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march 2005 1 m9999-031805 mic2178 micrel, inc. mic2178 2.5a synchronous buck regulator general description the micrel mic2178 is a 200khz synchronous buck (step- down) switching regulator designed for high-efficiency, bat- tery-powered applications. the mic2178 operates from a 4.5v to 16.5v input and features internal power mosfets that can supply up to 2.5a 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 5 a. the mic2178 achieves high efficiency over a wide output current range by operating in either pwm or skip mode. the operating mode is externally selected, typically by an intelli- gent system, which chooses the appropriate mode according to operating conditions, efficiency, and noise requirements. the switching frequency is preset to 200khz and can be synchronized to an external clock signal of up to 300khz. the mic2178 uses current-mode control with internal current sensing. current-mode control provides superior line regula- tion and makes the regulator control loop easy to compen- sate. the output is protected with pulse-by-pulse current limiting and thermal shutdown. undervoltage lockout turns the output off when the input voltage is less than 4.5v. the mic2178 and is packaged in a 20-lead wide power soic package with an operating temperature range of C40 c to +85 c. see the mic2177 for automatic selection of pwm or skip- mode operation. t ypical application features ?4 .5v to 16.5v input voltage range ? dual-mode operation for high efficiency (up to 96%) pwm mode for > 200ma load current skip mode for < 200ma load current ? 100m ? internal power mosfets at 12v input ? 200khz preset switching frequency ? low quiescent current 1.0ma in pwm mode 600 a in skip mode < 5 a in shutdown mode ? current-mode control simplified loop compensation superior line regulation ? 100% duty cycle for low dropout operation ?curr ent limit ? thermal shutdown ?u ndervoltage lockout applications ?h igh-efficiency, battery-powered supplies ? buck (step-down) dc-to-dc converters ? palmtop computers ? laptop computers ? cellular telephones ?h and-held instruments ? battery chargers bias sgnd en comp pgnd fb out vin c5 220 f 10v v out 5v/2.5a l1, 33 h c3 6.8nf c4 0.01 f r2 10k mic2178-5.0 pwm sync r1 10k v in 5.4v to 18v c2 22 f 35v u1 20 18 10 13 14C17 19 12 4C7 3,8 1,2,9 d1 mbrs140 sw 10 enable on off pwrgd 11 r1 20k skip mode pwm mode ouput good output low c6 220 f 10v c1 22 f 35v 70 75 80 85 90 95 100 10 100 1000 2500 efficiency (%) output current (ma) 5v output efficiency v in = 6v skip pwm micrel, inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel + 1 (408) 944-0800 ? fax + 1 (408) 474-1000 ? http://www.mic rel.com
mic2178 micrel, inc. m9999-031805 2 march 2005 pin description pin number pin name pin function 1, 2, 9 vin supply voltage (input): requires bypass capacitor to pgnd. all three pins must be connected to v in . 3, 8 sw switch (output): internal power mosfet output switches. both pins must be externally connected together. 4, 5, 6, 7 pgnd power ground: connect all pins to central ground point. 10 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 float. 11 pwrgd error flag (output): open-drain output. active low when fb input is 10% below the reference voltage (v ref ). 12 fb feedback (input): connect to output voltage divider resistors. 13 comp compensation: output of internal error amplifier. connect capacitor or series rc network to compensate the regulator control loop. 14, 15, 16, 17 sgnd signal ground: connect all pins to ground, pgnd*. 18 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. 19 bias internal 3.3v bias supply: decouple with 0.01 f bypass capacitor to sgnd. do not apply any external load. 20 en enable (input): logic high enables operation. logic low shuts down regulator. do not allow pin to float. pin configuration 2 vin 3 sw 4 pgnd 5 pgnd 6 pgnd 7 pgnd 1 vin 8 sw 9 vin en 20 bias 19 sync 18 sgnd 17 sgnd 16 sgnd 15 10 pwm 14 13 12 11 pwrgd fb comp sgnd 20-lead wide power soic ordering information part number standard* pb-free voltage junction temp. package mic2178bwm mic2178ywm adj C40 c to +85 c 20-lead wsoic mic2178-3.3bwm mic2178-3.3ywm 3.3v C40 c to +85 c 20-lead wsoic mic2178-5.0bwm mic2178-5.0ywm 5.0v C40 c to +85 c 20-lead wsoic * standard product will be supported as pb-free iaw ppcn #040004 effective 1-1-2005.
