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? semiconductor components industries, llc, 2001 january, 2001 rev. 6 1 publication order number: cs5157h/d cs5157h cpu 5-bit synchronous buck controller the cs5157h is a 5bit synchronous dual nchannel buck controller. it is designed to provide unprecedented transient response for today's demanding highdensity, highspeed logic. the regulator operates using a proprietary control method, which allows a 100 ns response time to load transients. the cs5157h is designed to operate over a 4.2520 v range (v cc ) using 12 v to power the ic and 5.0 v or 12 v as the main supply for conversion. the cs5157h is specifically designed to power pentium ? ii processors and other high performance core logic. it includes the following features: on board, 5bit dac, short circuit protection, 1.0% output tolerance, v cc monitor, and programmable soft start capability. the cs5157h is available in 16 pin surface mount. features ? dual nchannel design ? excess of 1.0 mhz operation ? 100 ns transient response ? 5bit dac ? 30 ns gate rise/fall times ? 1.0% dac accuracy ? 5.0 v & 12 v operation ? remote sense ? programmable soft start ? lossless short circuit protection ? v cc monitor ? 25 ns fet nonoverlap time ? v 2 ? control topology ? current sharing ? overvoltage protection cs5157hgdr16 http://onsemi.com a = assembly location wl, l = wafer lot yy, y = year ww, w = work week device package shipping ordering information cs5157hgd16 so16 48 units/rail so16 2500 tape & reel soic16 d suffix case 751b pin connections 1 cs5157h awlyww 16 marking diagram 1 16 v cc2 v ffb 1 16 v gate(h) c off pgnd v id4 v gate(l) ss v cc1 v id3 lgnd v id2 comp v id1 v fb v id0
cs5157h http://onsemi.com 2 figure 1. application diagram, switching power supply for core logic pentium ii processor comp v ffb v fb v gate(h) v cc2 v cc1 v id0 v id1 v id2 v id3 pgnd ss c off cs5157h aiei 12 v 330 pf 0.1 m f lgnd 1200 m f/10 v 3 0.1 m f 1.3 v to 3.5 v @ 13 a v id0 v id1 v id2 v id3 aiei 1200 m f/10 v 5 2.0 m h irl3103 0.33 m f 5.0 v 3.3 k 100 pf v id4 v id4 irl3103 v gate(l) absolute maximum ratings* rating value unit operating junction temperature, t j 0 to 150 c lead temperature soldering: reflow: (smd styles only) (note 1.) 230 peak c storage temperature range, t s 65 to +150 c esd susceptibility (human body model) 2.0 kv 1. 60 second maximum above 183 c. *the maximum package power dissipation must be observed. absolute maximum ratings pin name max operating voltage max current v cc1 16 v/0.3 v 25 ma dc/1.5 a peak v cc2 20 v/0.3 v 20 ma dc/1.5 a peak ss 6.0 v/0.3 v 100 m a comp 6.0 v/0.3 v 200 m a v fb 6.0 v/0.3 v 0.2 m a c off 6.0 v/0.3 v 0.2 m a v ffb 6.0 v/0.3 v 0.2 m a v id0 v id4 6.0 v/0.3 v 50 m a v gate(h) 20 v/0.3 v 100 ma dc/1.5 a peak v gate(l) 16 v/0.3 v 100 ma dc/1.5 a peak lgnd 0 v 25 ma pgnd 0 v 100 ma dc/1.5 a peak
