PT1202 1.9mh z, 600 ma synchronous step - do wn dc - dc converter china reso urces powtech (shanghai) co., ltd. www.crpowtech.com page . 1 PT1202_ds _ rev en 3.3 general description the PT1202 is a high efficiency monolithic current mode synchronous buck regulator with a constant operation frequency. a main switch and a synchronous switch are integrated in PT1202, the device has high efficiency and no external scho ttky diode needed. supply current is 300ua during operation and drops to 1a in shutdown. the 2.5v to 5.5v input voltage range makes the PT1202 ideally suited for single li - ion battery - powered applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems. automatic skip cycle operatio n mode at light loads provides very low output ripple for noise sensitive applications. internal 1. 9 mhz switching frequency allowing the use of small surface mount inductors and capacitors. ultra low output voltages are easily available with the 0.6v feedb ack reference voltage. the PT1202 is offered in a low profile sot package and is available in an adjustable version and fixed output voltages versions from 0.6v to 1.8v. f eatures ? high efficiency: up to 96% ? low quiescent current: 30 0a ? 600 ma output current ? 2.5v to 5.5v input voltage range ? 1. 9 mhz constant frequency operation ? internal integrated main switch and rectifier, n o schottky diode required ? low dropout operation: 100% duty cycle ? 0.6v reference allows low output voltages ? shutdown mode draws1a supply current ? current mode operation for excellent line and load transient response ? over - temperature protected ? low profile sot packag e ? rohs compliant a pplications ? cellular and smart phones ? personal information appliances ? micropr ocessors and dsp core supplies ? wireless and dsl modems ? digital still cameras ? mp3 players and pdas ? portable instruments ordering information p ackage t emperature r ange ordering part number t ransport m edia m arking sot23 - 5 - 40 o c to 85 o c PT1202e23e - adj tape and reel 3000 units 1202z typical application circuit v i n r u n g n d o u t / f b s w 1 2 4 3 p t 1 2 0 2 5 c i n 4 . 7 u f c e r 2 . 2 u h v o u t c o u t 1 0 u f c e r v i n 2 . 7 ~ 5 . 5 v v i n r u n g n d o u t / f b s w 1 2 0 2
PT1202 1.9mh z, 600 ma synchronous step - do wn dc - dc converter china reso urces powtech (shanghai) co., ltd. www.crpowtech.com page . 2 PT1202_ds _ rev en 3.3 pin assignment pin descriptions pin names pin no. description run 1 chip enable, active with h gnd 2 chip ground sw 3 output of int ernal switches vin 4 power supply v fb /v out 5 regulated feedback/output voltage absoloute maximum rating (note1) symbol items value unit v in i nput supply voltage C 0.3 to 6 v v run run pin voltage C 0.3 to vin v v fb fb pin voltage C 0.3 to vin v v sw s w pin voltage C 0.3 to (vin + 0.3 ) v i sw sw pin source/sink current (dc) 1 a i sw sw pin source/sink current (peak) 1.5 a t j junction temperature 125 c t oper operating temperature range C 40 to 85 c t stg storage temperature range C 65 to 150 c t s older lead temperature (soldering, 10 sec) 300 c ja thermal resister 220 c /w note1: absolute maximum rating s are those value s beyond which the life of the device maybe impaired. t o p v i e w 1 2 0 2 r u n 1 g n d 2 s w 3 4 v i n 5 v f b / v o u t s 5 p a c k a g e 5 - l e a d p l a s t i c s o t - 2 3
PT1202 1.9mh z, 600 ma synchronous step - do wn dc - dc converter china reso urces powtech (shanghai) co., ltd. www.crpowtech.com page . 3 PT1202_ds _ rev en 3.3 electrical characteristics ta = 25c. vrun=vin = 3.6v unless otherwis e specified . symbol parameter conditions min typ max units v fb regulated feedback voltage t a =25 0.588 0.6 00 0.612 v ? v fb line regulation v in = 2.5v to 5.5v 0.04 0. 5 %/v i fb vfb input bias current 0 30 na i pk peak inductor current v in = 3v, v fb = 0.5v, duty cycle < 35% 1 a v loadreg load regulation 0.5 % v in input voltage range 2.5 5.5 v i s input dc bias current active mode shutdown v fb = 0. 5 v or v out = 90 %, i load = 0a v run = 0v, vin = 4.2v 300 0.1 400 1 a f osc oscillator frequ ency v fb = 0.6v or vout = 100% 1. 5 1.9 2. 3 mhz r pfet rds(on) of p - channel fet i sw = 100ma 0.4 0.5 ? r nfet rds(on) of n - channel fet i sw = C 100ma 0.35 0.45 ? i lsw sw leakage v run = 0v, v sw = 0v or 5v, v in = 5v 0.01 1 a v run run threshold voltage - 40 t a 85 0.3 1.0 1.50 v note: the min and max value is guaranteed by final test or lab stati stic.
