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mic2207 3mm x 3mm 2mhz 3a pwm buck regulator mlf and micro leadframe are registered trademarks of amkor technology, inc. micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel +1 ( 408 ) 944-0800 ? fax + 1 (408) 474-1000 ? http://www.micrel.com general description the micrel mic2207 is a high-efficiency pwm buck (step- down) regulators that provides up to 3a of output current. the mic2207 operates at 2mhz and has proprietary internal compensation that allows a closed loop bandwidth of over 200khz. the low on-resistance internal p-channel mosfet of the mic2207 allows efficiencies over 94%, reduces external components count and eliminates the need for an expensive current sense resistor. the mic2207 operates from 2.7v to 5.5v input and the output can be adjusted down to 1v. the devices can operate with a maximum duty cy cle of 100% for use in low- dropout conditions. the mic2207 is available in the exposed pad 12-pin 3mm x 3mm mlf ? package with a junction operating range from ?40c to +125c. data sheets and support documentation can be found on micrel?s web site at: www.micrel.com . features ? 2.7 to 5.5v supply voltage ? 2mhz pwm mode ? output current to 3a ? >94% efficiency ? 100% maximum duty cycle ? adjustable output voltage option down to 1v ? ultra-fast transient response ? ultra-small external components stable with a 1h inductor and a 4.7f output capacitor ? fully integrated 3a mosfet switch ? micropower shutdown ? thermal shutdown and current limit protection ? pb-free 12-pin 3mm x 3mm mlf ? package ? ?40 c to +125 c junction temperature range applications ? 5v or 3.3v point of load conversion ? telecom/networking equipment ? set top boxes ? storage equipment ? video cards ? ddr power supply typical application mic2207 3a 2mhz buck regulator 80 82 84 86 88 90 92 94 96 00.511.522.53 efficiency (%) output current (a) mic2207 3.3v out efficiency 4.5v in 5v in 5.5v in april 2010 m9999-041910
micrel, inc. mic2207 april 2010 2 m9999-041910 ordering information part number output voltage (1) junction temp. range package lead finish MIC2207YML adj. ?40 to +125c 12-pin 3mm x 3mm mlf ? pb-free note: 1. other voltage options available. contact micrel for details. pin configuration bias en sw vin pgnd sgnd sw vin pgnd pgood 5 1 2 3 4 8 fb nc 67 12 11 10 9 ep 12-pin 3mm x 3mm mlf ? (ml) pin description pin number pin name pin function 1,12 sw switch (output): internal po wer p-channel mosfet output switch 2,11 vin supply voltage (input): supply voltage for the source of the internal p-channel mosfet and driver. requires bypass capacitor to gnd. 3,10 pgnd power ground. provides the ground return path for the high-side drive current. 4 sgnd signal (analog) ground. provides return path for control circuitry and internal reference. 5 bias internal circuit bias supply. must be bypassed with a 0.1f ceramic capacitor to sgnd. 6 fb feedback. input to the error amplifier, c onnect to the external resistor divider network to set the output voltage. 7 nc no connect. not internally connected to die. this pin can be tied to any other pin if desired. 8 en enable (input). logic level low will shutdown the device, reducing the current draw to less than 5a. 9 pgood power good. open drain output that is pulled to ground when the output voltage is within 7.5% of the set regulation voltage ep gnd connect to ground.
