unisonic technologies co., ltd l1923 preliminary cmos ic www.unisonic.com.tw 1 of 7 copyright ? 2011 unisonic technologies co., ltd qw-r502-440.c 500ma high psrr ldo regulators ? description the utc l1923 is a low supply current, low dropout linear regulator. it is operating at 2.5v - 5.5v. t he supply current is as low as 55 a in the no?load condition. in the shut down mode, the maximum supply current is less than 1 a. a built-in over-temperature protecti on circuit is designed to protect the device from being damaged by ther mal overload. the over-current protection limit is set at 800ma (typ.) the utc l1923 can be operated on the following two modes. when the set pin is connected to ground, the output of l1923 is a pre-set value and the external components are not needed to decide the output voltage. when an output other than the preset value is needed, two external resistors should be used as voltage dividers and then the output voltage is decided by the resistor ratio. the utc l1923 is generally used in notebook computers, cellular phones, pdas, digital still camera and video recorders and other hand-held devices. ? features * low no-load supply current: 90a * guaranteed 500ma output current * dropout voltage is 200mv @ 250ma load *otp(over-temperature protection) and short-circuit protection * two modes of operation: fixed mode 3.3v,3.5v,3.9v adjustable mode: 1.25v - 5.5v * maximum supply current in shutdown mode is less than 1a * low output noise at 238vrms * stability with lost cost ceramic capacitors ? ordering information ordering number package packing lead free halogen free l1923l-xx-af5-r l1923g-xx-af5-r sot-25 tape reel note: xx: output voltage, refer to marki ng information.
l1923 preliminary cmos ic unisonic technologies co., ltd 2 of 7 www.unisonic.com.tw qw-r502-440.c ? marking information package voltage code marking sot-25 33:3.3v 35:3.5v 39:3.9v 4 5 3 2 1 bq g voltage code g: halogen free l: lead free ? pin configuration 1 shdn 2 gnd 3 in 4 out 5 set ? pin description pin no. pin name description 1 shdn active-low shutdown input. a logic low redu ces the supply current to less than 1a. connect to in for normal operation. 2 gnd ground. this pin also functions as a heatsink. solder to large pads or the circuit board ground plane to maximize thermal dissipation. 3 in regulator input. supply voltage can range from +2.5v to +5.5v. bypass with 1f to gnd 4 out regulator output. fixed or adjustable from 1.25v to +5.5v. sources up to 500ma. bypass with a 4.7f, 0.2 ? typical esr capacitor to gnd. 5 set feedback input for setting the output volt age. connect to gnd to set the output voltage to the preset output voltage. connect to an external resistor divider for adjustable-output operation.
l1923 preliminary cmos ic unisonic technologies co., ltd 3 of 7 www.unisonic.com.tw qw-r502-440.c ? block diagram
l1923 preliminary cmos ic unisonic technologies co., ltd 4 of 7 www.unisonic.com.tw qw-r502-440.c ? absolute maximum rating parameter symbol ratings unit v in to gnd -0.3~7 v output short-circuit du ration infinite set to gnd -0.3~7 v shdn to gnd -0.3~7 v shdn to in -7~0.3 v out to gnd -0.3~(v in +0.3) v power dissipation (t a =25c) p d 520 mw junction temperature t j 150 c operating temperature t opr -40~85 c storage temperature t stg -65~160 c notes: absolute maximum ratings are those values beyond which the device could be permanently damaged. absolute maximum ratings are stress ratings only and functional device oper ation is not implied. ? thermal data parameter symbol ratings unit junction to ambient ja 240 c/w ? electrical characteristics (v in =+3.6v, v shdn =v in , t a =t j =+25c, unless otherwise specified.) (note 1) parameter symbol test conditions min typ max unit input voltage (note 2) v in 2.5 5.5 v output voltage accuracy v out variation from specified v out , i out =1ma -2 2 % adjustable output voltage v out (note 3) v set 5.5 v maximum output current 500 ma current limit (note 4) i limit 600 800 ma short circuit current isc 120 ma ground pin current i q 90 120 a dropout voltage (note 5) v drop i out =250ma 200 mv i out =500ma 400 500 line regulation v lnr set=gnd, v in =v (std) +0.1v~5.5v, i out =10ma 0.06 0.12 %/v load regulation v ldr i out = 10ma ~500ma 0.02 0.1 %/ma ripple rejection psrr f=100hz, 0.45v p-p , i out =10ma 65 db output noise noise f 100khz, i out =0a 136 v (rms) f 100khz, i out =250ma 238 f 100khz, i out =500ma 253 shutdown shdn input threshold v ih regulator enabled 1.5 v v il regulator shutdown 0.4 shdn input bias current i shdn v shdn = v in t a = +25c 0.003 0.1 a shutdown supply current i qshdn v out = 0v t a = +25c 0.2 1 a set input set reference voltage (note 3) v set v in = 2.5v ~ 5.5v, i out = 1ma t a = +25c 1.225 1.25 1.275 v t a = t min to t max 1.25 set input leakage current i set v set = 1.3v (note 3) t a = +25c 5 30 na thermal protection thermal shutdown temperature t shdn 145 c thermal shutdown hysteresis t shdn 25 c notes: 1.limits is 100% production tested at t a = +25c. low duty pulse techniques are used during test to maintain j unction temperature as close to ambient as possible. 2.guaranteed by line regulation test. 3. a djustable mode only. 4.not tested. for design purposes, the current limit should be considered 600ma minimum to 800ma maximum. 5.the dropout voltage is defined as (v in -v out ) when v out is 100mv below the target value of v out .