march 2005 3 m9999-031805 mic2178 micrel, inc. absolute maximum ratings 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 supply voltage (v in ) ..................................... 4.5v to 16.5v junction temperature range (t j ) ........... C40 c to +125 c electrical characteristics v in = 7.0v; t a = 25 c, bold indicates C40 c t a 85 c; 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 mic2178 [adj.]: v out = 3.3v, i load = 0 1.22 1.245 1.27 v v out output voltage mic2178 [adj.]: v out = 3.3v, 3.20 3.3 3.40 v 5v v in 16v, 10ma i load 2a 3.14 3.46 v mic2178-5.0: i load = 0 4.85 5.0 5.15 v mic2178-5.0: 4.85 5.0 5.15 6v v in 16v, 10ma i load 2a 4.75 5.25 v mic2178-3.3: i load = 0 3.20 3.3 3.40 v mic2178-3.3: 3.20 3.3 3.40 v 5v v in 16v, 10ma i load 2a 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 mic2178 [adj.] 60 150 na mic2178-5.0, mic2178-3.3 20 40 a a vol error amplifier gain 0.6v v comp 0.8v 15 18 20 error amplifier output swing upper limit 0.9 1.5 v lower limit 0.05 0.1 v error amplifier 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 3.8 4.7 5.7 a skip mode 600 ma r on switch on-resistance high-side switch, v in = 12v 90 250 m ? low-side switch, v in = 12v 110 250 m ? i sw output switch leakage v sw = 16.5v 1 10 a
mic2178 micrel, inc. m9999-031805 4 march 2005 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 mic2178 [adj.]: measured at fb pin 1.09 1.13 1.17 v mic2178-5.0: measured at fb pin 4.33 4.54 4.75 v mic2178-3.3: 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 general note: devices are esd sensitive. handling precautions recommended.
march 2005 5 m9999-031805 mic2178 micrel, inc. t ypical 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 mic2178 [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 mic2178-3.3 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 mic2178-5.0 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 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5.0 -60 -30 0 30 60 90 120 150 current limit (a) temperature ( c) current limit vs. temperature 0 50 100 150 200 250 246810121 41618 on-resistance (m ? ) input voltage (v) high-side switch on-resistance 125 c 85 c 25 c 0 c 0 50 100 150 200 250 300 350 246810121 41618 on-resistance (m ? ) input voltage (v) low-side switch on-resistance 125 c 85 c 25 c 0 c 0 2 4 6 8 10 12 246810121 41618 supply current (ma) input voltage (v) pwm-mode supply current output switching 60 65 70 75 80 85 90 95 100 10 100 1000 2500 efficiency (%) output current (ma) v in = 5v 8v 12v 3.3v output efficiency skip pwm 70 75 80 85 90 95 100 10 100 1000 2500 efficiency (%) output current (ma) 8v 12v 5v output efficiency v in = 6v skip pwm
mic2178 micrel, inc. m9999-031805 6 march 2005 block diagram sw pgnd i sense amp. pwm/ skip-mode select v ref 1.245v 100m ? n-channel 100m ? p-channel comp vin skip-mode comp. 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 0.01 f 10k en bias v in 4.5v to 16.5v 100 f sync c out mic2178 [adjustable] internal supply voltage enable shutdown stop 20 19 18 11 13 2 1 3 8 d 4 5 6 7 r1 r2 12 14 15 16 17 bold lines indicate high current traces i limit thresh. volt age pwm skip mode pwm mode 10 v in output good 20k * *c onnect s gnd to p gnd r c reset pulse corrective ramp v out 1.245 r1 r2 1 9
march 2005 7 m9999-031805 mic2178 micrel, inc. functional description micrels mic2178 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 2.5a load current and operates with up to 100% duty cycle to allow low-dropout operation. to optimize efficiency, the mic2178 operates in pwm and skip mode. skip mode provides the best efficiency when load current is less than 200ma, while pwm mode is more efficient at higher current. pwm or skip-mode operation is selected externally, allowing an intelligent system (i.e. microprocessor controlled) to select the correct operating mode for efficiency and noise requirements. during pwm operation, the mic2178 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 synchro- nized to an external clock frequency up to 300khz. other features include a low-current shutdown mode, current limit, undervoltage lockout, and thermal shutdown. see the follow- ing 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 mosfet. these mosfets have a typical on-resistance of 100m ? when the mic2178 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 mic2178 uses pulse-by-pulse current limiting to protect the output. during each switching period, a current limit comparator detects if the p-channel current exceeds 4.7a. 