 20ma into lbo 0.45 0.50 0.6 v lbo output leakage current lbo= 6.0v 0.1 a
PS0021 typical operating characteristics (all specifications are at t =+25c, v = 1.5v, circuit of typical application circuit, unless otherwise specified.) a in july 2007 www.picsemi.com ? 2007 power ic. all rights reserved. 5
PS0021 typical operating characteristics (continued) july 2007 www.picsemi.com ? 2007 power ic. all rights reserved. 6
PS0021 typical operating characteristics (continued) july 2007 www.picsemi.com ? 2007 power ic. all rights reserved. 7
PS0021 typical operating characteristics (continued) july 2007 www.picsemi.com ? 2007 power ic. all rights reserved. 8
PS0021 operation thermal overload protection the PS0021 is a compact, high-efficiency, synchronous boost converter in a sot-26 package designed for space- restricted applications. the part is available with adjustable output voltages ranging from 2.5v to 5.0v. it is able to start up with input voltages as low as 0.8v and operate with input voltages down to 0.5v. with its internal synchronous rectifier and low on-resistance of the internal nmos switch, the device maintains high efficiency over a wide range of load current. as shown in the block diagram, the PS0021 consists of accurate band gap core, error amplifier, start-up oscillator and control logic unit along with pmos and nmos switches. with current mode pwm control, th e PS0021 has ultra-fast line and improved load regulation. moreover, the PS0021 provides real shutdown circuitry which disconnects the output from the input during shutdown and results in the discharge of the output to ground. thermal overload protection limits the total power dissipation in the PS0021. when the junction temperature exceeds t j = +145 c, the thermal sensor signals the shutdown logic and turns off most of the internal circuitry. the thermal sensor turns the internal circuitry on again after the ic?s junction temperature drops by 15 c. thermal overload protection is designed to protect the PS0021 in the event of a fault condition. fo r continuous operation, do not exceed th e absolute maximum junction temperature rating of t j = +125 c. current limit protection the PS0021 includes a current limiter that monitors the peak inductor current through the nmos switch and turns the nmos switch off when the inductor peak current exceeds 150ma. start-up mode the PS0021 starts up typically at 0.8v. when it is turned on, the device gets its start up bias from vin. a start-up oscillator, which runs typically at 650 khz, takes the output voltage high enough so that v light load operation exceeds v july 2007 www.picsemi.com ? 2007 power ic. all rights reserved. 9 out in . once v the PS0021 provides improved light load efficiency. the internal zero current comparator monitors the inductor current to the load and shuts off the pmos switch once this current reduces to some low value (typically 50ma). this prevents the inductor current from reversing its polarity, avoiding back-charg ing and thus improving the efficiency at light loads. at that time, both the nmos and pmos switches remain off. however, normal operation starts again when the output voltage falls below the regulation point. the ic automa tically skips pulses at light load, thus providing better efficiency. exceeds v out in , the internal bias switches from v to v in out by an internal bias-select circuit. thus, once started (i.e. v out exceeds v in ), the internal circuit bias is completely independent of v in . the start-up oscillator runs at 66% duty cycle at around 650khz. once v out exceeds v in (typically 1.9v), the start-up oscillator is disabled and the normal fixed t on pwm operation takes over. internal pmos and nmos switches the PS0021 features a 0.45 nmos switch and a 0.6 pmos switch. in normal operation, these switches are alternatively turned on and t hus initiate the charging of the inductor from vin and then discharging of it to the output capacitor and the load. however, between the event of one switch turning off and the other turning on, a dead time is provided to avoid a huge in-rush current from the output to ground via switches. during the dead time, both switches remain off and the inductor discharges via the body diode of the pmos switch to the output.
PS0021 enable input under voltage lockout the PS0021 features an active-high cmos input enable pin (shutb) that allows on/o ff control of the regulator. when shutb=low, shutdown of the chip occurs and at that time almost no quiescent current (<1a) flows. the output capacitor can be completely discharged through the load or the feedback resistors for real output shut- down. a discharge switch is internally connected between vin and sw. the enable (shutb) input is ttl/cmos compatible. connect shutb to vin for normal operation. when the supply becomes too low (typically below 1.8v), the PS0021 produces an internal uvlo (under voltage lockout) signal that disabl es the normal pwm operation and enables the start-up oscillator to run at a fixed frequency. at this stage, very few circuits are operational. when the oscillator raises th e supply to above 1.9v, the uvlo signal is disabled an d the normal pwm mode takes over the operation of the start-up oscillator. this mechanism protects the chip from producing false logic due to low input supply. track mode in track mode vout follows vin. difference between vout and vin is determined by the load current and the schottky forward voltage drop at that current. july 2007 www.picsemi.com ? 2007 power ic. all rights reserved. 10
PS0021 package information july 2007 www.picsemi.com ? 2007 power ic. all rights reserved. 11
PS0021 disclaimers life support power ic?s products are not designed to be used as co mponents in devices intended to support or sustain human life. the use of power ic?s products in components in tended for surgical implants into the body or other applications, in which failure of power ic?s products co uld create a situation where personal death or injury may occur, is not authorized without the express wri tten approval of power ic?s chief executive officer. power ic will not be held liable for any damages or claims resulting from the use of its products in medical applications. military power ic?s products are not designed for use in milit ary applications. the use of power ic?s products in military applications is not authorized without the ex press written approval of power ic?s chief executive officer. power ic will not be held liable for any damages or claims resulting from the use of its products in military applications. right to make changes power ic reserves the right to change this document and/or this product without notice. customers are advised to consult their power ic sale s representative before ordering. july 2007 www.picsemi.com ? 2007 power ic. all rights reserved. 12

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