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june 2009 1 m9999-063009 micrel, inc. mic2179 mic2179 1.5a synchronous buck regulator general description the micrel mic2179 is a 200khz synchronous buck (step- down) switching regulator designed for high-eficiency, bat - tery-powered applications. the mic2179 operates from a 4.5v to 16.5v input and features internal power mosfets that can supply up to 1.5a output current. it can operate with a maximum duty cycle of 100% for use in low-dropout conditions. it also features a shutdown mode that reduces quiescent current to less than 5a. the mic2179 achieves high eficiency over a wide output current range by operating in either pwm or skip mode. the operating mode is externally selected, typically by an intel- ligent system, which chooses the appropriate mode a ccording to operating conditions, eficiency, and noise requirements. the switching frequency is preset to 200khz and can be synchronized to an external clock signal of up to 300khz. the mic2179 uses current-mode control with internal current sensing. current-mode control provides superior line regula- tion and makes the regulator control loop easy to c ompensate. the output is protected with pulse-by-pulse current limiting and thermal shutdown. undervoltage lockout turns t he output off when the input voltage is less than 4.5v. the mic2179 and is packaged in a 20-lead ssop package with an operating temperature range of C40c to +85c. typical application bias sgnd comp pgnd fb sw vin c2100f 6.3v v out 3.3v/600ma l1 22h c4 6.8nf c30.01f mic 2179-3.3 pwm skip mode pwm mode sync en v in 5.4v to 16.5v c1 10f 20v u1 15 5 13 8 9C12 14 7 1,2,19,20 3,4 16,17 d1mbrm120 pwrgd 6 r120k output good output low pins 4 and 18 are not connected.pins 3 and 4 can be connected together for a low-impedance connection. r54.02k features ? 4.5v to 16.5v input voltage range ? dual-mode operation for high eficiency (up to 96%) pwm mode for > 150ma load current skip mode for <150ma load current ? 150m internal power mosfets at 12v input ? 200khz preset switching frequency ? low quiescent current 1.0ma in pwm mode 600a in skip mode < 5a in shutdown mode ? current-mode control simpliied loop compensation superior line regulation ? 100% duty cycle for low dropout operation ? current limit ? thermal shutdown ? undervoltage lockout applications ? high-eficiency, battery-powered supplies ? buck (step-down) dc-to-dc converters ? cellular telephones ? laptop computers ? hand-held instruments ? battery charger micrel, inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel + 1 (408) 944-0800 ? fax + 1 (408 ) 474-1000 ? http://www.micrel.com downloaded from: http:///
micrel, inc. mic2179 june 2009 2 m9999-063009 ordering information part number voltage temperature range package standard* pb-free mic2179bsm mic2179ysm adj. -40c to +85c 20-lead ssop mic2179-3.3bsm mic2179-3.3ysm 3.3v -40c to +85c 20-lead ssop mic2179-5.0bsm mic2179-5.0ysm 5.0v -40c to +85c 20-lead ssop * standard product will be supported as pb-free iaw pccn #040004 effective 1-1-2005 pending residual depletion. pin description pin number pin name pin function 1, 2, 19, 20 pgnd power ground: connect all pins to central ground point. 3 sw switch (output): internal power mosfet output switches. 5 pwm pwm/skip-mode control (input): logic-level input. controls regulator operating mode. logic low enables pwm mode. logic high enables skip mode. do not allow pin to loat. 6 pwrgd error flag (output): open-drain output. active low when fb input is 10% below the reference voltage (v ref ). 7 fb feedback (input): connect to output voltage divider resistors. 8 comp compensation: output of internal error ampliier. connect capacitor or series rc network to compensate the regulator control loop. 9C12 sgnd signal ground: connect all pins to ground, pgnd. 13 sync frequency synchronization (input): optional. connect an external clock signal to synchronize the oscillator. leading edge of signal above 1.7v terminates switching cycle. connect to sgnd if not used. 14 bias internal 3.3v bias supply: decouple with 0.01f bypass capacitor to sgnd. do not apply any external load. 15 en enable (input): logic high enables operation. logic low shuts down regulator. do not allow pin to loat. 16, 17 vin supply voltage (input): requires bypass capacitor to pgnd. both pins must be connected to v in . 4, 18 nc not internally connected. pin coniguration 2 pgnd 3 sw 4 nc 5 pwrgd 6 pwm 7 fb 1 pgnd 8 comp 9 sgnd pgnd 20 pgnd 19 nc 18 vin 17 vin 16 en 15 10 sgnd 14 13 12 11 sgnd sgnd sync bias 20-lead wide ssop downloaded from: http:///