cs5157h http://onsemi.com 3 electrical characteristics (0 c < t a < +70 c; 0 c < t j < +125 c; 8.0 v < v cc1 < 14 v; 5.0 v < v cc2 < 20 v;dac code: v id4 = v id2 = v id1 = v id0 = 1; v id3 = 0 ; cv gate(l) and cv gate(h) = 1.0 nf; c off = 330 pf; c ss = 0.1 m f, unless otherwise specified.) characteristic test conditions min typ max unit error amplifier v fb bias current v fb = 0 v 0.3 1.0 m a open loop gain 1.25 v < v comp < 4.0 v; note 2. 50 60 db unity gain bandwidth note 2. 500 3000 khz comp sink current v comp = 1.5 v; v fb = 3.0 v; v ss > 2.0 v 0.4 2.5 8.0 ma comp source current v comp = 1.2 v; v fb = 2.7 v; v ss = 5.0 v 30 50 80 m a comp clamp current v comp = 0 v; v fb = 2.7 v 0.4 1.0 1.6 ma comp high voltage v fb = 2.7 v; v ss = 5.0 v 4.0 4.3 5.0 v comp low voltage v fb = 3.0 v 160 600 mv psrr 8.0 v < v cc1 < 14 v @ 1.0 khz; note 2. 60 85 db v cc1 monitor start threshold output switching 3.75 3.90 4.05 v stop threshold output not switching 3.70 3.85 4.00 v hysteresis startstop 50 mv v gate(h) and v gate(l) out source sat at 100 ma measure v cc1 v gate(l) ; v cc2 v gate(h) 1.2 2.0 v out sink sat at 100 ma measure v gate(h) v pgnd ; v gate(l) v pgnd 1.0 1.5 v out rise time 1.0 v < v gate(h) < 9.0 v; 1.0 v < v gate(l) < 9.0 v; v cc1 = v cc2 = 12 v 30 50 ns out fall time 9.0 v > v gate(h) > 1.0 v; 9.0 v > v gate(l) > 1.0 v; v cc1 = v cc2 = 12 v 30 50 ns delay v gate(h) to v gate(l) v gate(h) falling to 2.0 v; v cc1 = v cc2 = 8.0 v; v gate(l) rising to 2.0 v 25 50 ns delay v gate(l) to v gate(h) v gate(l) falling to 2.0 v; v cc1 = v cc2 = 8.0 v; v gate(h) rising to 2.0 v 25 50 ns v gate(h) , v gate(l) resistance resistor to lgnd. note 2. 20 50 100 k w v gate(h) , v gate(l) schottky lgnd to v gate(h) @ 10 ma lgnd to v gate(l) @ 10 ma 600 800 mv soft start (ss) charge time 1.6 3.3 5.0 ms pulse period 25 100 200 ms duty cycle (charge time /pulse period) 100 1.0 3.3 6.0 % comp clamp voltage v fb = 0 v; v ss = 0 0.50 0.95 1.10 v v ffb ss fault disable v gate(h) = low; v gate(l) = low 0.9 1.0 1.1 v high threshold 2.5 3.0 v pwm comparator transient response v ffb = 0 to 5.0 v to v gate(h) = 9.0 v to 1.0 v; v cc1 = v cc2 = 12 v 100 125 ns v ffb bias current v ffb = 0 v 0.3 m a 2. guaranteed by design, not 100% tested in production.
cs5157h http://onsemi.com 4 electrical characteristics (continued) (0 c < t a < +70 c; 0 c < t j < +125 c; 8.0 v < v cc1 < 14 v; 5.0 v < v cc2 < 20 v;dac code: v id4 = v id2 = v id1 = v id0 = 1; v id3 = 0 ; cv gate(l) and cv gate(h) = 1.0 nf; c off = 330 pf; c ss = 0.1 m f, unless otherwise specified.) characteristic unit max typ min test conditions dac input threshold v id0, v id1 , v id2 , v id3 , v id4 1.00 1.25 2.40 v input pull up resistance v id0, v id1 , v id2 , v id3 , v id4 25 50 100 k w pull up voltage 4.85 5.00 5.15 v accuracy (all codes except 1 1111) measure v fb = v comp , 25 c t j 125 c 1.0 % v id4 v id3 v id2 v id1 v id0 0 1 1 1 1 1.2870 1.3000 1.3130 v 0 1 1 1 0 1.3365 1.3500 1.3635 v 0 1 1 0 1 1.3860 1.4000 1.4140 v 0 1 1 0 0 1.4355 1.4500 1.4645 v 0 1 0 1 1 1.4850 1.5000 1.5150 v 0 1 0 1 0 1.5345 1.5500 1.5655 v 0 1 0 0 1 1.5840 1.6000 1.6160 v 0 1 0 0 0 1.6335 1.6500 1.6665 v 0 0 1 1 1 1.6830 1.7000 1.7170 v 0 0 1 1 0 1.7325 1.7500 1.7675 v 0 0 1 0 1 1.7820 1.8000 1.8180 v 0 0 1 0 0 1.8315 1.8500 1.8685 v 0 0 0 1 1 1.8810 1.9000 1.9190 v 0 0 0 1 0 1.9305 1.9500 1.9695 v 0 0 0 0 1 1.9800 2.0000 2.0200 v 0 0 0 0 0 2.0295 2.0500 2.0705 v 1 1 1 1 1 1.2191 1.2440 1.2689 v 1 1 1 1 0 2.0790 2.1000 2.1210 v 1 1 1 0 1 2.1780 2.2000 2.2220 v 1 1 1 0 0 2.2770 2.3000 2.3230 v 1 1 0 1 1 2.3760 2.4000 2.4240 v 1 1 0 1 0 2.4750 2.5000 2.5250 v 1 1 0 0 1 2.5740 2.6000 2.6260 v 1 1 0 0 0 2.6730 2.7000 2.7270 v 1 0 1 1 1 2.7720 2.8000 2.8280 v 1 0 1 1 0 2.8710 2.9000 2.9290 v 1 0 1 0 1 2.9700 3.0000 3.0300 v 1 0 1 0 0 3.0690 3.1000 3.1310 v 1 0 0 1 1 3.1680 3.2000 3.2320 v 1 0 0 1 0 3.2670 3.3000 3.3330 v 1 0 0 0 1 3.3660 3.4000 3.4340 v 1 0 0 0 0 3.4650 3.5000 3.5350 v
