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june 2000 1 mic2182 mic2182 micrel mic2182 high-efficiency synchronous buck controller final information general description micrels mic2182 is a synchronous buck (step-down) switch- ing regulator controller. an all n-channel synchronous archi- tecture and powerful output drivers allow up to a 20a output current capabilty. the pwm and skip-mode control scheme allows efficiency to exceed 95% over a wide range of load current, making it ideal for battery powered applications, as well as high current distributed power supplies. the mic2182 operates from a 4.5v to 32v input and can operate with a maximum duty cycle of 86% for use in low- dropout conditions. it also features a shutdown mode that reduces quiescent current to 0.1 a. the mic2182 achieves high efficiency over a wide output current range by automatically switching between pwm and skip mode. skip-mode operation enables the converter to maintain high efficiency at light loads by turning off circuitry pertaining to pwm operation, reducing the no-load supply current from 1.6ma to 600 a. the operating mode is inter- nally selected according to the output load conditions. skip mode can be defeated by pulling the pwm pin low which reduces noise and rf interference. the mic2182 is available in a 16-pin sop (small-outline package) and ssop (shrink small-outline package) with an operating range from C40 c to +85 c. typical application vdd bst c6 0.1 f r1 2k r7 100k v in 4.5v to 30v* v out 3.3v/4a gnd c2 2.2nf c4 1nf c3 0.1 f c5 0.1 f c1 0.1 f c9 4.7 f 16v c11 22uf 35v x2 d2 sd103bws q2* si4884 d1 b140 c7 220uf 10v 2 l1 10 h r2 0.02 ? q1* si4884 hsd vsw lsd pgnd csh vout vref sgnd gnd mic2182-3.3bsm vin en/uvlo ss pwm comp sync c13, 1nf 10 6 2 1 3 5 4 7 9 8 12 13 15 16 14 11 * 30v maximum input voltage limit is due to standard 30v mosfet selection. see application information section for 5v to 3.3v/10a and other circuits. 4.5vC30v* to 3.3v/4a converter micrel, inc. ? 1849 fortune drive ? san jose, ca 95131 ? usa ? tel + 1 (408) 944-0800 ? fax + 1 (408) 944-0970 ? http://www.mic rel.com features ? 4.5v to 32v input voltage range ? 1.25v to 6v output voltage range ? 95% efficiency ? 300khz oscillator frequency ? current sense blanking ? 5 ? impedance mosfet drivers ? drives n-channel mosfets ? 600 a typical quiescent current (skip-mode) ? logic controlled micropower shutdown (i q < 0.1 a) ? current-mode control ? cycle-by-cycle current limiting ? built-in undervoltage protection ? adjustable undervoltage lockout ? easily synchronizable ? precision 1.245v reference output ? 0.6% total regulation ? 16-pin sop and ssop packages ? frequency foldback overcurrent protection ? sustained short-circuit protection at any input voltage ? 20a output current capability applications ? dc power distribution systems ? notebook and subnotebook computers ? pdas and mobile communicators ? wireless modems ? battery-operated equipment
mic2182 micrel mic2182 2 june 2000 ordering information part number voltage temperature range package mic2182bm adjustable C 40 c to +85 c 16-pin narrow sop mic2182-3.3bm 3.3v C 40 c to +85 c 16-pin narrow sop mic2182-5.0bm 5.0v C 40 c to +85 c 16-pin narrow sop mic2182bsm adjustable C 40 c to +85 c 16-pin narrow ssop mic2182-3.3bsm 3.3v C 40 c to +85 c 16-pin narrow ssop mic2182-5.0bsm 5.0v C 40 c to +85 c 16-pin narrow ssop pin configuration 1 2 3 4 16 15 14 13 hsd vsw bst lsd ss pwm comp sgnd mic2182 5 6 7 8 12 11 10 9 pgnd vdd vin vout sync en/uvlo fb csh adjustable 16-pin sop (m) 16-pin ssop (sm) 1 2 3 4 16 15 14 13 hsd vsw bst lsd ss pwm comp sgnd mic2182-x.x 5 6 7 8 12 11 10 9 pgnd vdd vin vout sync en/uvlo vref csh fixed 16-pin sop (m) 16-pin ssop (sm)
june 2000 3 mic2182 mic2182 micrel pin description pin number pin name pin function 1 ss soft-start (external component): connect external capacitor to ground to reduce inrush current by delaying and slowing the output voltage rise time. rise time is controlled by an internal 5 a current source that charges an external capacitor to v dd . 2 pwm pwm/skip-mode select (input): low sets pwm-mode operation. 1nf capacitor to ground sets automatic pwm/skip-mode selection. 3 comp compensation (output): internal error amplifier output. connect to capacitor or series rc network to compensate the regulator control loop. 4 sgnd small signal ground (return): route separately from other ground traces to the ( C ) terminal of c out . 5 sync frequency synchronization (input): optional. connect to external clock signal to synchronize the oscillator. leading edge of signal above the threshold terminates the switching cycle. connect to sgnd if unused. 6 en/uvlo enable/undervoltage lockout (input): low-level signal powers down the controller. input below the 2.5v threshold disables switching and functions as an accurate undervoltage lockout (uvlo). input below the threshold forces complete micropower (< 0.1 a) shutdown. 7 (fixed) vref reference voltage (output): 1.245v output. requires 0.1 f capacitor to ground. 7 (adj) fb feedback (input): regulates fb pin to 1.245v. see application information for resistor divider calculations. 8 csh current-sense high (input): current-limit comparator noninverting input. a built-in offset of 100mv between csh and v out pins in conjunction with the current-sense resistor set the current-limit threshold level. this is also the positive input to the current sense amplifier. 9 vout current-sense low (input): output voltage feedback input and inverting input for the current limit comparator and the current sense amplifier. 10 vin [battery] unregulated input (input): +4.5v to +32v supply input. 11 vdd 5v internal linear-regulator (output): v dd is the external mosfet gate drive supply voltage and an internal supply bus for the ic. bypass to sgnd with 4.7 f. v dd can supply up to 5ma for external loads. 12 pgnd mosfet driver power ground (return): connects to source of synchro- nous mosfet and the ( C ) terminal of c in 13 lsd low-side drive (output): high-current driver output for external synchronous mosfet. voltage swing is between ground and v dd . 14 bst boost (input): provides drive voltage for the high-side mosfet driver. the drive voltage is higher than the input voltage by v dd minus a diode drop. 15 vsw switch (return): high side mosfet driver return. 16 hsd high-side drive (output): high-current driver output for high-side mosfet. this node voltage swing is between ground and v in + 5v C v diode drop .
