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TS3553 3a/350khz synchronous buck dc/dc converter 1/11 version: b11 sop - 8ep general description the TS3553 is a synchronous step-down dc/dc converter that provides wide 4.5v to 23v inpu t voltage range and 3a continuous load current capability. fault pr otection includes cycle-by-cycle current limit, inp ut uvlo, output over voltage protection and thermal shutdown . besides, adjustable soft-start function prevents inrush current at turn-on. this device uses current mode c ontrol scheme that provides fast transient response . in shutdown mode, the regulator draws 1a or less of s upply current. features operating voltage range 4.75v~23v output load current up to 3a high efficiency: up to 95% fixed switching frequency 350khz 100m ? internal power mosfet adjustable output voltage from 0.925~20v stable with low esr output ceramic capacitors current mode operation input under voltage lockout over temperature protection cycle-by cycle current limit <1a shutdown current ordering information part no. package packing TS3553cs rlg sop-8ep 2.5kpcs / 13 reel note: g denote for halogen free product application set-top-box dvd, lcd displays netbook distributed power system dsl modems typical application circuit 3.3v output application circuit pin definition : 1. bs 8. ss 2. vin 7. en 3. sw 6. comp 4. gnd 5. fb
TS3553 3a/350khz synchronous buck dc/dc converter 2/11 version: b11 absolute maximum rating characteristics symbol rating unit maximum supply voltage v in -0.3 ~ +24 v switching pin input voltage v sw -1 ~ (v in +0.3) v boost voltage v bs (v sw -0.3) ~ (v sw +6) v all other pins -0.3 to +6 v output voltage v out 0.925 ~ 20 v power dissipation p d internal limited w operating temperature range t opr -40 to +85 oc storage temperature range t st -65 to +150 oc operating junction temperature range t j +150 oc thermal resistance junction to case jc 15 oc/w thermal resistance junction to ambient ja 40 oc/w note: stresses exceed those rating may damage the d evice note: ja is measured with the pcb copper area of approximat ely 1 in 2 (multi-layer) electrical specifications (t a =25 o c, v in =12v unless otherwise noted) parameter symbol conditions min typ max unit operating voltage v in 4.75 -- 23 v shutdown supply current i sd v en =0v -- 1 3 a feedback voltage v fb 4.75v v in 23v 0.9 0.925 0.95 v load regulation reg load -2 -- +2 % high-side mosfet on-resistance r dson -- 100 -- m ? low-side mosfet on-resistance r dson -- 100 -- m ? high-side mosfet leakage current i l(high-side) v en = 0v, v sw = 0v -- -- 10 a high-side mosfet current limit i limit minimum duty 3.8 -- -- a oscillator frequency f osc 280 350 430 khz short circuit oscillator frequency f sc v fb =0v -- 90 -- khz maximum duty cycle dc v fb =0.8v -- 90 -- % soft-start current i ss v ss =0v -- 6 -- a soft-start period c ss =0.1f -- 15 -- ms en shutdown threshold voltage v ensd v en rising 1.1 1.5 2.0 v thermal shutdown otp -- 160 -- c thermal shutdown hysteresis otp hystersis -- 35 -- c note 1: specifications are production tested at t a =25c. specifications over the -40c to 85c operat ing temperature range are assured by design, characteri zation and correlation with statistical quality con trols (sqc). note 2: it is recommended to use duty ratio above 1 0% for minimizing resultant duty cycle jitter. note 3: it is recommended to connect a soft start c apacitor to soft start pin. leave the soft start pi n open may cause large inrush current and output overshooting
TS3553 3a/350khz synchronous buck dc/dc converter 3/11 version: b11 block diagram pin function description pin no. pin name pin description 1 bs high-side gate drive boost input. bs supplies the d rive for the high-side n-channel mosfet switch. connect a 0.01 f or greater capacitor from sw to bs to power the high side switch. 2 vin power input. in supplies the power to the ic, as we ll as the step-down converter switches. drive in with a 4.75v to 23v power source . bypass in to gnd with a suitably large capacitor to eliminate noise on the input to the ic. see input capacitor. 3 sw power switching output. sw is the switching node th at supplies power to the output. connect the output lc filter from sw to the output load. note that a capacitor is required from sw to bs to power the high-side switc h. 4 gnd ground. 5 fb feedback input. fb senses the output voltage to reg ulate that voltage. drive fb with a resistive voltage divider from the output voltage. the feedback threshold is 0.925v. see setting the output voltage. 6 comp compensation node. comp is used to compensate the r egulation control loop. connect a series rc network from comp to gnd to com pensate the regulation control loop. in some cases, an additional capacitor from c omp to gnd is required. see compensation components. 7 en enable input. en is a 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 with 100k ? resistor for automatic startup. 8 ss soft-start control input. ss controls the soft star t period. connect a capacitor from ss to gnd to set the soft-start period. a 0.1 f capacitor sets the soft-start period to 15ms. to disable the soft-start feature, leave ss unconne cted.