cs5157h http://onsemi.com 5 electrical characteristics (continued) (0 c < t a < +70 c; 0 c < t j < +125 c; 8.0 v < v cc1 < 14 v; 5.0 v < v cc2 < 20 v;dac code: v id4 = v id2 = v id1 = v id0 = 1; v id3 = 0 ; cv gate(l) and cv gate(h) = 1.0 nf; c off = 330 pf; c ss = 0.1 m f, unless otherwise specified.) characteristic unit max typ min test conditions supply current i cc1 no switching 8.5 13.5 ma i cc2 no switching 1.6 3.0 ma operating i cc1 v fb = comp = v ffb 8.0 13 ma operating i cc2 v fb = comp = v ffb 2.0 5.0 ma c off normal charge time v ffb = 1.5 v; v ss = 5.0 v 1.0 1.6 2.2 m s extension charge time v ss = v ffb = 0 5.0 8.0 11.0 m s discharge current c off to 5.0 v; v fb > 1.0 v 5.0 ma time out timer time out time v fb = v comp ; v ffb = 2.0 v; record v gate(h) pulse high duration 10 30 65 m s fault mode duty cycle v ffb = 0v 35 50 70 % package pin description package pin # so16 pin symbol function 1, 2, 3, 4, 6 v id0 v id4 voltage id dac input pins. these pins are internally pulled up to 5.0 v providing logic ones if left open. v id4 selects the dac range. when v id4 is high (logic one), the dac range is 2.10 v to 3.50 v with 100 mv increments. when v id4 is low (logic zero), the dac range is 1.30 v to 2.05 v with 50 mv increments. v id0 v id4 select the desired dac output voltage. leaving all 5 dac input pins open results in a dac output voltage of 1.2440 v, allowing for adjustable output voltage, using a traditional resistor divider. 5 ss soft start pin. a capacitor from this pin to lgnd in conjunction with internal 60 m a cur- rent source provides soft start function for the controller. this pin disables fault detect function during soft start. when a fault is detected, the soft start capacitor is slowly dis- charged by internal 2.0 m a current source setting the time out before trying to restart the ic. charge/discharge current ratio of 30 sets the duty cycle for the ic when the regulator output is shorted. 7 c off a capacitor from this pin to ground sets the time duration for the on board one shot, which is used for the constant off time architecture. 8 v ffb fast feedback connection to the pwm comparator. this pin is connected to the regulator output. the inner feedback loop terminates on time. 9 v cc2 boosted power for the high side gate driver. 10 v gate(h) high fet driver pin capable of 1.5 a peak switching current. internal circuit prevents v gate(h) and v gate(l) from being in high state simultaneously. 11 pgnd high current ground for the ic. the mosfet driver is referenced to this pin. input capac- itor ground and the source of lower fet should be tied to this pin. 12 v gate(l) low fet driver pin capable of 1.5 a peak switching current. 13 v cc1 input power for the ic and low side gate driver. 14 lgnd signal ground for the ic. all control circuits are referenced to this pin. 15 comp error amplifier compensation pin. a capacitor to ground should be provided externally to compensate the amplifier. 16 v fb error amplifier dc feedback input. this is the master voltage feedback which sets the output voltage. this pin can be connected directly to the output or a remote sense trace.