june 2009 3 m9999-063009 micrel, inc. mic2179 electrical characteristics (3) v in = 7.0v; t a = 25c, bold indicates C40c t a 85c; unless noted. symbol parameter condition min typ max units i ss input supply current pwm mode, output not switching, 1.0 1.5 ma 4.5v v in 16.5v skip mode, output not switching, 600 750 a 4.5v v in 16.5v v en = 0v, 4.5v v in 16.5v 1 25 a v bias bias regulator output voltage v in = 16.5v 3.10 3.30 3.4 v v fb feedback voltage mic2179 [adj.]: v out = 3.3v, i load = 0 1.22 1.245 1.27 v v out output voltage mic2179 [adj.]: v out = 3.3v, 3.20 3.3 3.40 v 5v v in 16v, 10ma i load 1a 3.14 3.46 v mic2179-5.0: i load = 0 4.85 5.0 5.15 v mic2179-5.0: 4.85 5.0 5.15 6v v in 16v, 10ma i load 1a 4.75 5.25 v mic2179-3.3: i load = 0 3.20 3.3 3.40 v mic2179-3.3: 3.20 3.3 3.40 v 5v v in 16v, 10ma i load 1a 3.14 3.46 v v th undervoltage lockout upper threshold 4.25 4.35 v v tl lower threshold 3.90 4.15 v i fb feedback bias current mic2179 [adj.] 60 150 na mic2179-5.0, mic2179-3.3 20 40 a a vol error ampliier gain 0.6v v comp 0.8v 15 18 20 error ampliier output swing upper limit 0.9 1.5 v lower limit 0.05 0.1 v error ampliier output current source and sink 15 25 35 a f o oscillator frequency 160 200 240 khz d max maximum duty cycle v fb = 1.0v 100 % t on min minimum on-time v fb = 1.5v 300 400 ns sync frequency range 220 300 khz sync threshold 0.8 1.6 2.2 v sync minimum pulse width 500 ns i sync sync leakage v sync = 0v to 5.5v C1 0.01 1 a i lim current limit pwm mode, v in = 12v 3.4 4.3 5.5 a skip mode 600 ma r on switch on-resistance high-side switch, v in = 12v 160 350 m low-side switch, v in = 12v 140 350 m i sw output switch leakage v sw = 16.5v 1 10 a absolute maximum ratings (1) supply voltage [100ms transient] (v in ) ......................... 18v output switch voltage (v sw ) ................................................... 18v output switch current (i sw ) ......................................... 6.0a enable, pwm control voltage (v en , v pwm ) .................. 18v sync voltage (v sync ) ...................................................... 6v operating ratings (2) supply voltage (v in ) .......................................4.5v to 16.5v junction temperature range (t j ) ............ C40c to +125c downloaded from: http:///
micrel, inc. mic2179 june 2009 4 m9999-063009 symbol parameter condition min typ max units enable threshold 0.8 1.6 2.2 v i en enable leakage v en = 0v to 5.5v C1 0.01 1 a pwm threshold 0.6 1.1 1.4 v i pwm pwm leakage v pwm = 0v to 5.5v C1 0.01 1 a pwrgd threshold mic2179 [adj.]: measured at fb pin 1.09 1.13 1.17 v mic2179-5.0: measured at fb pin 4.33 4.54 4.75 v mic2179-3.3: measured at fb pin 2.87 3.00 3.13 v pwrgd output low i sink = 1.0ma 0.25 0.4 v pwrgd off leakage v pwrgd = 5.5v 0.01 1 a notes:1. exceeding the absolute maximum rating may damage the device. 2. the device is not guaranteed to function outside its operating rating. 3. speciication for packaged product only. general. devices are esd sensitive. handling precautions recommended. downloaded from: http:///