mic2182 micrel mic2182 4 june 2000 electrical characteristics v in = 15v; ss = open; v pwm = 0v; v shdn = 5v; i load = 0.1a; t a = 25 c, bold values indicate C 40 c t a +85 c; note 4 ; unless noted parameter condition min typ max units mic2182 [adjustable], (note 5) feedback voltage reference 1.233 1.245 1.257 v feedback voltage reference 1.220 1.245 1.270 v feedback voltage reference 4.5v < v in < 32v, 0 < v csh C v out < 75mv 1.208 1.245 1.282 v feedback bias current 10 na output voltage range 1.25 6 v output voltage line regulation v in = 4.5v to 32v, v csh C v out = 50mv 0.03 %/v output voltage load regulation 25mv < (v csh C v out ) < 75mv (pwm mode only) 0.5 % output voltage total regulation 0mv < (v csh C v out ) < 75mv (full load range) 4.5v < v in < 32v 0.6 % mic2182-3.3 output voltage 3.267 3.3 3.333 v output voltage 3.234 3.3 3.366 v output voltage 4.5v < v in < 32v, 0 < v csh C v out < 75mv 3.201 3.3 3.399 v output voltage line regulation v in = 4.5v to 32v, v csh C v out = 50mv 0.03 %/v output voltage load regulation 25mv < (v csh C v out ) < 75mv (pwm mode only) 0.5 % output voltage total regulation 0mv < (v csh C v out ) < 75mv (full load range) 4.5v < v in < 32v 0.8 % mic2182-5.0 output voltage 4.95 5.0 5.05 v output voltage 4.90 5.0 5.10 v output voltage 6.5v < v in < 32v, 0 < v csh C v out < 75mv 4.85 5.0 5.150 v output voltage line regulation v in = 6.5v to 32v, v csh C v out = 50mv 0.03 %/v output voltage load regulation 25mv < (v csh C v out ) < 75mv (pwm mode only) 0.5 % output voltage total regulation 0mv < (v csh C v out ) < 75mv (full load range) 6.5v < v in < 32v 0.8 % input and vdd supply pwm mode v pwm = 0v, excluding external mosfet gate drive current 1.6 2.5 ma skip mode i l = 0ma, v pwm floating (1nf capacitor to ground) 600 1500 a shutdown quiescent current v en/uvlo = 0v 0.1 5 a digital supply voltage (v dd )i l = 0ma to 5ma 4.7 5.3 v undervoltage lockout v dd upper threshold (turn on threshold) 4.2 v v dd lower threshold (turn off threshold) 4.1 v absolute maximum ratings (note 1) analog supply voltage (v in ) ....................................... +34v digital supply voltage (v dd ) ......................................... +7v driver supply voltage (b st ) .................................... v in +7v sense voltage (v out , c sh ) ............................. 7v to C 0.3v sync pin voltage (v sync ) ................................ 7v to C 0.3v enable pin voltage (v en/uvlo ) ...................................... v in power dissipation (p d ) sop ................................................ 400mw @ t a = 85 c ssop ............................................. 270mw @ t a = 85 c ambient storage temperature (t s ) ......... C 65 c to +150 c esd, note 3 operating ratings (note 2) analog supply voltage (v in ) ........................ +4.5v to +32v ambient temperature (t a ) ......................... C 40 c to +85 c junction temperature (t j ) ....................... C 40 c to +125 c package thermal resistance sop ( ja ) .......................................................... 100 c/w ssop ( ja ) ........................................................ 150 c/w
june 2000 5 mic2182 mic2182 micrel parameter condition min typ max units reference output (fixed versions only) reference voltage 1.220 1.245 1.270 v reference line regulation 6v < v in < 32v 1 mv reference load regulation 0 a < i ref < 100 a2mv enable/uvlo enable input threshold 0.6 1.1 1.6 v uvlo threshold 2.2 2.5 2.8 v enable input current v en/uvlo = 5v 0.1 5 a soft start soft-start current v ss = 0v C 3.5 C 5 C 6.5 a current limit current-limit threshold voltage v csh = v out 75 100 135 mv error amplifier error sense amplifier gain 20 current amp current sense amplifier gain 2.0 oscillator section oscillator frequency 270 300 330 khz maximum duty cycle 86 % minimum on-time v out = v out(nominal) + 200mv 140 250 ns sync threshold level 0.7 1.3 1.9 v sync input current v sync = 5v 0.1 5 a sync minimum pulse width 200 ns sync capture range note 6 330 khz frequency foldback threshold measured at vout pin 0.75 0.95 1.15 v foldback frequency 60 khz gate drivers rise/fall time c l = 3000pf 60 ns output driver impedance source 5 8.5 ? sink 3.5 6 ? driver nonoverlap time 80 ns pwm input pwm input current v pwm = 0v C 10 a note 1. exceeding the absolute maximum rating may damage the device. note 2. the device is not guaranteed to function outside its operating rating. note 3. devices are esd sensitive. handling precautions recommended. human body model, 1.5k in series with 100pf. note 4. 25 c limits are 100% production tested. limits over the operating temperature range are guaranteed by design and are not productio n tested. note 5. v in > 1.3 v out (for the feedback voltage reference and output voltage line and total regulation). note 6. see applications information for limitations on the maximum operating frequency.
mic2182 micrel mic2182 6 june 2000 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 -40 -20 0 20 40 60 80 100120140 current (ma) temperature ( c) quiescent current vs. temperature pwm skip 0 0.05 0.10 0.15 0.20 -40 -20 0 20 40 60 80 100120140 temperature ( c) -0.50 0 0.50 1.00 1.50 quiescent current vs. temperature uvlo mode (ma) shutdown ( quiescent current vs. supply voltage pwm skip -0.5 0 0.5 1.0 1.5 0 0.1 0.2 0.3 0.4 0.5 0 4 8 12 16 20 24 28 32 supply voltage (v) quiescent current vs. supply voltage uvlo mode (ma) shutdown ( a) current ( a) 1.236 1.238 1.240 1.242 1.244 1.246 1.248 1.250 1.252 1.254 1.256 0 4 8 121620242832 reference voltage (v) supply voltage (v) v ref (fixed versions) line regulation 1.200 1.210 1.220 1.230 1.240 1.250 1.260 0 200 400 600 800 1000 reference voltage (v) load current ( a) v ref (fixed versions) load regulation 1.240 1.245 1.250 1.255 1.260 -40 -20 0 20 40 60 80 100120140 reference voltage (v) temperature ( c) v ref (fixed versions) vs. temperature 4.0 4.2 4.4 4.6 4.8 5.0 0 4 8 121620242832 v dd regulator voltage (v) supply voltage (v) v dd line regulation 4.80 4.85 4.90 4.95 5.00 0 5 10 15 20 25 v dd regulator voltage (v) load current (ma) v dd load regulation 4.82 4.84 4.86 4.88 4.90 4.92 4.94 4.96 4.98 -40 -20 0 20 40 60 80 100120140 v dd regulator voltage (v) temperature ( c) v dd vs. temperature -10 -8 -6 -4 -2 0 2 4 6 8 10 -40 -20 0 20 40 60 80 100120140 frequency variation (%) temperature ( c) oscillator frequency vs. temperature typical characteristics -1.0 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1.0 0 4 8 121620242832 frequency variation (%) supply voltage (v) oscillator frequency vs. supply voltage
june 2000 7 mic2182 mic2182 micrel 4.0 4.2 4.4 4.6 4.8 5.0 -40 -20 0 20 40 60 80 100120140 current ( a) temperature ( c) soft-start current vs. temperature 0.08 0.09 0.10 0.11 0.12 -40 -20 0 20 40 60 80 100120140 overcurrent threshold (v) temperature ( c) overcurrent threshold vs. temperature 0 1 2 3 4 5 012345678 output voltage (v) output current (a) current-limit foldback v in = 5v v out = 3.3v r cs = 15m ?