cs5157h http://onsemi.com 6 figure 2. block diagram + + + v cc1 ss v id0 v id1 v id2 v id3 v id4 v ffb low comparator v ffb fast feedback lgnd slow feedback pwm comparator ss low comparator ss high comparator 5 bit dac v cc1 monitor comparator error amplifier v cc1 v cc2 c off v gate(h) v gate(l) pgnd fault fault fault latch pgnd r s q q r s q q r s q latch pmw c off one shot offtime timeout timeout timer edge triggered extended offtime timeout normal offtime timeout maximum ontime timeout (30 m s) gate(h) = on gate(h) = off 2.0 m a 60 m a 5.0 v 0.7 v 2.5 v 1.0 v + + + 3.90 v 3.85v v fb comp pwm comp applications information theory of operation v 2 control method the v 2 method of control uses a ramp signal that is generated by the esr of the output capacitors. this ramp is proportional to the ac current through the main inductor and is offset by the value of the dc output voltage. this control scheme inherently compensates for variation in either line or load conditions, since the ramp signal is generated from the output voltage itself. this control scheme inherently compensates for variation in either line or load conditions, since the ramp signal is generated from the output voltage itself. this control scheme differs from traditional techniques such as voltage mode, which generates an artificial ramp, and current mode, which generates a ramp from inductor current. figure 3. v 2 control diagram comp v ffb reference voltage + + pwm comparator ramp signal error amplifier error signal output voltage feedback v fb v gate(l) e c v gate(h)
cs5157h http://onsemi.com 7 the v 2 control method is illustrated in figure 3. the output voltage is used to generate both the error signal and the ramp signal. since the ramp signal is simply the output voltage, it is affected by any change in the output regardless of the origin of that change. the ramp signal also contains the dc portion of the output voltage, which allows the control circuit to drive the main switch to 0% or 100% duty cycle as required. a change in line voltage changes the current ramp in the inductor, affecting the ramp signal, which causes the v 2 control scheme to compensate the duty cycle. since the change in inductor current modifies the ramp signal, as in current mode control, the v 2 control scheme has the same advantages in line transient response. a change in load current will have an affect on the output voltage, altering the ramp signal. a load step immediately changes the state of the comparator output, which controls the main switch. load transient response is determined only by the comparator response time and the transition speed of the main switch. the reaction time to an output load step has no relation to the crossover frequency of the error signal loop, as in traditional control methods. the error signal loop can have a low crossover frequency, since transient response is handled by the ramp signal loop. the main purpose of this `slow' feedback loop is to provide dc accuracy. noise immunity is significantly improved, since the error amplifier bandwidth can be rolled off at a low frequency. enhanced noise immunity improves remote sensing of the output voltage, since the noise associated with long feedback traces can be effectively filtered. line and load regulation are drastically improved because there are two independent voltage loops. a voltage mode controller relies on a change in the error signal to compensate for a deviation in either line or load voltage. this change in the error signal causes the output voltage to change corresponding to the gain of the error amplifier, which is normally specified as line and load regulation. a current mode controller maintains fixed error signal under deviation in the line voltage, since the slope of the ramp signal changes, but still relies on a change in the error signal for a deviation in load. the v 2 method of control maintains a fixed error signal for both line and load variation, since the ramp signal is affected by both line and load. constant off time to maximize transient response, the cs5157h uses a constant off time method to control the rate of output pulses. during normal operation, the off time of the high side switch is terminated after a fixed period, set by the c off capacitor. to maintain regulation, the v 2 control loop varies switch on time. the pwm comparator monitors the output voltage ramp, and terminates the switch on time. constant off time provides a number of advantages. switch duty cycle can be adjusted from 0 to 100% on a pulse by pulse basis when responding to transient conditions. both 0% and 100% duty cycle operation can be maintained for extended periods of time in response to load or line transients. pwm slope compensation to avoid subharmonic oscillations at high duty cycles is avoided. switch on time is limited by an internal 25 m s timer, minimizing stress to the power components. programmable output the cs5157h is designed to provide two methods for programming the output voltage of the power supply. a five bit on board digital to analog converter (dac) is used to program the output voltage within two different ranges. the first range is 2.10 v to 3.50 v in 100 mv steps, the second is 1.30 v to 2.05 v in 50 mv steps, depending on the digital input code. if all five bits are left open, the cs5157h enters adjust mode. in adjust mode, the designer can choose any output voltage by using resistor divider feedback to the v fb and v ffb pins, as in traditional controllers. start up until the voltage on the v cc1 supply pin exceeds the 3.9 v monitor threshold, the soft start and gate pins are held low. the fault latch is reset (no fault condition). the output of the error amplifier (comp) is pulled up to 1.0 v by the comparator clamp. when the v cc1 pin exceeds the monitor threshold, the gate(h) output is activated, and the soft start capacitor begins charging. the gate(h) output will remain on, enabling the nfet switch, until terminated by either the pwm comparator, or the maximum on time timer. if the maximum on time is exceeded before the regulator output voltage achieves the 1.0 v level, the pulse is terminated. the gate(h) pin drives low, and the ga te(l) pin drives high for the duration of the extended off time. this time is set by the time out timer and is approximately equal to the maximum on time, resulting in a 50% duty cycle. the gate(l) pin will then drive low, the gate(h) pin will drive high, and the cycle repeats. when regulator output voltage achieves the 1.0 v level present at the comp pin, regulation has been achieved and normal off time will ensue. the pwm comparator terminates the switch on time, with off time set by the c off capacitor. the v 2 control loop will adjust switch duty cycle as required to ensure the regulator output voltage tracks the output of the error amplifier. the soft start and comp capacitors will charge to their final levels, providing a controlled turn on of the regulator output. regulator turn on time is determined by the comp capacitor charging to its final value. its voltage is limited by
cs5157h http://onsemi.com 8 the soft start comp clamp and the voltage on the soft start pin (see figures 4 and 5). figure 4. cs5157h demonstration board startup in response to increasing 12 v and 5.0 v input voltages. extended off time is followed by normal off time operation when output voltage achieves regulation to the error amplifier output. m 250 m s trace 3 12 v input (v cc1 and v cc2 ) (5.0 v/div.) trace 1 regulator output voltage (1.0 v/div.) trace 4 5.0 v input (1.0 v/div.) trace 2 inductor switching node (2.0 v/div.) figure 5. cs5157h demonstration board startup waveforms m 2.50 ms trace 3 comp pin (error amplifier output) (1.0 v/div.) trace 1 regulator output voltage (1.0 v/div.) trace 4 soft start pin (2.0 v/div.) if the input voltage rises quickly, or the regulator output is enabled externally, output voltage will increase to the level set by the error amplifier output more rapidly, usually within a couple of cycles (see figure 6). figure 6. cs5157h demonstration board enable startup waveforms m 10.0 m s trace 1 regulator output voltage (5.0 v/div.) trace 2 inductor switching node (5.0 v/div.) normal operation during normal operation, switch off time is constant and set by the c off capacitor. switch on time is adjusted by the v 2 control loop to maintain regulation. this results in changes in regulator switching frequency, duty cycle, and output ripple in response to changes in load and line. output voltage ripple will be determined by inductor ripple current working into the esr of the output capacitors (see figures 7 and 8). figure 7. peaktopeak ripple on v out = 2.8 v, i out = 0.5 a (light load) m 1.00 m s trace 1 regulator output voltage (10 mv/div.) trace 2 inductor switching node (5.0 v/div.)