june 2009 5 m9999-063009 micrel, inc. mic2179 typical characteristics 175 180 185 190 195 200 205 -60 -30 0 30 60 90 120 150 frequency (khz) temperature (c) oscillator frequency vs. temperature 1.238 1.240 1.242 1.244 1.246 1.248 1.250 1.252 -60 -30 0 30 60 90 120 150 reference voltage (v) temperature (c) reference voltage vs. temperature mic2179 [adj.] 3.280 3.285 3.290 3.295 3.300 3.305 3.310 3.315 3.320 -60 -30 0 30 60 90 120 150 reference voltage (v) temperature (c) reference voltage vs. temperature mic2179-3.3 4.970 4.980 4.990 5.000 5.010 5.020 5.030 -60 -30 0 30 60 90 120 150 reference voltage (v) temperature (c) reference voltage vs. temperature mic2179-5.0 16.0 16.5 17.0 17.5 18.0 18.5 19.0 -60 -30 0 30 60 90 120 150 amplifier voltage gain temperature (c) error-amplifier gain vs. temperature 0 20 40 60 80 100 120 -60 -30 0 30 60 90 120 150 bias current (na) temperature (c) feedback input bias current vs. temperature 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 -60 -30 0 30 60 90 120 150 current limit (a) temperature (c) current limit vs. temperature 0 50 100 150 200 250 300 350 2 10 12 14 16 18 on-resistance (m?) input voltage (v) high-side switch on-resistance 125c 85c 25c 0c 4 6 8 0 50 100 150 200 250 300 350 400 2 10 12 14 16 18 on-resistance (m?) input voltage (v) low-side switch on-resistance 125c 85c 25c 0c 4 6 8 0 2 4 6 8 10 12 2 10 12 14 16 18 supply current (ma) input voltage (v) pwm-mode supply-current output switching 4 6 8 60 65 70 75 80 85 90 95 10 100 600 efficiency (%) output current (ma) 5.4v pwm 8.4v pwm 8.4v skip 5.4v skip skip- and pwm-mode efficiency downloaded from: http:///
micrel, inc. mic2179 june 2009 6 m9999-063009 block diagram sw pgnd i sense amp. pwm/ skip-mode select v ref 1.245v 110m ? n-channel 110m ? p-channel comp vin skip-modecomp. i limit comp. output control logic power good comp. 1.13v r s q 200khz oscillator pwm comp. 3.3v regulator uvlo, thermal shutdown v out l fb sgnd c c pwrgd 0.01f en bias v in 4.5v to 16.5v 100f sync c out mic2179 [adjustable] internal supply voltage enable shutdown stop 1514 13 6 8 17 16 3 d 12 19 20 r1r2 7 9 10 11 12 bold lines indicate high current traces i limit thresh. voltage pwm skip mode pwm mode 5 v in output good 20k * * connect s gnd to p gnd r c resetpulse correctiveramp v out 1.245 r1 r2 1 r3 4.02k v out = 1.245 ( + 1 ) r1 r2 downloaded from: http:///
june 2009 7 m9999-063009 micrel, inc. mic2179 functional description micrels mic2179 is a synchronous buck regulator that oper- ates from an input voltage of 4.5v to 16.5v and provides a regulated output voltage of 1.25v to 16.5v. its has internal power mosfets that supply up to 1.5a load current and operates with up to 100% duty cycle to allow low-dropout operation. to optimize eficiency, the mic2179 operates in pwm and skip mode. skip mode provides the best eficiency when load current is less than 150ma, while pwm mode is more eficient at higher current. pwm or skip-mode opera - tion is selected externally, allowing an intelligent system (i.e. microprocessor controlled) to select the correct operating mode for eficiency and noise requirements. during pwm operation, the mic2179 uses current-mode control which provides superior line regulation and makes the control loop easier to compensate. the pwm switching frequency is set internally to 200khz and can be sy nchronized to an external clock frequency up to 300khz. other features include a low-current shutdown mode, current limit, under- voltage lockout, and thermal shutdown. see the following sections for more detail. switch output the switch output (sw) is a half h-bridge consisting of a high-side p-channel and low-side n-channel power mo sfet. these mosfets have a typical on-resistance of 150m when the mic2179 operates from a 12v supply. antishoot-through circuitry prevents the p-channel and n-channel from turning on at the same time. current limit the mic2179 uses pulse-by-pulse current limiting to protect the output. during each switching period, a current limit com- parator detects if the p-channel current exceeds 4.3a. when it does, the p-channel is turned off until the next switching period begins. undervoltage lockout undervoltage lockout (uvlo) turns off the output when the input voltage (v in ) is to low to provide suficient gate drive for the output mosfets. it prevents the output from turning on until v in exceeds 4.3v. once operating, the output will not shut off until v in drops below 4.2v. thermal shutdown thermal shutdown turns off the output when the mic2179 junction temperature exceeds the maximum value for safe operation. after thermal shutdown occurs, the output will not turn on until the junction temperature drops approximately 10c. shutdown mode the mic2179 has a low-current