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 sufficient 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 mic2178 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 10 c. shutdown mode the mic2178 has a low-current shutdown mode that is controlled by the enable input (en). when a logic 0 is applied to en, the mic2178 is in shutdown mode, and its quiescent current drops to less than 5 a. internal bias regulator an internal 3.3v regulator provides power to the mic2178 control circuits. this internal supply is brought out to the bias pin for bypassing by an external 0.01 f capacitor. do not connect an external load to the bias pin. it is not designed to provide an external supply voltage. frequency synchronization the mic2178 operates at a preset switching frequency of 200khz. it can be synchronized to a higher frequency by connecting 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 220khzC300khz, 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 flag (pwrgd) is an error flag 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- fied block diagram of the mic2178 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 amplifier (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 waveform labeled i sense on the timing diagram. when i sense is greater than the error amplifier output, the pwm comparator will set the rs latch which turns off the p- channel and turns on the n-channel. energy is then dis- charged from the inductor 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 mic2178 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 amplifier which compares the feedback voltage (v fb ) to an internal reference voltage
mic2178 micrel, inc. m9999-031805 8 march 2005 (v ref ). when v out is lower than its nominal value, the error amplifier output voltage increases. this voltage then inter- sects 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 amplifier 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 amplifier. 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 amplifier output (comp pin). this places a pole-zero pair in the regulator control loop. one more important item is synchronous rectification. 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 flows through the n-channel and the voltage drop across it is significantly lower than a diode forward voltage. this reduces power dissipation and improves efficiency to greater than 95% under certain operating conditions. to prevent shoot through current, the output stage employs break-before-make circuitry that provides approximately 50ns of delay from the time one mosfet turns off and the other turns on. as a result, inductor current briefly flows through the output diode during this transition. skip-mode operation refer to skip mode functional diagram which is a simplified block diagram of the mic2178 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-channel is kept off to optimize efficiency by reducing gate charge dissipation. v out is regulated by skipping switching cycles that turn on the p-channel. to begin analyzing mic2178 skip mode operation, assume the skip-mode comparator output is high and the latch output 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 600ma. 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 flows through the schottky diode. l1 discharges its energy to the output and i l1 de- creases 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 mic2178 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 C5mv, the comparator output is logic 1, allowing the p-channel to turn on. con- versely, 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 mic2178 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 mic2178 into pwm mode, and logic high places it into skip mode. skip mode operation provides the best efficiency when load current is less than 200ma, and pwm operation is more efficient at higher currents. the mic2178 was designed to be used in intelligent systems that determine when it should operate in pwm or skip mode. this makes the mic2178 ideal for applications where a regulator must guarantee low noise operation when supply- ing 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 mic2178 can start-up only in pwm mode, and therefore requires a logic low at pwm during start-up. second, in skip mode, the mic2178 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 mic2178 should change from skip to pwm mode when load current exceeds 200ma.
