3a, 18v, 350khz synchronous step-down converter china resources powtech (shanghai) limited www.crpowtech.com page1 PT1204_dsb rev en0.1 PT1204 general description the PT1204 is a monolithic pulse-width-modulated (pwm) synchronous step-down switch mode regulator with two internal power mosfets. it achieves 3a continuous output current over a wide input supply range with excellent load and line regulation. current mode operation provides fast transient response and eases loop stabilization. fault condition protection includes cycle-by-cycle current limit and thermal shutdown. the PT1204 requires a minimum number of external components, available in esop-8 package. features z 3a output current z 0.085 ? internal power mosfet switch z stable with low esr output ceramic capacitors z up to 93% efficiency z fixed 350khz frequency z thermal shutdown z cycle-by-cycle over current protection z wide 4.75v to 18v operating input range z output adjustable from 0.925v to 15v z available in esop8 packages application z pc monitors z lcd tv z distributed power systems z network systems z fpga, dsp, asic power supplies z notebook computers ordering information package temperature range ordering part number transport media marking esop-8 -40 to 85 PT1204eesh tape and reel 2500 units PT1204 xxxxxx note: typical application circuit xxxxxx assembly factory code lot number figure1 PT1204 typical application circuit
3a, 18v, 350khz synchronous step-down converter china resources powtech (shanghai) limited www.crpowtech.com page2 PT1204_dsb rev en0.1 PT1204 pin assignment bs in sw gnd ss en comp fb top view exposed pad on backside connect to gnd pin pin descriptions sop8 pin no. pin names description 1 bs high-side gate driver boost input. bs supplies the drive for the high-side n-channel mosfet switch. connect a 0.01uf or greater capacitor from sw to bs to power the high side switch. 2 in supply voltage. the PT1204 operates from a +4.75v to +18v unregulated input. c1 is needed to prevent large voltage spikes from appearing at the input. 3 sw power switching output. this pin is connected to in through m1 or to gnd through m2. 4 gnd ground 5 fb feedback input. fb senses the output voltage through an external resistive divider which is connected from the output to gnd. 6 comp compensation node. comp compensates the control loop by connecting a serial rc network to ground. in some cases, an additional capacitor from comp to gnd is required. 7 en enable input. en is digital input that turns the regulator on or off. drive en high to turn on the regulator, drive it low to turn it off. pull up to in with 100k ? resistor for automatic startup. 8 ss soft-start. connect a capacitor from ss to gnd to program the soft-start period. leave it open if unused. esop8
3a, 18v, 350khz synchronous step-down converter china resources powtech (shanghai) limited www.crpowtech.com page3 PT1204_dsb rev en0.1 PT1204 absolute maximum ratings (note 1) symbol items value unit in supply voltage -0.3~24 v sw switch node voltage -0.3~24 v bs bootstrap voltage vsw-0.3~vsw+6 v fb feedback voltage -0.3~6 v en enable/uvlo voltage -0.3~6 v comp comp voltage -0.3~6 v tstg storage temperature range -65~+150 recommended operating range symbol items value unit vin supply voltage 4.75~18 v topt operating temperature -40~+85 note 1: absolute maximum ratings indicate limits beyond which damage to the device may occur. recommended operating range indicates conditions for which the device is functional, but do not guarantee specific performance limits. electrical characteristics state dc and ac electrical specifications und er particular test conditions which guarantee specific performance limits. this assumes that the device is within the operatin g range. specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device performance. electrical characteristics the following specifications apply for v in =12v, v out =3.3v, load=0.5a, t a =25 o c, unless specified otherwise. symbol items conditions min. typ. max. unit iq supply current en=2v; vfb=1v 1.5 2.0 ma vfb feedback voltage 0.900 0.925 0.946 v av error amplifier voltage gain 400 v/v gea error amplifier trans-conductance ? icomp=+/-10ua 800 ua/v r_dson1 high side switch on resistance 0.085 ? r_dson2 low side switch on resistance 0.085 ? ipd shutdown supply current ven = 0v 13 20 ua i_leakage high side switch leakage current (2) ven=0v; vsw=0v 0 10 ua i_clh high side switch current limit (2) 3.8 5 a i_cll low side switch current limit (2) 1.0 a gcomp comp to current sense trans-conductance 5 a/v fosc1 oscillation frequency 350 khz
3a, 18v, 350khz synchronous step-down converter china resources powtech (shanghai) limited www.crpowtech.com page4 PT1204_dsb rev en0.1 PT1204 electrical character istics (continued) symbol items conditions min. typ. max. unit fosc2 short circuit oscillation frequency vfb=0.2v 90 khz dmax maximum duty cycle vfb=0.8v 90 % ven en threshold voltage 1.1 1.5 2.0 v ven_hyst en threshold voltage hysteresis 0.2 v tsd thermal shutdown 160 oc note 2: guaranteed by design. simplified block diagram q q set clr s r pwm comparator regulator oscilator 90k/350k + - 1.2v 6ua scp comparator current sense amplifier + - 5v 2 vin 4 gnd fb 5 ss 8 en 7 3 sw 1 bs 6 comp ovp comparator ovp + - + - thermal shutdown 0.3v 1.1v 0.925v 5v uvlo tsd ovp !en m1 0.085 ? m2 0.085 ? error comparator + - figure 2?functional block diagram
3a, 18v, 350khz synchronous step-down converter china resources powtech (shanghai) limited www.crpowtech.com page5 PT1204_dsb rev en0.1 PT1204 operation description the PT1204 is a synchronous rectified current mode step-down regulator. it regulates input voltage from 4.75v to 18v down to a voltage as low as 0.925v, and supplies up to 3a of load current. on the rising edge of internal oscillator, the low-side mosfet will be turned off and the high-side mosfet will be turned on if the pwm comparator output is low. the output voltage is measured at fb pin through a resistive voltage divider and amplified through the internal error amplifier, the voltage at the comp pin is compared with the switch current. as the switch current ramp up, the pwm comparator will output high, the high-side mosfet will be turned off and the low-side mosfet will be turned on until the next rising edge of the internal oscillator. when the output voltage exceeds 20% of the nominal regulated voltage, the over-voltage comparator will be tripped and turn off the high-side mosfet by discharging the ss pin to gnd. when the fb voltage is less than 0.3v, the frequency of the internal oscillator will be set to 90khz to decease the short circuit current.
3a, 18v, 350khz synchronous step-down converter china resources powtech (shanghai) limited www.crpowtech.com page6 PT1204_dsb rev en0.1 PT1204 package information esop8 d1 e2 b b e 1 b e e 0.25 l l 1 c h 2
3a, 18v, 350khz synchronous step-down converter china resources powtech (shanghai) limited www.crpowtech.com page7 PT1204_dsb rev en0.1 PT1204 b b 1 c 1 c base metal with plating secion b-b millimeters symbol min nom max a 1.75 a1 0.05 0.15 a2 1.30 1.40 1.50 a3 0.60 0.65 0.70 b 0.39 0.48 b1 0.38 0.41 0.43 c 0.21 0.26 c1 0.19 0.20 0.21 d 4.70 4.90 5.10 e 5.80 6.00 6.20 e1 3.70 3.90 4.10 e 1.27(bsc) h 0.25 0.50 l 0.50 0.80 l1 1.05(bsc) 0 8 d1 2.13ref 2.90ref e2 2.13ref 2.00ref
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