mic2182 micrel mic2182 8 june 2000 block diagrams sgnd g m = 0.2 10 -3 low comp current limit skip-mode current limit pwm mode to skip mode hysteresis comp v bg 1.245v v bg 0.07v C 2%v bg error amp control logic v in v dd pwm pwm output corrective ramp reset reference oscillator 0.024v en/uvlo 6 11 14 10 16 15 13 12 8 9 7 4 1 2 5 3 ss pwm sync comp 100k mic2182 [adj.] fb r2 r1 vout csh vdd vbst c in vin hsd q2 q1 d1 d2 c bst c out v in v out l1 vsw lsd pgnd c comp r comp 4.7 f a v = 2 v 1.245v r1 r2 out =+ ? ? ? ? ? ? 1 v6v out(max) = . 0 current sense amp r cs figure 2a. adjustable output voltage version
june 2000 9 mic2182 mic2182 micrel low comp current limit skip-mode current limit hysteresis comp v bg 1.245v v bg 0.07v C 2%v bg error amp control logic v in v dd pwm pwm output corrective ramp reset reference oscillator 0.024v en/uvlo 6 11 14 10 16 15 13 12 8 9 4 7 1 2 5 3 ss pwm sync comp vref 100k g m = 0.2 10 -3 mic2182-x.x sgnd r2 50k r1* vout csh vdd vbst c in vin hsd q2 q1 d1 d2 c bst r cs c out v in v out l1 vsw lsd pgnd c comp r comp 4.7 f * 82.5k for 3.3v output 150k for 5v output a v = 2 current sense amp pwm mode to skip mode figure 2b. fixed output voltage versions
mic2182 micrel mic2182 10 june 2000 functional description see applications information following this section for com- ponent selection information and figure 14 and tables 1 through 5 for predesigned circuits. the mic2182 is a bicmos, switched-mode, synchronous step-down (buck) converter controller. current-mode control is used to achieve superior transient line and load regulation. an internal corrective ramp provides slope compensation for stable operation above a 50% duty cycle. the controller is optimized for high-efficiency, high-performance dc-dc con- verter applications. the mic2182 block diagrams are shown in figure 2a and figure 2b. the mic2182 controller is divided into 6 functions. ? control loop - pwm operation - skip-mode operation ? current limit ? reference, enable and uvlo ? mosfet gate drive ? oscillator and sync ? soft start control loop pwm and skip modes of operation the mic2182 operates in pwm (pulse-width-modulation) mode at heavier output load conditions. at lighter load condi- tions, the controller can be configured to automatically switch to a pulse-skipping mode to improve efficiency. the potential disadvantage of skip mode is the variable switching fre- quency that accompanies this mode of operation. the occur- rence of switching pulses depends on component values as well as line and load conditions. there is an external sync function that is disabled in skip mode. in pwm mode, the synchronous buck converter forces continuous current to flow in the inductor. in skip mode, current through the inductor can settle to zero, causing voltage ringing across the induc- tor. pulling the pwm pin (pin 2) low will force the controller to operate in pwm mode for all load conditions, which will improve cross regulation of transformer coupled, multiple output configurations. pwm control loop the mic2182 uses current-mode control to regulate the output voltage. this method senses the output voltage (outer loop) and the inductor current (inner loop). it uses inductor current and output voltage to determine the duty cycle of the buck converter. sampling the inductor current removes the inductor from the control loop, which simplifies compensa- tion. current sense amp v bg 1.245v v bg error amp v in v dd corrective ramp pwm comparator reset reference oscillator 11 14 10 16 15 13 12 8 9 7 3 comp 100k mic2182 [adj.] pwm mode fb r2 r1 vout csh vdd vbst c in vin hsd q2 q1 d1 d2 c bst c out v in v out l1 vsw lsd pgnd c comp r comp 4.7 f v 1.245v r1 r2 out =+ ? ? ? ? ? ? 1 s r q control logic and pulse-width modulator r cs g m = 0.2 10 -3 a v = 2 0.024v pwm mode to skip mode low forces skip mode figure 3. pwm operation
june 2000 11 mic2182 mic2182 micrel a block diagram of the mic2182 pwm current-mode control loop is shown in figure 3 and the pwm mode voltage and current waveforms are shown in figure 5a. the inductor current is sensed by measuring the voltage across the resistor, r cs . a ramp is added to the amplified current-sense signal to provide slope compensation, which is required to prevent unstable operation at duty cycles greater than 50%. a transconductance amplifier is used for the error amplifier, which compares an attenuated sample of the output voltage with a reference voltage. the output of the error amplifier is the comp (compensation) pin, which is compared to the current-sense waveform in the pwm block. when the current signal becomes greater than the error signal, the comparator turns off the high-side drive. the comp pin (pin 3) provides access to the output of the error amplifier and allows the use of external components to stabilize the voltage loop. skip-mode control loop this control method is used to improve efficiency at light output loads. at light output currents, the power drawn by the mic2182 is equal to the input voltage times the ic supply current (i q ). at light output currents, the power dissipated by the ic can be a significant portion of the total output power, which lowers the efficiency of the power supply. the mic2182 draws less supply current in skip mode by disabling portions of the control and drive circuitry when the ic in not switching. the disadvantage of this method is greater output voltage ripple and variable switching frequency. a block diagram of the mic2182 skip mode is shown in figure 4. skip mode voltage and current waveforms are shown in figure 5b. low comp skip-mode current limit v bg 1.245v v bg 0.07v low forces pwm mode C 2%v bg v in v dd reference 11 14 10 16 15 13 12 8 9 7 mic2182 [adj.] skip mode fb r2 r1 vout csh vdd vbst c in vin hsd q2 q1 d2 c bst c out v in v out l1 vsw lsd pgnd 4.7 f v 1.245v r1 r2 out =+ ? ? ? ? ? ? 1 current sense amp s r q control logic and skip-mode logic r cs a v = 2 one shot low-side driver one shot hysteresis comp 1% figure 4. skip-mode operation
mic2182 micrel mic2182 12 june 2000 a hysteretic comparator is used in place of the pwm error amplifier and a current-limit comparator senses the inductor current. a one-shot starts the switching cycle by momentarily turning on the low side mosfet to insure the high side drive boost capacitor, cbst, is fully charged. the high side mos- fet is turned on and current ramps up in the inductor, l1. the high side drive is turned off when either the peak voltage on the input of the current-sense comparator exceeds the threshold, typically 35mv, or the output voltage rises above the hysteretic threshold of the output voltage comparator. once the high side mosfet is turned off, the load current discharges the output capacitor, causing v out to fall. the cycle repeats when v out falls below the lower threshold, C 1%. the maximum peak inductor current depends on the skip- mode current-limit threshold and the value of the current- sense resistor, r cs . i 35mv r inductor(peak) sense = figure 6 shows the improvement in efficiency that skip mode makes when at lower output currents. 0 20 40 60 80 100 0.01 0.1 1 10 100 efficiency (%) output current (a) skip pwm figure 6. efficiency v dd 0v 0v 0v 0v 0a v dd v in + v dd v in v sw reset pulse v hsd v lsd i load i l1 figure 5a. pwm-mode timing 0v 0v 0v 0a v dd +1% C 1% v nominal v in v out v sw v lsd v hsd v one-shot 0v v dd 0v v dd i lim(skip) i l1 v out i out 0a figure 5b. skip-mode timing
june 2000 13 mic2182 mic2182 micrel switching from pwm to skip mode the current sense amplifier in figure 3 monitors the average voltage across the current-sense resistor. the controller will switch from pwm to skip mode when the average voltage across the current-sense resistor drops below approximately 12mv. this is shown in figure 7b. the average output current at this transition level for is calculated below. i 0.012 r out(skipmode) cs = where: 0.012 = threshold voltage of the internal comparator r cs = current-sense resistor value switching from skip to pwm mode the frequency of occurrence of the skip-mode current pulses increase as the output current increases until the hysteretic duty cycle reaches 100% (continuous pulses). increasing the current past this point will cause the output voltage will drop. the low limit comparator senses the output voltage when it drops below 2% of the set output and automatically switches the converter to pwm mode. the inductor current in skip mode is a triangular wave shape a minimum value of 0 and a maximum value of 35mv/r cs (see figure 7b). the maximum average output current in skip mode is the average value of the inductor waveform: i 0.5 35mv r out(max skipmode) cs = the capacitor on the pwm pin (pin 2) is discharged when the ic transitions from skip to pwm mode. this forces the ic to remain in pwm mode for a fixed period of time. the added delay prevents unwanted switching between pwm and skip mode. the capacitor is charged with a 10ua current source on pin 2. the threshold on pin 2 is 2.5v. the delay for a typical 1nf capacitor is: t cv i 1nf 2.5v 10 a 250 s delay pwm threshold source = = = where: c pwm = capacitor connected to pin 2 current limit the current-limit circuit operates during pwm mode. the output current is detected by the voltage drop across the external current-sense resistor (r cs in figure 2.). the cur- rent-limit threshold is 100mv+35mv C 25mv. the current- sense resistor must be sized using the minimum current-limit threshold. the external components must be designed to