shutdown mode that is con- trolled by the enable input (en). when a logic 0 is applied to en, the mic2179 is in shutdown mode, and its quiescent current drops to less than 5a. internal bias regulator an internal 3.3v regulator provides power to the mic2179 control circuits. this internal supply is brought out to the bias pin for bypassing by an external 0.01f capacitor. do not connect an external load to the bias pin. it is not designed to provide an external supply voltage. frequency synchronization the mic2179 operates at a preset switching frequency of 200khz. it can be synchronized to a higher frequency by con- necting an external clock to the sync pin. the sync pin is a logic level input that synchronizes the oscillator to the rising edge of an external clock signal. it has a frequency range of 220khz to 300khz, and can operate with a minimum pulse width of 500ns. if synchronization is not required, connect sync to ground. power good flag the power good lag (pwrgd) is an error lag that alerts a system when the output is not in regulation. when the output voltage is 10% below its nominal value, pwrgd is logic low, signaling that v out is to low. pwrgd is an open-drain output that can sink 1ma from a pull-up resistor connected to v in . low-dropout operation output regulation is maintained in pwm or skip mode even when the difference between v in and v out decreases below 1v. as v in C v out decreases, the duty cycle increases until it reaches 100%. at this point, the p-channel is kept on for several cycles at a time, and the output stays in regulation until v in C v out falls below the dropout voltage (dropout voltage = p-channel on-resistance load current). pwm-mode operation refer to pwm mode functional diagram which is a simpli- ied block diagram of the mic2179 operating in pwm mode and its associated waveforms. when operating in pwm mode, the output p-channel and n- channel mosfets are alternately switched on at a constant frequency and variable duty cycle. a switching period begins when the oscillator generates a reset pulse. this pulse resets the rs latch which turns on the p-channel and turns off the n-channel. during this time, inductor current (i l1 ) increases and energy is stored in the inductor. the current sense ampli- ier (i sense amp) measures the p-channel drain-to-source voltage and outputs a voltage proportional to i l1 . the output of i sense amp is added to a sawtooth waveform (corrective ramp) generated by the oscillator, creating a composite wave - form labeled i sense on the timing diagram. when i sense is greater than the error ampliier output, the pwm comparator will set the rs latch which turns off the p-channel and turns on the n-channel. energy is then discharged from the induc- tor and i l1 decreases until the next switching cycle begins. by varying the p-channel on-time (duty cycle), the average inductor current is adjusted to whatever value is required to regulate the output voltage. the mic2179 uses current-mode control to adjust the duty cycle and regulate the output voltage. current-mode control has two signal loops that determine the duty cycle. one is an outer loop that senses the output voltage, and the other is a faster inner loop that senses the inductor current. signals from these two loops control the duty cycle in the following way: v out is fed back to the error ampliier which compares the feedback voltage (v fb ) to an internal reference voltage downloaded from: http:///
micrel, inc. mic2179 june 2009 8 m9999-063009 (v ref ). when v out is lower than its nominal value, the error ampliier output voltage increases. this voltage the n intersects the current sense waveform later in switching period which increases the duty cycle and the average inductor current. if v out is higher than nominal, the error ampliier output voltage decreases, reducing the duty cycle. the pwm control loop is stabilized in two ways. first, the inner signal loop is compensated by adding a corrective ramp to the output of the current sense ampliier. this allows the regulator to remain stable when operating at greater than 50% duty cycle. second, a series