l1923 preliminary cmos ic unisonic technologies co., ltd 5 of 7 www.unisonic.com.tw qw-r502-440.c ? application information the utc l1923 contains an error amplifier, 1.25v bandgap refere nce, pmos output transistor, internal feedback voltage divider, mode comparator, shutdo wn logic, over current protection ci rcuit, and over temperature protection circuit as shown in the block diagram. the process of operation is like this: t he mode comparator compares the voltag e of set pin with a pre-set voltage reference of 0.35v. if the voltage of set pin is smaller than 0.35v, the internal feedback voltage divider?s central tap is connected to the error amplifier?s non-inverting input. th en, the error amplifier compar es non-inverting input with the 1.25v bandgap voltage reference. if the feedback voltage is larger than th e voltage reference 1.25v, the error amplifier?s output becomes higher. this makes the pmos output transistor?s v gs (gate-to-source voltage) smaller, in that condition, the current carrying capab ility of the pmos output trans istor is reduced, as a re sult the output voltage decreases until the feedback voltage becomes equal to 1.25v. similarly, when the feedback voltage is less than 1.25v, the error amplifier causes the output pmos to conductor more curr ent to pull the feedback voltage up to 1.25v. thus, through this feedback action, the error amp lifier, output pmos, and the vo ltage dividers effectively form a unity-gain amplifier with the feedback voltage force to be the same as the 1.25v bandgap reference. the output voltage, v out , can be calculated as follows: v out = 1.25 (1 + r1/r2). (1) alternatively, the relationship between r1 and r2 is expressed in the following: r1 = r2 (v out /1.25 - 1). (2) in order to reduce power dissipation and loop stability, it is recommended that r2 is 100k ? . for utc l1923-330 , r1 is 164k, and the pre-set v out is 3.30v. in figure 2, the set pin voltage will be larger than 350mv when external voltag e divider functions in the operation. the non-inverting input of the amplifier will be connected to the external voltage divider. the conditions of equations 1 and 2 are still true since the operati on of the feedback loop is the same. equation 1 still pr esents the output voltage. over current protection to monitor the output current, the utc l1923 applies a current mirror. a portion of the pmos output transistor?s current is mirrored to a resistor such that the voltage across this resistor is proportional to the output current. once the output current exceeds limit threshold, utc l1923 would be protected with a limit ed output current. further more, when the output is short to ground, the outpu t current would be folded-back to a less limit. over temperature protection over-temperature protection circuit is designed to pr event this device from being damaged due to abnormal temperature during operation. it is used to turn off the out put mosfet if the temperatur e is higher than 145c, the switch does not turn on until t he temperature drops to 120c.
l1923 preliminary cmos ic unisonic technologies co., ltd 6 of 7 www.unisonic.com.tw qw-r502-440.c ? application information (cont.) shutdown mode the utc l1923 enters shutdown mode if the shdn pin is applied to a logic low voltage. under the shutdown state, all the analog circuits are turned off completely , which reduces the current c onsumption to only the leakage current . the utc l1923 output pass transistor would get into high impedance level. there is an internal discharge path to help to shorten discharge delay time. operating region and power dissipation the utc l1923 is a linear regulator, so the power dissipation can be expressed by: p = i out (v in ? v out ). and the maximum power dissipation is calculated by: p d(max) = (t j ?t a )/ ja ,=(150c -25c)/240c/w= 520mw (where (t j ?t a ) is the temperature difference the die and the ambient air; ja , is the thermal resistance of the chosen package to the ambient air.) for surface mount device, heat sinki ng is accomplished by using the heat spreading capabilities of the pc board and its copper traces. the die attachment area of the utc l1923 ?s lead frame is connected to pin 2, which is the gnd pin. therefore, the gnd pin of utc l1923 can carry away the heat of the utc l1923 die very effectively. connecting the gnd pin to ground using a large gr ound plane near the gnd pi n can improve the power consumption. capacitor selection and regulator stability a 1f capacitor on the input and a 4.7f capacitor on the output are recommended for mo st applications of the u tc l1923 . to get a better supply-noise rejection and transient response, input capacitors with larger values and lower esr are needed. a higher-value input capacitor ( 10f) may be necessary if large, fast transients are anticipated and the device is located se veral inches from the power source. power-supply rejection and operation from sources other than batteries the utc l1923 is particularly designed to deliver low dropout voltages and low quiescent currents in battery- powered systems. power-supply rejection is 42db at low frequencies. as the frequenc y increases above 20khz, the output capacitor is the major contributor to the rejection of power-supply noise. when operating from sources other than batteries, improv e supply-noise rejection and transient response by increasing the values of the input and output capacitors, and usi ng passive filtering techniques. input-output (dropout) voltage the minimum input-output voltage differential (or dropout vo ltage) of a regulator dete rmines the lowest usable supply voltage. in battery-powered system applications, this will determine the useful end-of-life battery voltage. because the utc l1923 use a p-channel mosfet pass transistor, t heir dropout voltage is a function of r ds(on) multiplied by the load current.
l1923 preliminary cmos ic unisonic technologies co., ltd 7 of 7 www.unisonic.com.tw qw-r502-440.c ? typical application circuit shdn gnd set utc l1923 out + c in 1 - c out 4.7 output battery fixed mode in shdn gnd utc l1923 out + c in 1 - c out 4.7 output battery adjustable mode set r1 r2 in utc assumes no responsibility for equipment failures that result from using products at values that exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or other parameters) listed in products specifications of any and all utc products described or contained herein. utc products are not designed for use in life support appliances, devices or systems where malfunction of these products can be reasonably expected to result in personal injury. reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. the information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice.
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