march 2005 9 m9999-031805 mic2178 micrel, inc. sw pgnd i sense amp. v ref 1.245v 100m ? n-channel 100m ? 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 sync c out mic2178 [adjustable] pwm-mode signal path stop 18 13 2 1 3 8 d 4 5 6 7 r1 r2 12 14 15 16 17 r c corrective ramp reset pulse i l1 v out 1.245 r1 r2 1 9 v sw i l1 reset pulse i sense i load ? i l1 error amp. output pwm-mode functional diagram
mic2178 micrel, inc. m9999-031805 10 march 2005 s r q one shot sw pgnd i sense amp. v ref 1.245v 100m ? 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 mic2178 [adjustable] skip-mode signal path 2 1 3 8 d 4 5 6 7 r1 r2 12 14 15 16 17 i limit thresh. voltage output control logic i l1 v out 1.245 r1 r2 1 9 v sw i l1 one-shot pulse v fb v ref + 5mv v ref C 5mv 0 i lim 0 v out v in skip-mode functional diagram
march 2005 11 m9999-031805 mic2178 micrel, inc. 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 mic2178 block diagram. the ratio of r1 to r2 determines the output voltage. to optimize efficiency 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 v 1.245v out ? ? ? ? ? ? ? ? ? ? ? ? C 1 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 current. a simple, worst case formula for calculating this rms current is: i = i rms(max) load(max) 2 tantalum capacitors are a better choice for applications that require the most compact layout or operation below 0 c. the input capacitor must be located very close to the vin pin (within 0.2in, 5mm). also, place a 0.1 f ceramic bypass capacitor as close as possible to vin. inductor selection the mic2178 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 = v 3.0 h/v min out 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 saturate, causing excessive current in the output switch. also, the inductors core loss may increase significantly. both of these effects will degrade efficiency. the formula for peak inductor current is: i = i i 2 l(peak) load(max) l(max) + ? where: ? i = v 1 v v 5s l l(max) out out in(max) ? ? ? ? ? ? ? to maximize efficiency, 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 voltage (v ripple ) which is generated by ? i l x esr. therefore, esr must be equal or less than a maximum value calculated for a specified v ripple (typically less than 1% of the output volt- age) and ? i l(max) : esr = v i max ripple l(max) ? typically, capacitors in the range of 100 to 220 f 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 0 c. 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 flows 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 flows 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 regulator 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 sufficient 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 mic2178. a good design takes into consideration compo- nent placement and routing of power traces. the first thing to consider is the locations of the input capacitor, 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.
mic2178 micrel, inc. m9999-031805 12 march 2005 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 bias sgnd pwrgd comp pgnd fb sw vin c2 100 f 10v v out 3.3v/1a l1 50 h c4 6.8nf c3 0.01 f r3 10k mic2178 pwm skip mode pwm mode sync en r1 20k r2 10k v in 4.5v to 16.5v c1 22 f 35v u1 20 11 10 18 13 14C17 19 12 4C7 3,8 1,2,9 d1 mbrs130l u1 micrel mic2178-3.3bwm c1 avx tpse226m035r0300, esr = 0.3 ? c2 avx tpsd107m010r0100, esr = 0.1 ? c3 z5uorx7r ceramic dielectric material c4 x7rornp0 ceramic dielectric material d1 motorola mbrs130lt3 l1 coiltronics ctx50-4p, dcr = 0.097 ? l1 coilcraft do3316p-473, dcr = 0.12 ? l1 bi hm77-11003, dcr = 0.073 ? figure 1. mic2178 4.5vC16.5v to 3.3v/1a regulator bias sgnd pwrgd comp pgnd fb sw vin c2 100 f 10v v out 5v/1a l1 50 h c4 6.8nf c3 0.01 f r3 10k mic2178 pwm skip mode pwm mode sync en r1 20k r2 10k v in 5.4v to 16.5v c1 22 f 35v u1 20 11 10 18 13 14C17 19 12 4C7 3,8 1,2,9 d1 mbrs130l u1 micrel mic2178-5.0bwm c1 avx tpse226m035r0300, esr = 0.3 ? c2 avx tpsd107m010r0100, esr = 0.1 ? c3 z5uorx7r ceramic dielectric material c4 x7rornp0 ceramic dielectric material d1 motorola mbrs130lt3 l1 coiltronics ctx50-4p, dcr = 0.097 ? l1 coilcraft do3316p-473, dcr = 0.12 ? l1 bi hm77-11003, dcr = 0.073 ? figure 2. mic2178 5.4vC16.5v to 5v/1a regulator currents returning to the power supply ground bus. sgnd and pgnd should be tied together by a ground plane that extends under the mic2178.