resistor-capacitor load is connected to the error ampliier output (comp pin). this places a pole-zero pair in the regulator control loop. one more important item is synchronous rectiication. as mentioned earlier, the n-channel output mosfet is turned on after the p-channel turns off. when the n-channel turns on, its on-resistance is low enough to create a short across the output diode. as a result, inductor current lows through the n-channel and the voltage drop across it is signiicantly lower than a diode forward voltage. this reduces power dis- sipation and improves eficiency to greater than 95% under certain operating conditions. to prevent shoot through current, the output stage employs break-before-make circuitry that provides approxima tely 50ns of delay from the time one mosfet turns off and the other turns on. as a result, inductor current briely lows through the output diode during this transition. skip-mode operation refer to skip mode functional diagram which is a simpliied block diagram of the mic2179 operating in skip mode and its associated waveforms. skip-mode operation turns on the output p-channel at a frequency and duty cycle that is a function of v in , v out , and the output inductor value. while in skip mode, the n-chan- nel is kept off to optimize eficiency by reducing gate charge dissipation. v out is regulated by skipping switching cycles that turn on the p-channel. to begin analyzing mic2179 skip mode operation, assume the skip-mode comparator output is high and the latch out- put has been reset to a logic 1. this turns on the p-channel and causes i l1 to increase linearly until it reaches a current limit of 400ma. when i l1 reaches this value, the current limit comparator sets the rs latch output to logic 0, turning off the p-channel. the output switch voltage (v sw ) then swings from v in to 0.4v below ground, and i l1 lows through the schottky diode. l1 discharges its energy to the output and i l1 decreases to zero. when i l1 = 0, v sw swings from C0.4v to v out , and this triggers a one-shot that resets the rs latch. resetting the rs latch turns on the p-channel, and this begins another switching cycle. the skip-mode comparator regulates v out by controlling when the mic2179 skips cycles. it compares v fb to v ref and has 10mv of hysteresis to prevent oscillations in the control loop. when v fb is less than v ref C 5mv, the com- parator output is logic 1, allowing the p-channel to turn on. conversely, when v fb is greater than v ref + 5mv, the p- channel is turned off. note that this is a self oscillating topology which explains why the switching frequency and duty cycle are a function of v in , v out , and the value of l1. it has the unique feature (for a pulse-skipping regulator) of supplying the same value of maximum load current for any value of v in , v out , or l1. this allows the mic2179 to always supply up to 300ma of load current when operating in skip mode. selecting pwm- or skip-mode operation pwm or skip mode operation is selected by an external logic signal applied to the pwm pin. a logic low places the mic2179 into pwm mode, and logic high places it into skip mode. skip mode operation provides the best eficiency when load current is less than 150ma, and pwm operation is more eficient at higher currents. the mic2179 was designed to be used in intelligent sys- tems that determine when it should operate in pwm or skip mode. this makes the mic2179 ideal for applications where a regulator must guarantee low noise operation when sup- plying light load currents, such as cellular telephone, audio, and multimedia circuits. there are two important items to be aware of when selecting pwm or skip mode. first, the mic2179 can start-up only in pwm mode, and therefore requires a logic low at pwm dur- ing start-up. second, in skip mode, the mic2179 will supply a maximum load current of approximately 300ma, so the output will drop out of regulation when load current exceeds this limit. to prevent this from occurring, the mic2179 should change from skip to pwm mode when load current exceeds 200ma. downloaded from: http:///