withstand the maximum current limit. the current-sense resistor value is calculated by the equation below: r 75mv i cs out(max) = the maximum output current is: i 135mv r out(max) cs = the current-sense pins csh (pin 8) and v out (pin 9) are noise sensitive due to the low signal level and high input impedance. the pcb traces should be short and routed close to each other. a small (1nf to 0.1 f) capacitor across the pins will attenuate high frequency switching noise. when the peak inductor current exceeds the current-limit threshold, the current-limit comparator, in figure 2, turns off the high-side mosfet for the remainder of the cycle. the output voltage drops as additional load current is pulled from the converter. when the output voltage reaches approxi- mately 0.95v, the circuit enters frequency-foldback mode and the oscillator frequency will drop to 60khz while maintain- ing the peak inductor current equal to the nominal 100mv across the external current-sense resistor. this limits the maximum output power delivered to the load under a short circuit condition. reference, enable and, uvlo circuits the output drivers are enabled when the following conditions are satisfied: ? the v dd voltage (pin 11) is greater than its undervoltage threshold (typically 4.2v). ? the voltage on the enable pin is greater than the enable uvlo threshold (typically 2.5v) the internal bias circuit generates a 1.245v bandgap refer- ence voltage for the voltage error amplifier and a 5v v dd voltage for the gate drive circuit. the reference voltage in the fixed-output-voltage versions of the mic2182 is buffered and brought to pin 7. the v ref pin should be bypassed to gnd (pin 4) with a 0.1 f capacitor. the adjustable version of the mic2182 uses pin 7 for output voltage sensing. a decoupling capacitor on pin 7 is not used in the adjustable output voltage version. 0a i lim(skip) inductor current 35mv threshold across r cs . figure 7a. maximum skip-mode-load inductor current 0a i min(pwm) inductor current 12mv threshold of average voltage across r cs . figure 7b. minimum pwm-mode-load inductor current for pwm operation
mic2182 micrel mic2182 14 june 2000 the enable pin (pin 6) has two threshold levels, allowing the mic2182 to shut down in a low current mode, or turn off output switching in uvlo mode. an enable pin voltage lower than the shutdown threshold turns off all the internal circuitry and reduces the input current to typically 0.1 a. if the enable pin voltage is between the shutdown and uvlo thresholds, the internal bias, v dd , and reference voltages are turned on. the soft-start pin is forced low by an internal discharge mosfet. the output drivers are inhibited from switching and remain in a low state. raising the enable voltage above the uvlo threshold of 2.5v allows the soft- start capacitor to charge and enables the output drivers. either of two uvlo conditions will pull the soft-start capacitor low. ? when the v dd drops below 4.1v ? when the enable pin drops below the 2.5v threshold mosfet gate drive the mic2182 high-side drive circuit is designed to switch an n-channel mosfet. referring to the block diagram in figure 2, a bootstrap circuit, consisting of d2 and c bst , supplies energy to the high-side drive circuit. capacitor c bst is charged while the low-side mosfet is on and the voltage on the v sw pin (pin 15) is approximately 0v. when the high-side mosfet driver is turned on, energy from c bst is used to turn the mosfet on. as the mosfet turns on, the voltage on the v sw pin increases to approximately v in . diode d2 is re- versed biased and c bst floats high while continuing to keep the high-side mosfet on. when the low-side switch is turned back on, c bst is recharged through d2. the drive voltage is derived from the internal 5v v dd bias supply. the nominal low-side gate drive voltage is 5v and the nominal high-side gate drive voltage is approximately 4.5v due the voltage drop across d2. a fixed 80ns delay between the high- and low-side driver transitions is used to prevent current from simultaneously flowing unimpeded through both mosfets. oscillator and sync the internal oscillator is free running and requires no external components. the nominal oscillator frequency is 300khz. if the output voltage is below approximately 0.95v, the oscilla- tor operates in a frequency-foldback mode and the switching frequency is reduced to 60khz. the sync input (pin 5) allows the mic2182 to synchronize with an external clock signal. the rising edge of the sync signal generates a reset signal in the oscillator, which turns off the low-side gate drive output. the high-side drive then turns on, restarting the switching cycle. the sync signal is inhibited when the controller operates in skip mode or during frequency foldback. the sync signal frequency must be greater than the maximum specified free running frequency of the mic2182. if the synchronizing frequency is lower, double pulsing of the gate drive outputs will occur. when not used, the sync pin must be connected to ground. figure 8 shows the timing between the external sync signal (trace 2), the low-side drive (trace 1) and the high-side drive (trace r1). there is a delay of approximately 250ns between the rising edge of the external sync signal and turnoff of the low-side mosfet gate drive. some concerns of operating at higher frequencies are: ? higher power dissipation in the internal v dd regulator. this occurs because the mosfet gates require charge to turn on the device. the average current required by the mosfet gate increases with switching frequency. this in- creases the power dissipated by the internal v dd regulator. figure 10 shows the total gate charge which can be driven by the mic2182 over the input voltage range, for different values of switching frequency. the total gate charge includes both the high- and low-side mosfets. the larger sop package is capable of dissipat- ing more power than the ssop package and can drive larger mosfets with higher gate drive requirements. time sync signal low-side drive high-side drive figure 8. sync waveforms time v ss v out figure 9. startup waveforms
june 2000 15 mic2182 mic2182 micrel ? reduced maximum duty cycle due to switching transition times and constant delay times in the controller. as the switching frequency increased, the switching period decreases. the switching transition times and constant delays in the mic2182 start to become noticeable. the effect is to reduce the maximum duty cycle of the controller. this will cause the minimum input to output differential voltage (dropout voltage) to increase. 0 20 40 60 80 100 0 4 8 12 16 20 24 28 32 gate charge (nc) supply voltage (v) 400khz 300khz 500khz sop figure 10a. sop gate charge vs. input voltage 0 20 40 60 80 100 0 4 8 121620242832 gate charge (nc) supply voltage (v) ssop 400khz 300khz 500khz figure 10b. ssop gate charge vs. input voltage it is recommended that the user limits the maximum synchro- nized frequency to 600khz. if a higher synchronized fre- quency is required, it may be possible and will be design dependent. please consult micrel applications for assis- tance. soft start soft start reduces the power supply input surge current at startup by controlling the output voltage rise time. the input surge appears while the output capacitance is charged up. a slower output rise time will draw a lower input surge current. soft start may also be used for power supply sequencing. the soft-start voltage is applied directly to the pwm compara- tor. a 5ua internal current source is used to charge up the soft-start capacitor. the capacitor is discharged when either the enable voltage drops below the uvlo threshold (2.5v) or the v dd voltage drops below the uvlo level (4.1v). the part switches at a minimum duty cycle when the soft-start pin voltage is less than 0.4v. this maintains a charge on the bootstrap capacitor and insures high-side gate drive voltage. as the soft-start voltage rises above 0.4v, the duty cycle increases from the minimum duty cycle to the operating duty cycle. the oscillator runs at the foldback frequency of 60khz until the output voltage rises above 0.95v. above 0.95v, the switching frequency increases to 300khz (or the sync d frequency), causing the output voltage to rise a greater rate. the rise time of the output is dependent on the soft-start capacitor, output capacitance, output voltage, and load cur- rent. the oscilloscope photo in figure 9 show the output voltage and the soft-start pin voltage at startup. minimum pulse width the mic2182 has a specified minimum pulse width. this minimum pulse width places a lower limit on the minimum duty cycle of the buck converter. when the mic2182 is operating in forced pwm mode (pin 2 low) and when the output current is very low or zero, there is a limit on the ratio of v out /v in . if this limit is exceeded, the output voltage will rise above the regulated voltage level. a minimum load is required to prevent the output from rising up. this will not occur for output voltages greater than 3v. figure 11 should be used as a guide when the mic2182 is forced into pwm-only mode. the actual maximum input voltage will depend on the exact external components used (mosfets, inductors, etc.). 10 15 20 25 30 35 0123456 input voltage (v) output voltage (v) figure 11. max. input voltage in forced-pwm mode this restriction does not occur when the mic2182 is set to automatic mode (pin 2 connected to a capacitor) since the converter operates in skip mode at low output current.