PT1202 1.9mh z, 600 ma synchronous step - do wn dc - dc converter china reso urces powtech (shanghai) co., ltd. www.crpowtech.com page . 4 PT1202_ds _ rev en 3.3 simplified block diagram operation description the PT1202 is a high efficiency monolithic current mode synchronous buck regulator with a constant operation frequency. its internal integrated mosfets achieve high efficiency. ultra low output volta ges are easily available with the 0.6v feedback reference voltage. internal fixed 1. 9 mhz switching frequency allowing the use of small surface mount inductors and capacitors. the 2.5v to 5.5v input voltage range and 600 ma output current make the PT1202 ide ally suited for single li - ion battery - powered applications. current mode pwm control loop slope compensated current mode pwm control and cycle - by - cycle current limit provides stable operation and excellent line and load regulation. during normal operation, the internal top power mosfet is turned on each cycle when the rising edge of the oscillator sets the rs latch, and turned off when rising edge of the pwm comparator resets the rs latch. while the top mosfet is off, the bottom mosfet is turned on until ei ther the inductor current starts to reverse or the beginning of the next clock cycle. the ovdet comparator controls output transient overshoots is smaller than 8% by turning the main mosfet off until the fault is removed. skip - cycles mode operation at lig ht loads, the PT1202 enters skip - cycle mode automatically. in this mode, the inductor current may reach zero or reverse on each cycle . the pwm control loop will automatically skip cycles to maintain output regulation. the bottom mosfet is turned off by the current reversal comparator, ir - cmp arator , and the switch voltage will ring. this is discontinuous mode operation, and is normal behavior for the switching regulator. current fold - back operation t he frequency of the oscillator is reduced to about 210 k hz w hen the output voltage is smaller than 50% of normal value ; which ensures the inductor current has more time to decay, thereby preventing runaway. the oscillators frequency will progressively increase to 1. 9 mhz when the output voltage rises above 50%. low - dropout operation when the input voltage deceases to the value of output voltage, the control loop remains the main mosfet on until it reaches 100% duty cycle. the output voltage then is the input voltage minus the voltage drop across the main switch a nd the inductor. caution must be exercised to ensure the heat dissipated not to exceed the maximum junction temperature of the ic because the rdson of the main mosfet increases and the efficiency of the converter decrease . maximum load current the PT1202 o perates with input voltage as low as 2.5v. however, the maximum load current decreases when the input voltage deceases because of the large ir drop of the main switch and the synchronous switch. and the slope compensation reduces the peak inductor current.
PT1202 1.9mh z, 600 ma synchronous step - do wn dc - dc converter china reso urces powtech (shanghai) co., ltd. www.crpowtech.com page . 5 PT1202_ds _ rev en 3.3 typical performance characteristics (from figure 1, ta=25 unless otherwise specified) efficiency vs. input voltage efficiency vs. output current efficiency vs. output current efficiency vs. output current reference voltage (v) vs. temperature ( ) oscillator frequency vs. vin 0.5 1 10 100 700 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 vin=4.2v vin=2.7v vin=3.6v vout=1.2v efficiency vs output current (ma) efficiency output current (ma) vin=2.7v vin=3.6v vin=4.2v 0.5 1 10 100 600 0.50 0.00 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 vin=4.2v vin=3.6v vin=2.7v efficiency vs output current (ma) output current (ma) efficiency vout=1.5v vin=2.7v vin=3.6v vin=4.2v 0.5 1 10 100 600 0.45 0.00 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 vin=4.2v vin=3.6v vin=2.7v vout=2.5v efficiency efficiency vs output current (ma) output current (ma) vin=2.7v vin=3.6v vin=4.2v
PT1202 1.9mh z, 600 ma synchronous step - do wn dc - dc converter china reso urces powtech (shanghai) co., ltd. www.crpowtech.com page . 6 PT1202_ds _ rev en 3.3 oscillator frequency vs. temperature ( ) supply current vs. temperature ( ) supply current vs. supply voltage start - up from shutdown load step load step