cs5157h http://onsemi.com 9 figure 8. peaktopeak ripple on v out = 2.8 v, i out = 13 a (heavy load) m 1.00 m s trace 1 regulator output voltage (10 mv/div.) trace 2 inductor switching node (5.0 v/div.) transient response the cs5157h v 2 control loop's 100 ns reaction time provides unprecedented transient response to changes in input voltage or output current. pulse by pulse adjustment of duty cycle is provided to quickly ramp the inductor current to the required level. since the inductor current cannot be changed instantaneously, regulation is maintained by the output capacitor(s) during the time required to slew the inductor current. for best transient response, a combination of a number of high frequency and bulk output capacitors are usually used. if the maximum on time is exceeded while responding to a sudden increase in load current, a normal off time occurs to prevent saturation of the output inductor. figure 9. cs5157h demonstration board response to a 0.5 to 13 a load pulse (output set for 2.8 v) trace 2 regulator output voltage (10 a/div.) trace 1 regulator output voltage (100 mv/div.) figure 10. cs5157h demonstration board response to 13 a load turn on (output set for 2.8 v). upon completing a normal off time, the v 2 control loop immediately connects the inductor to the input voltage, providing 100% duty cycle. regulation is achieved in less than 20 s trace 1 regulator output voltage (100 mv/div.) trace 2 inductor switching node (5.0 v/div.) trace 3 output current (0.5 to 13 amps) (10 a/div.) figure 11. cs5157h demonstration board response to 13 a load turn off (output set for 2.8 v). v 2 control topology immediately connects inductor to ground, providing 0% duty cycle. regulation is achieved in less than 10 s trace 3 output current (13 to 0,5 amps) (10 a/div.) trace 2 inductor switching node (5.0 v/div.) trace 1 regulator output voltage (100 mv/div.) protection and monitoring features v cc1 monitor to maintain predictable startup and shutdown characteristics an internal v cc1 monitor circuit is used to prevent the part from operating below 3.75 v minimum startup. the v cc1 monitor comparator provides hysteresis and guarantees a 3.70 v minimum shutdown threshold.
cs5157h http://onsemi.com 10 short circuit protection a lossless hiccup mode short circuit protection feature is provided, requiring only the soft start capacitor to implement. if a short circuit c ondition occurs (v ffb < 1.0 v), the v ffb low comparator sets the fault latch. this causes the mosfet to shut off, disconnecting the regulator from it's input voltage. the soft start capacitor is then slowly discharged by a 2.0 m a current source until it reaches it's lower 0.7 v threshold. the regulator will then attempt to restart normally, operating in it's extended off time mode with a 50% duty cycle, while the soft start capacitor is charged with a 60 m a charge current. if the short circuit condition persists, the regulator output will not achieve the 1.0 v low v ffb comparator threshold before the soft start capacitor is charged to it's upper 2.5 v threshold. if this happens the cycle will repeat itself until the short is removed. the soft start charge/discharge current ratio sets the duty cycle for the pulses (2.0 m a/60 m a = 3.3%), while actual duty cycle is half that due to the extended off time mode (1.65%). this protection feature results in less stress to the regulator components, input power supply, and pc board traces than occurs with constant current limit protection (see figures 12 and 13). if the short circuit condition is removed, output voltage will rise above the 1.0 v level, preventing the fault latch from being set, allowing normal operation to resume. figure 12. cs5157h demonstration board hiccup mode short circuit protection. gate pulses are delivered while the soft start capacitor charges, and cease during discharge m 25.0 ms trace 3 soft start timing capacitor (1.0 v/div.) trace 4 5.0 v supply voltage (2.0 v/div.) trace 2 inductor switching node (2.0 v/div.) figure 13. startup with regulator output shorted m 50.0 m s trace 4 5.0 v from pc power supply (2.0 v/div.) trace 2 inductor switching node (2.0 v/div.) overvoltage protection overvoltage protection (ovp) is provided as result of the normal operation of the v 2 control topology and requires no additional external components. the control loop responds to an overvoltage condition within 100 ns, causing the top mosfet to shut off, disconnecting the regulator from it's input voltage. the bottom mosfet is then activated, resulting in a acrowbaro action to clamp the output voltage and prevent damage to the load (see figures 14 and 15 ). the regulator will remain in this state until the overvoltage condition ceases or the input voltage is pulled low. the bottom fet and board trace must be properly designed to implement the ovp function. figure 14. ovp response to an inputtooutput short circuit by immediately providing 0% duty cycle, crowbarring the input voltage to ground m 10.0 m s trace 1 regulator output voltage (1.0 v/div.) trace 2 inductor switching node (5.0 v/div.) trace 4 5.0 v from pc power supply (5.0 v/div.)