march 2005 13 m9999-031805 mic2178 micrel, inc. bias sgnd pwrgd comp pgnd fb sw vin c2 68 f 20v v out 12v/1a l1 68 h c4 6.8nf c3 0.01 f mic2178 pwm skip mode pwm mode sync r2 174k 1% r1 20k 1% en r1 20k r2 10k v in 12.5v to 16.5v c1 22 f 35v u1 20 11 10 18 13 14C17 19 12 4C7 3,8 1,2,9 d1 mbrs130l u1 micrel mic2178bwm c1 avx tpse226m035r0300, esr = 0.3 ? c2 avx tpse686m020r0150, esr = 0.15 ? c3 z5uorx7r ceramic dielectric material c4 x7rornp0 ceramic dielectric material d1 motorola mbrs130lt3 l1 coiltronics ctx68-4p, dcr = 0.238 ? l1 coilcraft do3316p-683, dcr = 0.016 ? l1 bi hm77-11003, dcr = 0.233 ? r3 10k figure 3. mic2178 12.5vC16.5v to 12v/1a regulator bias sgnd pwrgd comp pgnd fb sw vin c2 220 f 10v x2 v out 3.3v/2.5a l1 33 h c4 6.8nf c3 0.01 f mic2178 pwm skip mode pwm mode sync en r1 20k r2 10k v in 10v to 16.5v c1 22 f 35v x2 u1 20 11 10 18 13 14C17 19 12 4C7 3,8 1,2,9 d1 mbrs130l u1 micrel mic2178-3.3bwm c1 avx tpse226m035r0300, esr = 0.3 ? c2 avx tpse227m010r0100, esr = 0.1 ? c3 z5uorx7r ceramic dielectric material c4 x7rornp0 ceramic dielectric material d1 motorola mbrs130lt3 l1 bi hm77-18004, dcr = 0.075 ? r3 10k figure 4. mic2178 10vC16.5v to 3.3v/2.5a regulator bias sgnd pwrgd comp pgnd fb sw vin c2 100 f 10v v out 3.3v/1a l1 33 h c4 6.8nf c3 0.01 f mic2178 pwm skip mode pwm mode sync en r1 20k r2 10k v in 4.5v to 10v c1 22 f 35v u1 20 11 10 18 13 14C17 19 12 4C7 3,8 1,2,9 d1 mbrs130l u1 micrel mic2178-3.3bwm c1 avx tpse226m035r0300, esr = 0.3 ? c2 avx tpsd107m010r0100, esr = 0.1 ? c3 z5uorx7r ceramic dielectric material c4 x7rornp0 ceramic dielectric material d1 motorola mbrs130lt3 l1 coiltronics ctx33-3p, dcr = 0.077 ? l1 coilcraft do3316-333, dcr = 0.088 ? l1 bi hm77-60002, dcr = 0.035 ? r3 10k figure 5. mic2178 4.5vC10v to 3.3v/1a regulator
mic2178 micrel, inc. m9999-031805 14 march 2005 bias sgnd pwrgd comp pgnd fb sw vin c2 100 f 10v v out 3.3v/1a l1 50 h c4 6.8nf c3 0.01 f mic2178 pwm skip mode pwm mode sync en r1 20k r2 10k v in 4.5v to 16.5v c1 22 f 35v u1 20 11 10 18 13 14C17 19 12 4C7 3,8 1,2,9 d1 mbrs130l u1 micrel mic2178-3.3bwm c1 avx tpse226m035r0300, esr = 0.3 ? c2 avx tpsd107m010r0100, esr = 0.1 ? c3 z5uorx7r ceramic dielectric material c4 x7rornp0 ceramic dielectric material d1 motorola mbrs130lt3 q1 siliconix si9435dy pmos l1 coiltronics ctx50-4p, dcr = 0.097 ? l1 coilcraft do3316-473, dcr = 0.12 ? l1 bi hm77-11003, dcr = 0.073 ? g q1 si9435 s d c3 0.01 f figure 6. mic2178 reversed battery protected regulator