june 2009 9 m9999-063009 micrel, inc. mic2179 sw pgnd i sense amp. v ref 1.245v 110m ? n-channel 110m ? p-channel comp vin error amp. r s q 200khz oscillator pwm comp. v out l1 fb sgnd c c v in 4.5v to 16.5v c in syn c c out mic2179 [adjustable] pwm-mode signal path stop 13 8 1716 d r1 r2 7 r c corrective ram p reset pulse i l1 91 01 11 2 31 2 19 20 v out = 1.245 ( + 1 ) r1 r2 v sw i l1 reset pulse i sense i load ? i l1 error amp. o utput pwm-mode functional diagram downloaded from: http:///
micrel, inc. mic2179 june 2009 10 m9999-063009 s r q one shot sw pgnd i sense amp. v ref 1.245v 110m ? p-channel vin skip-mode comp. i limit comp. v out l1 fb sgnd v in 4.5v to 16.5v c in c out mic2179 [adjustable] skip-mode signal path 1716 d r1 r2 i limit thresh . voltage output control logic i l1 31 2 19 20 91 01 11 2 7 v out = 1.245 ( + 1 ) r1 r2 v sw i l1 o ne-shot pulse v fb v ref + 5mv v ref C 5mv 0 i lim 0 v out v in skip-mode functional diagram downloaded from: http:///
june 2009 11 m9999-063009 micrel, inc. mic2179 application information feedback resistor selection (adjustable version) the output voltage is programmed by connecting an external resistive divider to the fb pin as shown in mic2179 block diagram. the ratio of r1 to r2 determines the out put voltage. to optimize eficiency during low output current operation, r2 should not be less than 20k. however, to prevent feedback error due to input bias current at the fb pin, r2 should not be greater than 100k. after selecting r2, calculate r1 with the following formula: r1 = r2 (( ) -1 ) 1.245v v out input capacitor selection the input capacitor is selected for its rms current and voltage rating and should be a low esr (equivalent series resistance) electrolytic or tantalum capacitor. as a rule of thumb, the voltage rating for a tantalum capacitor should be twice the value of v in , and the voltage rating for an electrolytic should be 40% higher than v in. the rms current rating must be equal or greater than the maximum rms input ripple cur- rent. a simple, worst case formula for calculating this rms current is: i rms(max) = 2 i load(max) tantalum capacitors are a better choice for applications that require the most compact layout or operation below 0c. the input capacitor must be located very close to the vin pin (within 0.2in, 5mm). also, place a 0.1f ceramic bypass capacitor as close as possible to vin. inductor selection the mic2179 is a current-mode controller with internal slope compensation. as a result, the inductor must be at least a minimum value to prevent subharmonic oscillations. this minimum value is calculated by the following formula: l min = v out x 3.0 h/v in general, a value at least 20% greater than l min should be selected because inductor values have a tolerance of 20%. two other parameters to consider in selecting an inductor are winding resistance and peak current rating. the inductor must have a peak current rating equal or greater than the peak inductor current. otherwise, the inductor may satu- rate, causing excessive current in the output switch. also, the inductors core loss may increase signiicantly. both of these effects will degrade eficiency. the formula for peak inductor current is: i l(peak) = i load(max) + 2 ?i l(max) where: ?i l(max) = v out ( 1 - ) x v ou t v in(max) 1 l ? f to maximize eficiency, the inductors resistance must be less than the output switch on-resistance (preferably, 50m or less). output capacitor selection select an output capacitor that has a low value of esr. this parameter determines a regulators output ripple volt- age (v ripple ) which is generated by ? i l esr. therefore, esr must be equal or less than a maximum value calculated for a speciied v ripple (typically less than 1% of the output voltage) and ? i l(max) : esr max = ?i l(max) v ripple typically, capacitors in the range of 100 to 220f have esr less than this maximum value. the output capacitor can be a low esr electrolytic or tantalum capacitor, but tantalum is a better choice for compact layout and operation at tempera- tures below 0c. the voltage rating of a tantalum capacitor must be 2 v out , and the voltage rating of an electrolytic must be 