cs5157h http://onsemi.com 11 figure 15. ovp response to an inputtooutput short circuit by pulling the input voltage to ground m 5.00 ms trace 1 regulator output voltage (1.0 v/div.) trace 4 5.0 v from pc power supply (2.0 v/div.) external output enable circuit on/off control of the regulator can be implemented through the addition of two additional discrete components (see figure 16). this circuit operates by pulling the soft start pin high, and the v ffb pin low, emulating a short circuit condition. figure 16. implementing shutdown with the cs5157h shutdown input 5.0 v mmun2111t1 (sot23) 5 8 v ffb ss in4148 cs5157h external power good circuit an optional power good signal can be generated through the use of four additional external components (see figure 17). the threshold voltage of the power good signal can be adjusted per the following equation: v power good (r1 r2) 0.65 v r2 this circuit provides an open collector output that drives the power good output to ground for regulator voltages less than v power good . figure 17. implementing power good with the cs5157h 5.0 v power good 10 k v out pn3904 6.2 k r1 r2 pn3904 10 k r3 cs5157h figure 18. cs5157h demonstration board during power up. power good signal is activated when output voltage reaches 1.70 v. m 2.50 ms trace 4 5.0 v input (2.0 v/div.) trace 3 12 v input (v cc1 ) and (v cc2 ) (10 v/div.) trace 1 regulator output voltage (1.0 v/div.) trace 2 power good signal (2.0 v/div.) selecting external components the cs5157h can be used with a wide range of external power components to optimize the cost and performance of a particular design. the following information can be used as general guidelines to assist in their selection. nfet power transistors both logic level and standard mosfets can be used. the reference designs derive gate drive from the 12 v supply which is generally available in most computer systems and utilize logic level mosfets. multiple mosfets may be paralleled to reduce losses and improve efficiency and thermal management. voltage applied to the mosfet gates depends on the application circuit used. both upper and lower gate driver outputs are specified to drive to within 1.5 v of ground when in the low state and to within 2.0 v of their respective bias supplies when in the high state. in practice, the mosfet gates will be driven rail to rail due to overshoot caused by the
cs5157h http://onsemi.com 12 capacitive load they present to the controller ic. for the typical application where v cc1 = v cc2 = 12 v and 5.0 v is used as the source for the regulator output current, the following gate drive is provided; v gate(h) 12 v 5.0 v 7.0 v, v gate(l) 12 v (see figure 19.) figure 19. cs5157h gate drive waveforms depicting rail to rail swing m 1.00 m s math 1 = v gate(h) 5.0 v in trace 3 = v gate(h) (10 v/div.) trace 4 = v gate(l) (10 v/div.) trace 2 inductor switching nodes (5.0 v/div.) the most important aspect of mosfet performance is rds on , which effects regulator efficiency and mosfet thermal management requirements. the power dissipated by the mosfets may be estimated as follows; switching mosfet: power i load 2 rds on duty cycle synchronous mosfet: power i load 2 rds on ( 1 duty cycle ) duty cycle = v out (i load rds on of synch fet ) v in (i load rds on of synch fet ) (i load rds on of switch fet ) off time capacitor (c off ) the c off timing capacitor sets the regulator off time: t off c off 4848.5 when the v ffb pin is less than 1.0 v, the current char ging the c off capacitor is reduced. the extended off time can be calculated as follows: t off c off 24, 242.5 off time will be determined by either the t off time, or the time out timer, whichever is longer. the preceding equations for duty cycle can also be used to calculate the regulator switching frequency and select the c off timing capacitor: c off perioid ( 1 duty cycle ) 4848.5 where: period 1 switching frequency schottky diode for synchronous mosfet a schottky diode may be placed in parallel with the synchronous mosfet to conduct the inductor current upon turn off of the switching mosfet to improve efficiency. the cs5157h reference circuit does not use this device due to it's excellent design. instead, the body diode of the synchronous mosfet is utilized to reduce cost and conducts the inductor current. for a design operating at 200 khz or so, the low nonoverlap time combined with schottky forward recovery time may make the benefits of this device not worth the additional expense (see figure 8, channel 2). the power dissipation in the synchronous mosfet due to body diode conduction can be