PT1202 1.9mh z, 600 ma synchronous step - do wn dc - dc converter china reso urces powtech (shanghai) co., ltd. www.crpowtech.com page . 7 PT1202_ds _ rev en 3.3 applicati ons information figure 1 figure 2 setting the output voltage figure 1 shows the application of fixed output voltage version of PT1202. there are 0.6v to 5v versions are available. in these vers ions, the output voltage is set by an internal resister divider. figure 2 shows the application of adjust version of PT1202. in this version, the output voltage is set by an external resister divider according to the following formula: inductor selection for most applications, the PT1202 operates well with inductors of 1 uh to 4.7 uh . low inductance values are physically smaller but require fast switching, which results in efficiency loss. the inductor value can be calculated from foll owing equation: table 1 list some typical surface mount inductors that adapt to PT1202 applications. input and output capacitor selection the input capacitor reduces the surge current drawn from the input and switching noise from the device. to prevent large voltage transients, a low esr input capacitor sized for the maximum rms current must be used. the maximum rms capacitor current is given by: ceramic capacitor with x5r or c7r dielectrics are highly reco mmended because of their low esr and small temperature coefficients . a 4.7uf ceramic capacitor for most applications is sufficient. the output capacitor is required to obtain small output voltage ripple and ensure regulation loop stability. typically, once the esr requirement for cout has been met, the rms current generally far exceeds the ripple current requirement . the output ripple v out is determined by: where f is the operating frequency, cout is the output capacitor and i l is the ripple current of inductor current. ceramic capacitors with x5r or c7r dielectrics are recommended due to their low esr and high current rating. a 10uf ceramic capacitor for most applications is recommended for low output voltage ripple and good loop s tability. adapter/usb applications for usb or adapter application s , there is 10% voltage variation in the power supply; this device c ould be harmed if v in is higher than 5.5v. to protect the device, a zener diode with 5.6v break down voltage d1 in fig. 3 is suggested to be added between v in and gnd in table 1. typical surface mount inductors v i n r u n g n d o u t / f b s w 1 2 4 3 p t 1 2 0 2 5 c i n 4 . 7 u f c e r 2 . 2 u h v o u t c o u t 1 0 u f c e r v i n 2 . 7 ~ 5 . 5 v v i n r u n g n d o u t / f b s w 1 2 0 2 v i n r u n g n d o u t / f b s w 1 2 4 3 1 2 0 2 5 c i n 4 . 7 u f c e r c o u t 1 0 u f c e r r 2 r 1 v i n 2 . 7 ~ 5 . 5 v 2 . 2 u h v o u t c 1 ? ? ? ? ? ? ? ? ? 1 2 1 6 . 0 r r v v out osc l in out in out f i v v v v l ? ? ? ? ? ? ) ( ? ? in out in out omax rms v v v v i i 2 1 ) ( ? ? ? ) 8 1 ( out l out fc esr i v ? ? ? ? ?
PT1202 1.9mh z, 600 ma synchronous step - do wn dc - dc converter china reso urces powtech (shanghai) co., ltd. www.crpowtech.com page . 8 PT1202_ds _ rev en 3.3 t his kind of applications. layout guideline 1. the power traces, including the vin trace, the gnd trace, and the sw trace should be kept short, direct and wide. 2. the v fb pin should be connected directly to the feedback resistor, and kept away from the switching node, sw. the resistive divider r1/r2 must be connected between the (+) plane of cout and ground. 3. place the (+) plane of cin to the vin pin as close as possible. 4. keep the ( ) plates of cin and cout as close as possible. 5. a full gnd plane without gap break is good for system noise. v i n r u n g n d o u t / f b s w 1 2 4 3 1 2 0 2 5 d 1 5 . 6 v c i n 4 . 7 u f c e r c o u t 1 0 u f c e r r 2 r 1 v i n , 5 . 5 v 2 . 2 u h v o u t c 1 2 2 p f
PT1202 1.9mh z, 600 ma synchronous step - do wn dc - dc converter china reso urces powtech (shanghai) co., ltd. www.crpowtech.com page . 9 PT1202_ds _ rev en 3.3 package information 5ld sot23 - 5 package outline dimensions (all dimensions in mm)
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