1.4 v out . output diode selection in pwm operation, inductor current lows through the output diode approximately 50ns during the dead time when one output mosfet turns off the other turns on. in skip mode, the inductor current lows through the diode during the entire p-channel off time. the correct diode for both of these condi- tions is a 1a diode with a reverse voltage rating greater than v in . it must be a schottky or ultrafast-recovery diode (t r < 100ns) to minimize power dissipation from the diodes reverse-recovery charge.compensation compensation is provided by connecting a series rc load to the comp pin. this creates a pole-zero pair in the regu- lator control loop, allowing the regulator to remain stable with enough low frequency loop-gain for good load and line regulation. at higher frequencies, the pole-zero reduces loop-gain to a level referred to as the mid-band gain. the mid-band gain is low enough so that the loop gain crosses 0db with suficient phase margin. typical values for the rc load are 4.7nf to 10nf for the capacitor and 5k to 20k for the resistor. printed circuit board layout a well designed pc board will prevent switching noise and ground bounce from interfering with the operation of the mic2179. a good design takes into consideration component placement and routing of power traces. the irst thing to consider is the locations of the input ca - pacitor, inductor, output diode, and output capacitor. the input capacitor must be placed very close to the vin pin, the inductor and output diode very close to the sw pin, and the output capacitor near the inductor. these components pass large high-frequency current pulses, so they must use short, wide power traces. in addition, their ground pins and pgnd are connected to a ground plane that is nearest the power supply ground bus. downloaded from: http:///
micrel, inc. mic2179 june 2009 12 m9999-063009 the feedback resistors, rc compensation network, and bias pin bypass capacitor should be located close to their respective pins. to prevent ground bounce, their ground traces and sgnd should not be in the path of switching currents returning to the power supply ground bus. sgnd and pgnd should be tied together by a ground plane that extends under the mic2179. suggested manufacturers list inductors capacitors diodes transistors coilcraft avx corp. general instruments (gi) siliconix 1102 silver lake rd. 801 17th ave. south 10 melville park rd. 2201 laurelwood rd. cary, il 60013 myrtle beach, sc 29577 melville, ny 11747 santa clara, ca 96056 tel: (708) 639-2361 tel: (803) 448-9411 tel: (516) 847-3222 tel: (800) 554-5565 fax: (708) 639-1469 fax: (803) 448-1943 fax: (516) 847-3150 coiltronics sanyo video components corp. international rectiier corp. 6000 park of commerce blvd. 2001 sanyo ave. 233 kansas st. boca raton, fl 33487 san diego, ca 92173 el segundo, ca 90245 tel: (407) 241-7876 tel: (619) 661-6835 tel: (310) 322-3331 fax: (407) 241-9339 fax: (619) 661-1055 fax: (310) 322-3332 bi technologies sprague electric motorola inc. 4200 bonita place lower main st. ms 56-126 fullerton, ca 60005 sanford, me 04073 3102 north 56th st. tel: (714) 447-2345 tel: (207) 324-4140 phoenix, az 85018 fax: (714) 447-2500 tel: (602) 244-3576 fax: (602) 244-4015 downloaded from: http:///
june 2009 13 m9999-063009 micrel, inc. mic2179 micrel inc. 2180 fortune drive san jose, ca 95131 usa tel + 1 (408) 944-0800 fa x + 1 (408) 474-1000 w e b http://www.micrel.com this information furnished by micrel in this data sheet is believed to be accurate and reliable. however no responsibility is assumed by micrel for its use. micrel reserves the right to change circuitry and speciications at any time without notiication to t he customer. micrel products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a signiicant injury to the user. a purchaser's use or sale of micrel products for use in life support appliances, devices or systems is a purchaser's own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2001 micrel incorporated package information 20-pin ssop (sm) downloaded from: http:///

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