TS3553 3a/350khz synchronous buck dc/dc converter 4/11 version: b11 function description the TS3553 is a constant frequency current mode ste p-down synchronous dc/dc converter. it regulates in put voltage from 4.75v to 23v, down to an output voltag e as low as 0.925v, and can provide 3a of continuou s load current. control loop during normal operation, the output voltage is sens ed at fb pin through a resistive voltage divider an d amplified through the error amplifier. the voltage of error a mplifier output pin C comp is compared to the switc h current to controls the rs latch. at each cycle, the high side nmos would be turned on when the oscillator sets t he rs latch and would be turned off when current comparator res ets the rs latch. when the load current increases, the fb pin voltage drops below 0.925v, it causes the comp volt age increase until average inductor current arrive at new load current. enable the TS3553 en pin provides digital control to turn on/turn off the regulator. when the voltage of en e xceeds the threshold voltage, the regulator starts the soft st art function. if the en pin voltage is below than t he threshold voltage, only the bandgap voltage is alive. if the en pin voltage is below than the shutdown threshold voltage, the regulator will be disable and into the shutdown mod e. maximum load current the maximum load current decreases at lower input v oltage because of large ir drop on the high side sw itch and low side switch. the slope compensation signal redu ces the peak inductor current as a function of the duty cycle to prevent sub-harmonic oscillations at duty cycles gr eater than 50%. output over voltage protection when the fb pin voltage exceeds 20% of the regulati on voltage, the output over voltage protection func tion will discharge the comp pin and the ss pin to gnd, turni ng the high side mosfet off. input under voltage lockout when the TS3553 power on, the internal circuits are held inactive until vin exceeds the input uvlo thr eshold voltage. and the regulator will be disabled when vi n below the input uvlo threshold voltage. the hyste retic of the uvlo comparator is 400 mv. short circuit protection the TS3553 provides short circuit protection functi on to prevent the device damage from short conditio n. when the output short to ground, the oscillator frequency is reduced to prevent the inductor current increasing beyond the current limit. in the meantime, the current limit i s also reduced to lower the short current. once the short condition is removed, the frequency and current limit will retur n to normal. over temperature protection the TS3553 incorporates an over temperature protect ion circuit to protect itself from overheating. whe n the junction temperature exceeds the thermal shutdown t hreshold temperature, the regulator will be shutdow n. compensation the stability of the feedback circuit is controlled through comp pin. the compensation value of the ap plication circuit is optimized for particular requirements. i f different conversions are requires, some of the c omponents may need to be changes to ensure stability .
TS3553 3a/350khz synchronous buck dc/dc converter 5/11 version: b11 application information setting output voltage the output voltage is set using a resistive divider from the output to fb. the fb pin regulated voltag e is 0.925v. thus the output voltage is: r2 recommended value is 10k ? ~30k ? , so r1 is determined by: r1 = 10.81 x (v out C 0.925) k ? recommended component selection v in (v) v out (v) r1 (k ? ) r2 (k ? ) r3 (k ? ) c3 (nf) l1 ( h) c out ( f) 12 5 44.1 10 2.2 3.3 15 10 x 2 5 or 12 3.3 25.7 10 2.2 3.3 10 10 x 2 5 or 12 1.8 9.5 10 2.2 3.3 4.7 10 x 2 5 or 12 1.2 3 10 2.2 3.3 3.3 10 x 2 5 or 12 1 0.81 10 2.2 3.3 2.2 10 x 2 selecting inductor the inductor selection depends on the current rippl e of inductor, the input voltage and the output vol tage. accepting a large current ripple of inductor allows the use of a smaller inductance. however, higher c urrent ripple of inductor can cause higher output ripple voltage and large core loss. by setting an acceptable curre nt ripple of inductor, a suitable inductance can be obtained fro m above formula. in addition, it is important to ensure the inductor saturation current exceeds the peak value of induc tor current in application to prevent core saturation. the peak va lue of inductor current can be calculated according to the following formula. soft-start the TS3553 provides the soft-start function. initia lly, the voltage at ss pin is 0v. then an internal current source of 6 a (typ.) charges an external soft ? -start capacitor. during the soft-start period, the voltage at ss pin will limit the feedback threshold voltage at fb pin. when the volt age at ss pin is higher than 0.925v, the feedback t hreshold voltage at fb pin reaches the desired value. the so ft-start time can be calculated in accordance with the following formula: the soft-start capacitor is discharged to gnd when the en pin is connected to gnd