mic2182 micrel mic2182 16 june 2000 applications information the following applications information includes component selection and design guidelines. see figure 14 and tables 1 through 5 for predesigned circuits. inductor selection values for inductance, peak, and rms currents are required to select the output inductor. the input and output voltages and the inductance value determine the peak to peak inductor ripple current. generally, higher inductance values are used with higher input voltages. larger peak to peak ripple currents will increase the power dissipation in the inductor and mosfets. larger output ripple currents will also require more output capacitance to smooth out the larger ripple current. smaller peak to peak ripple currents require a larger inductance value and therefore a larger and more expensive inductor. a good compromise between size, loss and cost is to set the inductor ripple current to be equal to 20% of the maximum output current. the inductance value is calculated by the equation below. l v(v v) v f 0.2 i out in(max) out in(max) s out(max) = ? where: f s = switching frequency 0.2 = ratio of ac ripple current to dc output current v in(max) = maximum input voltage the peak-to-peak inductor current (ac ripple current) is: i v(v v) vfl pp out in(max) out in(max) s = ? the peak inductor current is equal to the average output current plus one half of the peak to peak inductor ripple current. i i 0.5 i pk out(max) pp =+ the rms inductor current is used to calculate the i 2 r losses in the inductor. i (rms) i 1 1 3 i i inductor out(max) pp out(max) 2 =+ ? ? ? ? ? ? maximizing efficiency requires the proper selection of core material and minimizing the winding resistance. the high frequency operation of the mic2182 requires the use of ferrite materials for all but the most cost sensitive applications. lower cost iron powder cores may be used but the increase in core loss will reduce the efficiency of the power supply. this is especially noticeable at low output power. the winding resistance decreases efficiency at the higher output current levels. the winding resistance must be minimized although this usually comes at the expense of a larger inductor. the power dissipated in the inductor is equal to the sum of the core and copper losses. at higher output loads, the core losses are usually insignificant and can be ignored. at lower output currents, the core losses can be a significant contribu- tor. core loss information is usually available from the mag- netics vendor. copper loss in the inductor is calculated by the equation below: p i (rms) r inductor cu inductor 2 winding = the resistance of the copper wire, r winding , increases with temperature. the value of the winding resistance used should be at the operating temperature. r r 1 0.0042 (t t ) winding(hot) winding(20 c) hot 20 c =+? () where: t hot = temperature of the wire under operating load t 20 c = ambient temperature r winding(20 c) is room temperature winding resistance (usually specified by the manufacturer) current-sense resistor selection low inductance power resistors, such as metal film resistors should be used. most resistor manufacturers make low inductance resistors with low temperature coefficients, de- signed specifically for current-sense applications. both resis- tance and power dissipation must be calculated before the resistor is selected. the value of r sense is chosen based on the maximum output current and the maximum threshold level. the power dissipated is based on the maximum peak output current at the minimum overcurrent threshold limit. r 75mv i sense out(max) = the maximum overcurrent threshold is: i 135mv r overcurrent(max) cs = = mosfet selection external n-channel logic-level power mosfets must be used for the high- and low-side switches. the mosfet gate- to-source drive voltage of the mic2182 is regulated by an internal 5v v dd regulator. logic-level mosfets, whose operation is specified at v gs = 4.5v must be used. it is important to note the on-resistance of a mosfet increases with increasing temperature. a 75 c rise in junc- tion temperature will increase the channel resistance of the mosfet by 50% to 75% of the resistance specified at 25 c. this change in resistance must be accounted for when calculating mosfet power dissipation. total gate charge is the charge required to turn the mosfet on and off under specified operating conditions (v ds and v gs ). the gate charge is supplied by the mic2182 gate drive circuit. at 300khz switching frequency and above, the gate
june 2000 17 mic2182 mic2182 micrel charge can be a significant source of power dissipation in the mic2182. at low output load this power dissipation is notice- able as a reduction in efficiency. the average current re- quired to drive the high-side mosfet is: iqf g[high-side](avg) g s = where: i g[high-side](avg) = average high-side mosfet gate current q g = total gate charge for the high-side mosfet taken from manufacturer s data sheet with v gs = 5v. the low-side mosfet is turned on and off at v ds = 0 because the freewheeling diode is conducting during this time. the switching losses for the low-side mosfet is usually negligable. also, the gate drive current for the low- side mosfet is more accurately calculated using c iss at v ds = 0 instead of gate charge. for the low-side mosfet: icvf g[low-side](avg) iss gs s = since the current from the gate drive comes from the input voltage, the power dissipated in the mic2182 due to gate drive is: pvi i gate drive in g[high-side](avg) g[low-side](avg) =+ () a convenient figure of merit for switching mosfets is the on- resistance times the total gate charge (r ds(on) q g ). lower numbers translate into higher efficiency. low gate-charge logic-level mosfets are a good choice for use with the mic2182. power dissipation in the mic2182 package limits the maximum gate drive current. refer to figure 10 for the mic2182 gate drive limits. parameters that are important to mosfet switch selection are: ? voltage rating ? on-resistance ? total gate charge the voltage rating of the mosfets are essentially equal to the input voltage. a safety factor of 20% should be added to the v ds(max) of the mosfets to account for voltage spikes due to circuit parasitics. the power dissipated in the switching transistor is the sum of the conduction losses during the on-time (p conduction ) and the switching losses that occur during the period of time when the mosfets turn on and off (p ac ). pp p sw conduction ac =+ where: p i (rms) r conduction sw 2 sw = pp p ac ac(off) ac(on) =+ r sw = on-resistance of the mosfet switch. making the assumption the turn-on and turnoff transition times are equal, the transition time can be approximated by: t cvc v i t iss gs oss in g = + where: c iss and c oss are measured at v ds = 0. i g = gate drive current (1a for the mic2182) the total high-side mosfet switching loss is: p(vv)itf ac in d pk t s =+ where: t t = switching transition time (typically 20ns to 50ns) v d = freewheeling diode drop, typically 0.5v. f s it the switching frequency, nominally 300khz the low-side mosfet switching losses are negligible and can be ignored for these calculations. rms current and mosfet power dissipation calculation under normal operation, the high-side mosfet s rms current is greatest when v in is low (maximum duty cycle). the low-side mosfet s rms current is greatest when v in is high (minimum duty cycle). however, the maximum stress the mosfets see occurs during short circuit conditions, where the output current is equal to i overcurrent(max) . (see the sense resistor section). the calculations below are for normal operation. to calculate the stress under short circuit condi- tions, substitute i overcurrent(max) for i out(max) . use the formula below to calculate d under short circuit conditions. d 0.063 1.8 10 v short circuit 3 in =? ? the rms value of the high-side switch current is: i (rms) d i i 12 sw(highside) out(max) 2 pp 2 = + ? ? ? ? ? ? i (rms) 1 d i i 12 sw(low side) out(max) 2 pp 2 =? () + ? ? ? ? ? ? where: d = duty cycle of the converter d v v out in = = efficiency of the converter. converter efficiency depends on component parameters, which have not yet been selected. for design purposes, an efficiency of 90% can be used for v in less than 10v and 85% can be used for v in greater than 10v. the efficiency can be more accurately calculated once the design is complete. if the assumed efficiency is grossly inaccurate, a second iteration through the design procedure can be made. for the high-side switch, the maximum dc power dissipation is: p r i (rms) switch1(dc) ds(on)1 sw1 2 =