bias sgnd pwrgd comp pgnd fb sw vin c2 100 f 10v +v out / +i out 5v/0.5a c6 6.8nf c5 0.01 f mic2178 pwm skip mode pwm mode sync en r1 20k r2 10k v in 8v to 16.5v c1 22 f 35v u1 20 11 10 18 13 14C17 19 12 4C7 3,8 1,2,9 d1 mbrs130l u1 micrel mic2178-5.0bwm c1 avx tpse226m035r0300, esr = 0.3 ? c2 avx tpsd107m010r0100, esr = 0.1 ? c3 avx tpsd107m010r0100, esr = 0.1 ? c4 avx tpsd107m010r0100, esr = 0.1 ? c5 z5uorx7r ceramic dielectric material c6 x7rornp0 ceramic dielectric material d1 motorola mbrs130lt3 d2 motorola mbrs130lt3 l1 coiltronics ctx50-4p, dcr = 0.097 ? c4 100 f 10v t1 50 h 2 1 4 3 d2 mbrs130l c2 100 f 10v Cv out /-i out C5v/0.5a +i out + (Ci out ) 1a dc = + v out v in dc 40% then C i out +i out dc 40% then C i out +i out (1C dc) r3 10k figure 7. mic2178 8vC16.5v to 5v/500ma regulator
march 2005 15 m9999-031805 mic2178 micrel, inc. 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 rectifier 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 package information 0.022 (0.559) 0.018 (0.457) 5 typ 0.408 (10.363) 0.404 (10.262) 0.509 (12.929) 0.505 (12.827) 0.103 (2.616) 0.099 (2.515) seating plane 0.027 (0.686) 0.031 (0.787) 0.016 (0.046) typ 0.301 (7.645) 0.297 (7.544) 0.094 (2.388) 0.090 (2.286) 0.297 (7.544) 0.293 (7.442) 10 typ 0.032 (0.813) typ 0.330 (8.382) 0.326 (8.280) 7 typ 0.050 (1.270) typ 0.015 (0.381) r 0.015 (0.381) min pin 1 dimensions: inches (mm) 20-lead wide sop (wm) micrel inc. 2180 fortune drive san jose, ca 95131 usa tel + 1 (408) 944-0800 fax + 1 (408) 474-1000 web http://www.micrel.com this information furnished by micrel in this data sheet is believed to be accurate and reliable. however no responsibility is a ssumed by micrel for its use. micrel reserves the right to change circuitry and specifications at any time without notification to the customer. micrel products are not designed or authorized for use as components in life support appliances, devices or systems where malfu nction of a product can reasonably be expected to result in personal injury. life support devices or systems are devices or systems that (a) are intend ed 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 significant inj ury to the user. a purchasers use or sale of micrel products for use in life support appliances, devices or systems is a purchasers own risk and purchaser a grees to fully indemnify micrel for any damages resulting from such use or sale. ? 2001 micrel incorporated

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