TS3553 3a/350khz synchronous buck dc/dc converter 6/11 version: b11 application information (continue) optional schottky diode a schottky diode with low forward drop voltage and fast reverse recovery is the ideal choice for bette r efficiency. the forward drop voltage of a schottky diode will r esult in the conduction losses in the diode, and th e diode capacitance (c t or c d ) will cause the switching losses. therefore, it is necessary to consider both forward voltage drop and diode capacitance for diode selection. in addition, the rating of selected schottky diode sho uld be able to handle the input voltage and the maximum peak diode current. input capacitor the output capacitor to prevent the high input voltage ripple and noise resulted from high frequency switching, the use of low esr ceramic capacitor for the maximum rms current is re commended. the approximated rms current of the inpu t capacitor can be calculated according to the follow ing formula. the selection of output capacitor depends on the re quired output voltage ripple. the output voltage ri pple can be expressed as: for lower output voltage ripple, the use of low esr ceramic capacitor is recommended. the tantalum cap acitor can also be used well, but its ers is larger than that of ceramic capacitor. when choosing the input and output ceramic capacito rs, x5r and x7r types are recommended because they retain their capacitance over wider ranges of volta ge and temperature than other types. loop compensation in order to avoid the poor output voltage ripple an d low efficiency caused by instability, TS3553 requ ires a proper external compensation network to compensate its fee dback loop. in this external compensation network, the compensation resistor, rc, and the compensation cap acitor, cc, are used to set the high-frequency inte grator gain and the integrator zero. c7 is used to cancel the z ero caused by the output capacitor and its esr. wh ile using the ceramic capacitor as the output capacitor, c7 can b e omitted due to the small esr. the system has one pole of importance, due to the o utput capacitor, c3//c4 and the load resistor. this poles is located at:
TS3553 3a/350khz synchronous buck dc/dc converter 7/11 version: b11 application information (continue) loop compensation the system has one zero of importance, due to the c ompensation capacitor, cc and the compensation resi stor, rc. this zero is located at: the system may have another zero of importance, if the output capacitor has a large capacitance and/or a high esr value. the zero, due to the esr and capacitance of the output capacitor, is located at: in this case, a third pole set by the compensation capacitor, c7 and the compensation resistor, rc is used to compensate the effect of the esr zero on the loop g ain. this pole is located at: the values of the compensation components given in this data sheet yield a stable control loop for the given output voltage and capacitor. if different conversions and output capacitors are requires, some values of the compensation components may need to be adjusted to ensure stability.
TS3553 3a/350khz synchronous buck dc/dc converter 8/11 version: b11 electrical characteristics curve (t a =25oc, c1=10f, c2=22f, c3=0.1f, l1=10h unless o therwise noted) figure 1. efficiency vs. load current at v in =12v figure 2. start-up waveform at i out =0a figure 3. start-up waveform at i out =3a figure 4. shutdown waveform at i out =0a figure 5. shutdown waveform at i out =3a figure 6. load transient
TS3553 3a/350khz synchronous buck dc/dc converter 9/11 version: b11 electrical characteristics curve (t a =25oc, c1=10f, c2=22f, c3=0.1f, l1=10h unless o therwise noted) figure 7. short circuit waveforms figure 8. short circuit recovery waveforms figure 9. stability waveform at i out =0a figure 10. stability waveform at i out =3a
TS3553 3a/350khz synchronous buck dc/dc converter 10/11 version: b11 sop-8ep mechanical drawing marking diagram y = year code m = month code for halogen free product ( o =jan, p =feb, q =mar, r =apl, s =may, t =jun, u =jul, v =aug, w =sep, x =oct, y =nov, z =dec) l = lot code sop-8ep dimension dim millimeters inches min max min max. a 4.80 5.00 0.189 0.196 b 3.80 4.00 0.150 0.157 c 1.35 1.75 0.054 0.068 d 0.35 0.49 0.014 0.019 e 2.05 2.41 0.081 0.095 e1 2.82 3.30 0.111 0.130 f 0.40 1.25 0.016 0.049 g 1.27bsc 0.05bsc k 0.10 0.25 0.004 0.009 m 0o 7o 0o 7o p 5.80 6.20 0.229 0.244 r 0.25 0.50 0.010 0.019
TS3553 3a/350khz synchronous buck dc/dc converter 11/11 version: b11 notice specifications of the products displayed herein are subject to change without notice. tsc or anyone on its behalf, assumes no responsibility or liability for any erro rs or inaccuracies. information contained herein is intended to provide a product description only. no license, express or implied, to any intellectual property rights is granted by this document. except as provided in tscs terms and co nditions of sale for such products, tsc assumes no liability wh atsoever, and disclaims any express or implied warr anty, relating to sale and/or use of tsc products includi ng liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, cop yright, or other intellectual property right. the products shown herein are not designed for use in medical, life-saving, or life-sustaining applica tions. customers using or selling these products for use i n such applications do so at their own risk and agr ee to fully indemnify tsc for any damages resulting from such i mproper use or sale.

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