mic2182 micrel mic2182 18 june 2000 for the low-side switch (n-channel mosfet), the dc power dissipation is: p r i (rms) switch2(dc) ds(on)2 sw 2 2 = since the ac switching losses for the low side mosfet is near zero, the total power dissipation is: pp low-side mosfet(max) switch2(dc) = the total power dissipation for the high side mosfet is: ppp highsidemosfet(max) switch 1(dc) ac =+ external schottky diode an external freewheeling diode is used to keep the inductor current flow continuous while both mosfets are turned off. this dead time prevents current from flowing unimpeded through both mosfets and is typically 80ns the diode conducts twice during each switching cycle. although the average current through this diode is small, the diode must be able to handle the peak current. i i 2 80ns f d(avg) out s = the reverse voltage requirement of the diode is: v (rrm) v diode in = the power dissipated by the schottky diode is: pi v diode d(avg) f = where: v f = forward voltage at the peak diode current the external schottky diode, d2, is not necessary for circuit operation since the low-side mosfet contains a parasitic body diode. the external diode will improve efficiency and decrease high frequency noise. if the mosfet body diode is used, it must be rated to handle the peak and average current. the body diode has a relatively slow reverse recovery time and a relatively high forward voltage drop. the power lost in the diode is proportional to the forward voltage drop of the diode. as the high-side mosfet starts to turn on, the body diode becomes a short circuit for the reverse recovery period, dissipating additional power. the diode recovery and the circuit inductance will cause ringing during the high-side mosfet turn-on. an external schottky diode conducts at a lower forward voltage preventing the body diode in the mosfet from turning on. the lower forward voltage drop dissipates less power than the body diode. the lack of a reverse recovery mechanism in a schottky diode causes less ringing and less power loss. depending on the circuit components and oper- ating conditions, an external schottky diode will give a 1/2% to 1% improvement in efficiency. figure 12 illustrates the difference in noise on the vsw pin with and without a schottky diode. output capacitor selection the output capacitor values are usually determined by the capacitors esr (equivalent series resistance). voltage rating and rms current capability are two other important factors in selecting the output capacitor. recommended capacitors are tantalum, low-esr aluminum electrolytics, and os-con. the output capacitor s esr is usually the main cause of output ripple. the maximum value of esr is calculated by: r v i esr out pp ? where: v out = peak to peak output voltage ripple i pp = peak to peak inductor ripple current the total output ripple is a combination of the esr and the output capacitance. the total ripple is calculated below: ? v i(1d) cf ir out pp out s 2 pp esr 2 = ? ? ? ? ? ? ? + () where: d = duty cycle c out = output capacitance value f s = switching frequency the voltage rating of capacitor should be twice the output voltage for a tantalum and 20% greater for an aluminum electrolytic or os-con. the output capacitor rms current is calculated below: i (rms) i 12 c pp out = the power dissipated in the output capacitor is: p i (rms) r diss(c c 2 esr(c ) out out out ) = input capacitor selection the input capacitor should be selected for ripple current rating and voltage rating. tantalum input capacitors may fail when subjected to high inrush currents, caused by turning the input supply on. tantalum input capacitor voltage rating should be at least 2 times the maximum input voltage to maximize reliability. aluminum electrolytic, os-con, and multilayer polymer film capacitors can handle the higher inrush currents without voltage derating. time with freewheeling diode without freewheeling diode figure 12. switch output noise with and without shottky diode
june 2000 19 mic2182 mic2182 micrel the input voltage ripple will primarily depend on the input capacitors esr. the peak input current is equal to the peak inductor current, so: ? vi r in inductor(peak) esr(c ) in = the input capacitor must be rated for the input current ripple. the rms value of input capacitor current is determined at the maximum output current. assuming the peak to peak induc- tor ripple current is low: i (rms) i d (1 d) c out(max) in ?? the power dissipated in the input capacitor is: p i (rms) r diss(c ) c 2 esr(c ) in in in = voltage setting components the mic2182-3.3 and mic2182-5.0 ics contain internal voltage dividers that set the output voltage. the mic2182 adjustable version requires two resistors to set the output voltage as shown in figure 13. error amp 7 mic2182 [adj.] fb v ref 1.245v r2 r1 figure 13. voltage-divider configuration the output voltage is determined by the equation: vv 1 r1 r2 o ref =+ ? ? ? ? ? ? where: v ref for the mic2182 is typically 1.245v. a typical value of r1 can be between 3k and 10k. if r1 is too large it may allow noise to be introduced into the voltage feedback loop. if r1 is too small in value it will decrease the efficiency of the power supply, especially at low output loads. once r1 is selected, r2 can be calculated using: r2 vr1 vv ref o ref = ? voltage divider power dissipation the reference voltage and r2 set the current through the voltage divider. i v r2 divider ref = the power dissipated by the divider resistors is: p (r1 r2) i divider divider 2 =+ efficiency calculation and considerations efficiency is the ratio of output power to input power. the difference is dissipated as heat in the buck converter. under light output load, the significant contributors are: ? supply current to the mic2182 ? mosfet gate-charge power (included in the ic supply current) ? core losses in the output inductor to maximize efficiency at light loads: ? use a low gate-charge mosfet or use the smallest mosfet, which is still adequate for maximum output current. ? allow the mic2182 to run in skip mode at lower currents. ? use a ferrite material for the inductor core, which has less core loss than an mpp or iron power core. under heavy output loads the significant contributors to power loss are (in approximate order of magnitude): ? resistive on-time losses in the mosfets ? switching transition losses in the mosfets ? inductor resistive losses ? current-sense resistor losses ? input capacitor resistive losses (due to the capacitors esr) to minimize power loss under heavy loads: ? use logic-level, low on-resistance mosfets. multiplying the gate charge by the on-resistance gives a figure of merit, providing a good bal- ance between low and high load efficiency. ? slow transition times and oscillations on the voltage and current waveforms dissipate more power during turn-on and turnoff of the mosfets. a clean layout will minimize parasitic inductance and capacitance in the gate drive and high current paths. this will allow the fastest transition times and waveforms without oscilla- tions. low gate-charge mosfets will transition faster than those with higher gate-charge requirements. ? for the same size inductor, a lower value will have fewer turns and therefore, lower winding resistance. however, using too small of a value will require more output capacitors to filter the output ripple, which will force a smaller band- width, slower transient response and possible instability under certain conditions. ? lowering the current-sense resistor value will decrease the power dissipated in the resistor. however, it will also increase the overcurrent limit and will require larger mosfets and inductor components. ? use low-esr input capacitors to minimize the power dissipated in the capacitors esr. decoupling capacitor selection the 4.7 f decoupling capacitor is used to minimize noise on the vdd pin. the placement of this capacitor is critical to the proper operation of the ic. it must be placed right next to the
mic2182 micrel mic2182 20 june 2000 pins and routed with a wide trace. the capacitor should be a good quality tantalum. an additional 1 f ceramic capacitor may be necessary when driving large mosfets with high gate capacitance. incorrect placement of the v dd decoupling capacitor will cause jitter or oscillations in the switching waveform and large variations in the overcurrent limit. a 0.1 f ceramic capacitor is required to decouple the vin. the capacitor should be placed near the ic and connected directly to between pin 10 (vcc) and pin 12 (pgnd). pcb layout and checklist pcb layout is critical to achieve reliable, stable and efficient performance. a ground plane is required to control emi and minimize the inductance in power, signal and return paths. the following guidelines should be followed to insure proper operation of the circuit. ? signal and power grounds should be kept separate and connected at only one location. large currents or high di/dt signals that occur when the mosfets turn on and off must be kept away from the small signal connections. ? the connection between the current-sense resistor and the mic2182 current-sense inputs (pin 8 and 9) should have separate traces, routed from the terminals directly to the ic pins. the traces should be routed as closely as possible to each other and their length should be minimized. avoid running the traces under the inductor and other switching components. a 1nf to 0.1 f capacitor placed between pins 8 and 9 will help attenuate switching noise on the current sense traces. this capacitor should be placed close to pins 8 and 9. ? when the high-side mosfet is switched on, the critical flow of current is from the input capacitor through the mosfet, inductor, sense resistor, output capacitor, and back to the input capacitor. these paths must be made with short, wide pieces of trace. it is good practice to locate the ground terminals of the input and output capaci- tors close to each. ? when the low-side mosfet is switched on, current flows through the inductor, sense resistor, output capacitor, and mosfet. the source of the low-side mosfet should be located close to the output capacitor. ? the freewheeling diode, d1 in figure 2, con- ducts current during the dead time, when both mosfets are off. the anode of the diode should be located close to the output capacitor ground terminal and the cathode should be located close to the input side of the inductor. ? the 4.7 f capacitor, which connects to the vdd terminal (pin 11) must be located right at the ic. the vdd terminal is very noise sensitive and placement of this capacitor is very critical. connections must be made with wide trace. the capacitor may be located on the bottom layer of the board and connected to the ic with multiple vias. ? the v in bypass capacitor should be located close to the ic and connected between pins 10 and 12. connections should be made with a ground and power plane or with short, wide trace.