estimated by the following equation: p ower v bd i load conduction time switching frequenc y where v bd = the forward drop of the mosfet body diode. for the cs5157h demonstration board as shown in figure 8; power 1.6 v 13 a 100 ns 233 khz 0.48 w this is only 1.3% of the 36.4 w being delivered to the load. input and output capacitors these components must be selected and placed carefully to yield optimal results. capacitors should be chosen to provide acceptable ripple on the input supply lines and regulator output voltage. key specifications for input capacitors are their ripple rating, while esr is important for output capacitors. for best transient response, a combination of low value/high frequency and bulk capacitors placed close to the load will be required. output inductor the inductor should be selected based on its inductance, current capability, and dc resistance. increasing the inductor value will decrease output voltage ripple, but degrade transient response. thermal management thermal considerations for power mosfets and diodes in order to maintain good reliability, the junction temperature of the semiconductor components should be kept to a maximum of 150 c or lower. the thermal
cs5157h http://onsemi.com 13 impedance (junction to ambient) required to meet this requirement can be calculated as follows: thermal impedance t junction(max) t ambient power a heatsink may be added to to220 components to reduce their thermal impedance. a number of pc board layout techniques such as thermal vias and additional copper foil area can be used to improve the power handling capability of surface mount components. emi management as a consequence of large currents being turned on and off at high frequency, switching regulators generate noise as a consequence of their normal operation. when designing for compliance with emi/emc regulations, additional components may be added to reduce noise emissions. these components are not required for regulator operation and experimental results may allow them to be eliminated. the input filter inductor may not be required because bulk filter and bypass capacitors, as well as other loads located on the board will tend to reduce regulator di/dt effects on the circuit board and input power supply. placement of the power component to minimize routing distance will also help to reduce emissions. figure 20. filter components 1000 pf 33 w 2.0 m h figure 21. input filter 1200 pf 3.0/16 v 2.0 m h + layout guidelines 1. place 12 v filter capacitor next to the ic and connect capacitor ground to pin 11 (pgnd). 2. connect pin 11 (pgnd) with a separate trace to the ground terminals of the 5.0 v input capacitors. 3. place fast feedback filter capacitor next to pin 8 (v ffb ) and connect it's ground terminal with a separate, wide trace directly to pin 14 (lgnd). 4. connect the ground terminals of the compensation capacitor directly to the ground of the fast feedback filter capacitor to prevent common mode noise from effecting the pwm comparator. 5. place the output filter capacitor(s) as close to the load as possible and connect the ground terminal to pin 14 (lgnd). 6. connect the v fb pin directly to the load with a separate trace (remote sense). 7. place 5.0 v input capacitors close to the switching mosfet and synchronous mosfet. route gate drive signals v gate(h) (pin 10) and v gate(l) (pin 12 when used) with traces that are a minimum of 0.025 inches wide. figure 22. layout guidelines to the negative terminal of the output capacitors v cc 100 pf 0.1 m f soft start off time v comp to the negative terminal of the input capacitors 15 11 5 8 v ffb 1.0 m f
cs5157h http://onsemi.com 14 comp v ffb v fb v gate(h) v gate(l) v cc2 v cc1 v id0 v id1 v id2 v id3 v id4 pgnd ss c off cs5157h 3.3 v 330 pf 0.33 m f lgnd 33 m f/25 v 3 5.0 m h si9410 1.0 m f 3.3 k 0.1 m f 100 pf 12 v 2.5 v/7.0 a 100 m f/10 v 2 tantalum si9410 tantalum + + figure 23. additional application diagram, 5.0 v to 3.3 v/10 a converter comp v ffb v fb v gate(h) v gate(l) v cc2 v cc1 v id0 v id1 v id2 v id3 v id4 pgnd ss c off cs5157h si4410dy si9410dy tantalum tantalum 3.3 v/10 a 5.0v 0.1 m f 330 pf 0.1 m f 0.33 m f lgnd 100 pf 3.3 k 100 m f/10 v 3 1.0 m f 1.0 m f mbrs120 mbrs120 100 m f/10 v 3 1.0 m f mbrs 120 3.0 m h + + figure 24. additional application diagram, 3.3 v to 2.5 v/7.0 a converter with 12 v bias