june 2000 21 mic2182 mic2182 micrel vdd bst c6 0.1 f r1 2k r7 100k v in v out gnd c2 2.2nf c4 1nf c3 0.1 f c5 0.1 f c1 0.1 f 50v c9 4.7 f 16v c11 (table) d2 sd103bws q2 (table) d1 (table) c7 (table) c12 0.1 f 50v l1 (table) r2 (table) q1 (table) hsd vsw lsd pgnd csh vout vref sgnd gnd mic2182 vin en/uvlo ss pwm comp sync c13, 1nf figure 14. basic circuit diagram for use with tables 3 through 6 n o i t a c i f i c e p st i m i l e l p p i r y c n e u q e r f g n i h c t i w se g a t l o v t u p t u o f o % 1 e r u t a r e p m e t t n e i b m a m u m i x a m5 8 c y t i l i b a p a c t i u c r i c - t r o h ss u o u n i t n o c y c n e u q e r f g n i h c t i w sz h k 0 0 3 table 1. specifications for figure 14 and tables 3 through 6 manufacturer telephone number (usa) web address avx (803) 946-0690 www.avxcorp.com central semiconductor (516) 435-1110 www.centralsemi.com coiltronics (561) 241-7876 www.coiltronics.com irc (704) 264-8861 ir (310) 322-3331 www.irf.com micrel (408) 944-0800 www.micrel.com vishay/lite on (805) 446-4800 www.vishay-liteon.com (diodes) vishay/siliconix (800) 554-5665 www.siliconix.com (mosfets) vishay/dale (800) 487-9437 www.vishaytechno.com (inductors and resistors) sumida (847) 956-0666 www.japanlink.com/sumida table 2. component suppliers predesigned circuits a single schematic diagram, shown in figure 14, can be used to build power supplies ranging from 3a to 10a at the common output voltages of 1.8v, 2.5v, 3.3v, and 5v. components that vary, depending upon output current and voltage, are listed in the accompanying tables 3 through 6. power supplies larger than 10a can also be constructed using the mic2182 using larger power-handling compo- nents. the power supply operating characteristics graphs follow- ing the component and vendor tables provide useful informa- tion about the actual performance of some of these circuits.
mic2182 micrel mic2182 22 june 2000 3a (6.5v C 30v) 4a (6.5v C 30v) 5a (6.5v C 30v) 10a (6.5v C 10v) reference part no. / description part no. / description part no. / description part no. / description c7 qty: 2 qty: 2 qty: 2 qty: 2 tpse227m010r0100 tpse227m010r0100 tpsv227m010r0060 tpsv337m010r0060 avx, 220 f 10v, avx, 220 f 10v, avx, 220 f 10v, avx, 330 f 10v, 0.1 ? esr, 0.1 ? esr, 0.06 ? esr, 0.06 ? esr, output filter capacitor output filter capacitor output filter capacitor output filter capacitor c11 qty: 2 qty: 3 qty: 4 qty: 4 tpse226m035r0300 tpse226m035r0300 tpse226m035r0300 tpsv107m020r0085 avx, 22 f 35v, avx, 22 f 35v, avx, 22 f 35v, avx, 100 f 20v, 0.3 ? esr, 0.3 ? esr, 0.3 ? esr, 0.06 ? esr, input filter capacitor input filter capacitor input filter capacitor input filter capacitor d1 qty: 1 b140, vishay, qty: 1 b140, vishay, qty: 1 b140, vishay, qty: 1 b330, vishay, freewheeling diode freewheeling diode freewheeling diode freewheeling diode l1 qty: 1 cdrh125-100, qty: 1 cdrh127-100, qty: 1 cdrh127-100 qty: 1 up4b-3r3, sumida inductor, sumida inductor, sumida, coiltronics, 10 h 4a, 10 h 5a, 10 h 5a, 3.3 h 11a, output inductor output inductor output inductor output inductor q1 qty: 1 si4800, siliconix, qty: 1 si4800, siliconix, qty: 1 si4884, siliconix, qty: 2 si4884, siliconix low-side mosfet low-side mosfet low-side mosfet low-side mosfet q2 qty: 1 si4800, siliconix, qty: 1 si4800, siliconix, qty: 1 si4884, siliconix, qty: 2 si4884, siliconix, high-side mosfet high-side mosfet high-side mosfet high-side mosfet r2 qty: 1 qty: 1 qty: 1 qty: 2 wsl-2010 .025 1%, wsl-2010 .020 1%, wsl-2512 .015 1%, wsl-2512 .015 1% , vishay, 0.025, 1%, 0.5w, vishay, 0.02, 1%, 0.5w, vishay, 0.015, 1%, 1w, vishay, 0.015, 1%, 1w, current sense resistor current sense resistor current sense resistor current sense resistor u1 mic2182-5.0bsm or mic2182-5.0bsm or mic2182-5.0bsm or mic2182-5.0bm mic2182-5.0bm mic2182-5.0bm mic2182-5.0bm table 3. components for 5v output 3a (4.5v C 30v) 4a (4.5v C 30v) 5a (4.5v C 30v) 10a (4.5v C 5.5v) reference part no. / description part no. / description part no. / description part no. / description c7 qty: 2 qty: 2 qty: 2 qty: 2 tpse227m010r0100 tpse227m010r0100 tpsv227m010r0060 tpsv477m006r0055 avx, 220 f 10v, avx, 220 f 10v, avx, 220 f 10v, avx, 470 f 6.3v, 0.1 ? esr, 0.1 ? esr, 0.06 ? esr, 0.055 ? esr, output filter capacitor output filter capacitor output filter capacitor output filter capacitor c11 qty: 2 qty: 2 qty: 3 qty: 3 tpse226m035r0300 tpse226m035r0300 tpse226m035r0300 tpsv227m016r0075 avx, 22 f 35v, avx, 22 f 35v, avx, 22 f 35v, avx, 220 f 16v, 0.3 ? esr, 0.3 ? esr, 0.3 ? esr, 0.075 ? esr, input filter capacitor input filter capacitor input filter capacitor filter capacitor d1 qty: 1 b140, vishay, qty: 1 b140, vishay, qty: 1 b140, vishay, qty: 1 b330, vishay, freewheeling diode freewheeling diode freewheeling diode freewheeling diode l1 qty: 1 cdrh125-100, qty: 1 cdrh127-100, qty: 1 cdrh127-100 qty: 1 up4b-3r3, sumida inductor, sumida inductor, sumida, coiltronics, 10 h 4a, 10 h 5a, 10 h 5a, 3.3 h 11a, output inductor output inductor output inductor output inductor q1 qty: 1 si4800, siliconix, qty: 1 si4800, siliconix, qty: 1 si4800, siliconix, qty: 2 si4884, siliconix, low-side mosfet low-side mosfet low-side mosfet low-side mosfet q2 qty: 1 si4800, siliconix, qty: 1 si4800, siliconix, qty: 1 si4884, siliconix, qty: 2 si4884, siliconix, high-side mosfet high-side mosfet high-side mosfet high-side mosfet r2 qty: 1 qty: 1 qty: 1 qty: 2 wsl-2010 .025 1%, wsl-2010 .020 1%, wsl-2512 .015 1%, wsl-2512 .015 1% , vishay, 0.025, 1%, 0.5w, vishay, 0.02, 1%, 0.5w, vishay, 0.015, 1%, 1w, vishay, 0.015, 1%, 1w, current sense resistor current sense resistor current sense resistor current sense resistor u1 mic2182-3.3bsm or mic2182-3.3bm or mic2182-3.3bm or mic2182-3.3bm mic2182-3.3bm mic2182-3.3bsm mic2182-3.3bsm table 4. components for 3.3v output