cs5157h http://onsemi.com 15 figure 25. additional application diagram, 5.0 v to 3.3 v/10 a converter with current sharing comp v ffb v fb v gate(h) v gate(l) v cc2 v cc1 v id0 v id1 v id2 v id3 v id4 pgnd ss c off cs5157h si4410 si9410 tantalum tantalum 3.3 v/10 a 10 w 5.0v 0.1 m f 330 pf 0.1 m f 0.33 m f lgnd 100 pf 3.3 k 100 m f/10 v 3 connect to other circuits for current sharing 1.0 m f 1.0 m f mbrs120 mbrs120 100 m f/10 v 3 1.0 m f remote sense mbrs 120 3.0 m h + + comp v ffb v fb v gate(h) v gate(l) v cc2 v cc1 v id0 v id1 v id2 v id3 v id4 pgnd ss c off cs5157h 330 pf 0.33 m f lgnd 820 m f/16 v 4 1.1 m h 1n4746 1.0 m f 3.3 k 0.1 m f 100 pf 12 v 3.3 v/5.0 a 1200 m f/10 v 2 aluminum electrolytic fy10aaj03 18 v + + figure 26. additional application diagram, 12 v to 3.3 v/5.0 a converter with remote sense 12 v fy10aaj03 fy10aaj03 aluminum electrolytic 1.0 w 1/4 w 1n5818 1n5818 22 w 0.1 m f 1.0 m f
cs5157h http://onsemi.com 16 package dimensions notes: 1. dimensioning and tolerancing per ansi y14.5m, 1982. 2. controlling dimension: millimeter. 3. dimensions a and b do not include mold protrusion. 4. maximum mold protrusion 0.15 (0.006) per side. 5. dimension d does not include dambar protrusion. allowable dambar protrusion shall be 0.127 (0.005) total in excess of the d dimension at maximum material condition. 18 16 9 seating plane f j m r x 45 g 8 pl p b a m 0.25 (0.010) b s t d k c 16 pl s b m 0.25 (0.010) a s t dim min max min max inches millimeters a 9.80 10.00 0.386 0.393 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 f 0.40 1.25 0.016 0.049 g 1.27 bsc 0.050 bsc j 0.19 0.25 0.008 0.009 k 0.10 0.25 0.004 0.009 m 0 7 0 7 p 5.80 6.20 0.229 0.244 r 0.25 0.50 0.010 0.019 so16 d suffix case 751b05 issue j package thermal data parameter 16so unit r q jc typical 28 c/w r q ja typical 115 c/w
cs5157h http://onsemi.com 17 notes
cs5157h http://onsemi.com 18 notes
cs5157h http://onsemi.com 19 notes
cs5157h http://onsemi.com 20 on semiconductor and are trademarks of semiconductor components industries, llc (scillc). scillc reserves the right to make changes without further notice to any products herein. scillc makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does scillc assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. atypicalo parameters which may be provided in scill c data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. all operating parameters, including atypicalso must be validated for each customer application by customer's technical experts. scillc does not convey any license under its patent rights nor the rights of others. scillc products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body , or other applications intended to support or sustain life, or for any other application in which the failure of the scillc product could create a sit uation where personal injury or death may occur. should buyer purchase or use scillc products for any such unintended or unauthorized application, buyer shall indemnify and hold scillc and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthori zed use, even if such claim alleges that scillc was negligent regarding the design or manufacture of the part. scillc is an equal opportunity/affirmative action employer. publication ordering information central/south america: spanish phone : 3033087143 (monfri 8:00am to 5:00pm mst) email : onlitspanish@hibbertco.com asia/pacific : ldc for on semiconductor asia support phone : 3036752121 (tuefri 9:00am to 1:00pm, hong kong time) toll free from hong kong & singapore: 00180044223781 email : onlitasia@hibbertco.com japan : on semiconductor, japan customer focus center 4321 nishigotanda, shinagawaku, tokyo, japan 1410031 phone : 81357402745 email : r14525@onsemi.com on semiconductor website : http://onsemi.com for additional information, please contact your local sales representative. cs5157h/d v 2 is a trademark of switch power, inc. pentium is a registered trademark of intel corporation. north america literature fulfillment : literature distribution center for on semiconductor p.o. box 5163, denver, colorado 80217 usa phone : 3036752175 or 8003443860 toll free usa/canada fax : 3036752176 or 8003443867 toll free usa/canada email : onlit@hibbertco.com fax response line: 3036752167 or 8003443810 toll free usa/canada n. american technical support : 8002829855 toll free usa/canada europe: ldc for on semiconductor european support german phone : (+1) 3033087140 (monfri 2:30pm to 7:00pm cet) email : onlitgerman@hibbertco.com french phone : (+1) 3033087141 (monfri 2:00pm to 7:00pm cet) email : onlitfrench@hibbertco.com english phone : (+1) 3033087142 (monfri 12:00pm to 5:00pm gmt) email : onlit@hibbertco.com european tollfree access*: 0080044223781 *available from germany, france, italy, uk, ireland

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