june 2000 23 mic2182 mic2182 micrel 3a (4.5v C 30v) 4a (4.5v C 30v) 5a (4.5v C 30v) 10a (4.5v C 5.5v) reference part no. / description part no. / description part no. / description part no. / description c7 qty: 2 qty: 2 qty: 2 qty: 2 tpse227m010r0100 tpse227m010r0100 tpsv227m010r0060 tpsv447m006r0055 avx, 220 f 10v, avx, 220 f 10v, avx, 220 f 10v, avx, 470 f 6.3v, 0.1 ? esr, 0.1 ? esr, 0.06 ? esr, 0.06 ? esr, output filter capacitor output filter capacitor output filter capacitor output filter capacitor c11 qty: 2 qty: 2 qty: 2 qty: 3 tpse226m035r0300 tpse226m035r0300 tpse226m035r0300 tpsv227m016r0075 avx, 22 f 35v, avx, 22 f 35v, avx, 22 f 35v, avx, 220 f 16v, 0.3 ? esr, 0.3 ? esr, 0.3 ? esr, 0.06 ? esr, input filter capacitor input filter capacitor input filter capacitor input filter capacitor d1 qty: 1 b140, vishay, qty: 1 b140, vishay, qty: 1 b140, vishay, qty: 1 b330, vishay, freewheeling diode freewheeling diode freewheeling diode freewheeling diode l1 qty: 1 cdrh125-100, qty: 1 cdrh127-100, qty: 1 cdrh127-100 qty: 1 up4b-3r3, sumida inductor, sumida inductor, sumida, coiltronics, 10 h 4a, 10 h 5a, 10 h 5a, 3.3 h 11a, output inductor output inductor output inductor output inductor q1 qty: 1 si4800, siliconix, qty: 1 si4884, siliconix, qty: 1 si4884, siliconix, qty: 2 si4884, siliconix low-side mosfet low-side mosfet low-side mosfet low-side mosfet q2 qty: 1 si4800, siliconix, qty: 1 si4800, siliconix, qty: 1 si4800, siliconix, qty: 2 si4884, siliconix, high-side mosfet high-side mosfet high-side mosfet high-side mosfet r2 qty: 1 qty: 1 qty: 1 qty: 1 wsl-2010 .025 1%, wsl-2010 .020 1%, wsl-2512 .015 1%, wsl-2512 .015 1% , vishay, 0.025, 1%, 0.5w, vishay, 0.02, 1%, 0.5w, vishay, 0.015, 1%, 1w, vishay, 0.015, 1%, 1w, current sense resistor current sense resistor current sense resistor current sense resistor u1 mic2182bsm or mic2182bsm or mic2182bsm or mic2182bm mic2182bm mic2182bm mic2182bm table 5. components for 2.5v output 3a (4.5v C 30v) 4a (4.5v C 30v) 5a (4.5v C 8v) 10a (4.5v C 5.5v) reference part no. / description part no. / description part no. / description part no. / description c7 qty: 2 qty: 2 qty: 2 qty: 2 tpse227m010r0100 tpse227m010r0100 tpsv227m010r0060 tpsv447m006r0055 avx, 220 f 10v, avx, 220 f 10v, avx, 220 f 10v, avx, 470 f 6.3v, 0.1 ? esr, 0.1 ? esr, 0.06 ? esr, 0.06 ? esr, output filter capacitor output filter capacitor output filter capacitor output filter capacitor c11 qty: 2 qty: 2 qty: 2 qty: 2 tpse226m035r0300 tpse226m035r0300 tpse226m035r0300 tpsv227m016r0075 avx, 22 f 35v, avx, 22 f 35v, avx, 22 f 35v, avx, 220 f 16v, 0.3 ? esr, 0.3 ? esr, 0.3 ? esr, 0.06 ? esr, input filter capacitor input filter capacitor input filter capacitor input filter capacitor d1 qty: 1 b140, vishay, qty: 1 b140, vishay, qty: 1 b140, vishay, qty: 1 b330, vishay, freewheeling diode freewheeling diode freewheeling diode freewheeling diode l1 qty: 1 cdrh125-100, qty: 1 cdrh127-100, qty: 1 cdrh127-100 qty: 1 up4b-3r3, sumida inductor, sumida inductor, sumida, coiltronics, 10 h 4a, 10 h 5a, 10 h 5a, 3.3 h 11a, output inductor output inductor output inductor output inductor q1 qty: 1 si4800, siliconix, qty: 1 si4884, siliconix, qty: 1 si4884, siliconix, qty: 2 si4884, siliconix low-side mosfet low-side mosfet low-side mosfet low-side mosfet q2 qty: 1 si4800, siliconix, qty: 1 si4800, siliconix, qty: 1 si4800, siliconix, qty: 2 si4884, siliconix, high-side mosfet high-side mosfet high-side mosfet high-side mosfet r2 qty: 1 qty: 1 qty: 1 qty: 2 wsl-2010 .025 1%, wsl-2010 .020 1%, wsl-2512 .015 1%, wsl-2512 .015 1% , vishay, 0.025, 1%, 0.5w, vishay, 0.02, 1%, 0.5w, vishay, 0.015, 1%, 1w, vishay, 0.015, 1%, 1w, current sense resistor current sense resistor current sense resistor current sense resistor u1 mic2182bsm or mic2182bsm or mic2182bsm or mic2182bm mic2182bm mic2182bm mic2182bm table 6. components for 1.8v output
mic2182 micrel mic2182 24 june 2000 effect of soft-start capacitor (c ss ) value on output voltage waveforms during turn-on (10a power supply configuration) effect of soft-start capacitor (c ss ) value on output voltage waveforms during turn-on (4a power supply configuration) normal (300khz switching frequency) and output short-circuit (60khz) conditions switch node (pin 15) waveforms converter waveforms qty: 2 si4884 high-side mosfets switch-node voltage inductor current low-side mosfet gate-to-source voltage high-side mosfet gate-to-source voltage qty: 2 si4884 low-side mosfets v in = 7v l1 = 3.3 h v out = 3.3v i out = 10a v sw pin 15 v sw+hsd pin 16 v gs low-side mosfet v gs high-side mosfet i l1 (2a/div) high-side drive voltage referenced to ground 10amps typical skip-mode waveforms v out v sw pin 15 i l1 (0.5a/div) typical pwm-mode waveforms v out v sw pin 15 i l1 (0.5a/div) power supply operating characteristics
june 2000 25 mic2182 mic2182 micrel -40 -20 0 20 40 60 80 100 0 30 60 90 120 150 180 210 10x10 0 100x10 0 1x10 3 10x10 3 100x10 3 300x10 3 gain (db) phase ( ) frequency (hz) bode plot (4a power supply configuration) gain phase load transient response and bode plot (4a power supply configuration) v in = 12v v out = 3.3v l1 = 10 h r2 = 20m ? i out 2a/div v out load transient response and bode plot (10a power supply configuration) v in = 6v v out = 3.3v l1 = 3.3 h r2 = 7.5m ? i out 5a/div v out -40 -20 0 20 40 60 80 100 0 30 60 90 120 150 180 210 10x10 0 100x10 0 1x10 3 10x10 3 100x10 3 300x10 3 gain (db) phase ( ) frequency (hz) bode plot (10a power supply configuration) gain phase 0 20 40 60 80 100 0.01 0.1 1 10 efficiency (%) output current (a) skip pwm r2 = 7.5m ? l1 = 3.3 efficiency (10a power supply configuration) 0 20 40 60 80 100 0.01 0.1 1 4 efficiency (%) output current (a) skip pwm v in = 5v r2 = 15m ? l1 = 10 5v efficiency (4a power supply configuration) 0 20 40 60 80 100 0.01 0.1 1 4 efficiency (%) output current (a) 12v efficiency (4a power supply configuration) skip pwm v in = 12v r2 = 15m ? l1 = 10 ? l1 = 10 24v efficiency (4a power supply configuration)
mic2182 micrel mic2182 26 june 2000 package information 45 0 C 8 0.244 (6.20) 0.228 (5.79) 0.394 (10.00) 0.386 (9.80) seating plane 0.020 (0.51) ref 0.020 (0.51) 0.013 (0.33) 0.157 (3.99) 0.150 (3.81) 0.050 (1.27) 0.016 (0.40) 0.0648 (1.646) 0.0434 (1.102) 0.050 (1.27) bsc pin 1 dimensions: inches (mm) 0.0098 (0.249) 0.0040 (0.102) 16-pin sop (m) 2.00 (0.079) 1.73 (0.068) 0.21 (0.008) 0.05 (0.002) coplanarity: 0.10 (0.004) max 1.25 (0.049) ref 0.65 (0.0260) bsc 0.875 (0.034) ref 10 4 0 C 8 5.40 (0.213) 5.20 (0.205) 7.90 (0.311) 7.65 (0.301) 6.33 (0.239) 6.07 (0.249) 0.38 (0.015) 0.25 (0.010) 0.22 (0.009) 0.13 (0.005) 0.95 (0.037) 0.55 (0.022) dimensions: mm (inch) 16-pin ssop (sm)
june 2000 27 mic2182 mic2182 micrel
mic2182 micrel mic2182 28 june 2000 micrel inc. 1849 fortune drive san jose, ca 95131 usa tel + 1 (408) 944-0800 fax + 1 (408) 944-0970 web http://www.micrel.com this information is believed to be accurate and reliable, however no responsibility is assumed by micrel for its use nor for an y infringement of patents or other rights of third parties resulting from its use. no license is granted by implication or otherwise under any patent or pat ent right of micrel inc. ? 2000 micrel incorporated

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