micrel, inc. mic2207 april 2010 3 m9999-041910 absolute maximum ratings (1) supply voltage (v in ) .......................................................+6v output switch voltage (v sw ) ..........................................+6v output switch current (i sw )............................................11a logic input voltage (v en ) .................................. ?0.3v to v in storage temperature (t s ) .........................?60c to +150c esd rating (3) .................................................................. 2kv operating ratings (2) supply voltage (v in )..................................... +2.7v to +5.5v logic input voltage (v en ) ....................................... 0v to v in junction temperature (t j ) ........................ ?40c to +125c junction thermal resistance 3x3 mlf-12l ( ja ) .............................................60c/w electrical characteristics (4) v in = v en = 3.6v; l = 1h; c out = 4.7f; t a = 25c, unless noted. bold values indicate ?40c t j +125c. parameter condition min typ max units supply voltage range 2.7 5.5 v under-voltage lockout threshold (turn-on) 2.45 2.55 2.65 v uvlo hysteresis 100 mv quiescent current v fb = 0.9 * vnom (not switching) 570 900 a shutdown current v en = 0v 2 10 a [adjustable] feedback voltage 1% i load = 100ma 2% (over temperature) i load = 100ma 0.99 0.98 1 1.01 1.02 v fb pin input current 1 na current limit in pwm mode v fb = 0.9 * v nom 3.5 5 a output voltage line regulation v out > 2v; v in = v out + 500mv to 5.5v; i load = 100ma v out < 2v; v in = 2.7v to 5.5v; i load = 100ma 0.07 % output voltage load regulation 20ma < i load < 3a 0.2 0.5 % maximum duty cycle v fb 0.4v 100 % pwm switch on-resistance i sw = 50ma; v fb = 0.7v fb_nom (high side switch) 95 200 300 m? oscillator frequency 1.8 2 2.2 mhz enable threshold 0.5 0.85 1.3 v enable hysteresis 50 mv enable input current 0.1 2 a power good range 7 10 % power good resistance i pgood = 500a 145 250 ? over-temperature shutdown 160 c over-temperature hysteresis 20 c notes: 1. exceeding the absolute maximum rating may damage the device. 2. the device is not guaranteed to function outside its operating rating. 3. devices are esd sensitive. hand ling precautions recommended. human body model, 1.5k in series with 100pf. 4. specification for packaged product only. 5. dropout voltage is defined as the input-to-output differentia l at which the output voltage drops 2% below its nominal value that is initially measured at a 1v differential. for outputs below 2.7v, the dropout voltage is the input-to-output voltage differential with a minimum input voltage of 2.7v.
micrel, inc. mic2207 april 2010 4 m9999-041910 typical characteristics 80 82 84 86 88 90 92 94 96 00.511.522.53 efficiency (%) output current (a) mic2207 3.3v out efficiency 4.5v in 5v in 5.5v in 80 82 84 86 88 90 92 94 96 98 100 00.511.522.53 efficiency (%) output current (a) mic2207 2.5v out efficiency 3.3v in 3v in 3.6v in 80 82 84 86 88 90 92 94 00.511.522.53 efficiency (%) output current (a) mic2207 2.5v out efficiency 5.5v in 5v in 4.5v in 75 77 79 81 83 85 87 89 91 93 95 00.511.522.53 efficiency (%) output current (a) mic2207 1.8v out efficiency 3.6v in 3v in 3.3v in 70 72 74 76 78 80 82 84 86 88 90 00.511.522.53 efficiency (%) output current (a) mic2207 1.8v out efficiency 5.5v in 5v in 4.5v in 70 75 80 85 90 95 00.511.522.53 efficiency (%) output current (a) mic2207 1.5v out efficiency 3.6v in 3v in 3.3v in 65 67 69 71 73 75 77 79 81 83 85 00.511.522.53 efficiency (%) output current (a) mic2207 1.5v out efficiency 5.5v in 5v in 4.5v in 70 72 74 76 78 80 82 84 86 88 90 00.511.522.53 efficiency (%) output current (a) mic2207 1.2v out efficiency 3.6v in 3v in 3.3v in 65 67 69 71 73 75 77 79 81 83 85 00.511.522.53 efficiency (%) output current (a) mic2207 1.2v out efficiency 5.5v in 5v in 4.5v in 65 67 69 71 73 75 77 79 81 83 85 00.511.522.53 efficiency (%) output current (a) mic2207 1v out efficiency 3.6v in 3v in 3.3v in 60 65 70 75 80 85 00.511.522.53 efficiency (%) output current (a) mic2207 1v out efficiency 5.5v in 5v in 4.5v in 0.990 0.995 1.000 1.005 1.010 00.511.522.53 output voltage (v) output current (a) load regulation v in = 3.3v
micrel, inc. mic2207 april 2010 5 m9999-041910 typical characteristics (cont.) supply voltage (v) 0.990 0.992 0.994 0.996 0.998 1.000 1.002 1.004 1.006 1.008 1.010 -40 -20 0 20 40 60 80 100 120 feedback voltage (v) temperature (c) feedback voltage vs. temperature v in = 3.3v 1.500 1.600 1.700 1.800 1.900 2.000 2.100 2.200 2.300 2.400 2.500 -40 -20 0 20 40 60 80 100 120 frequency (mhz) temperature (c) frequency vs. temperature v in = 3.3v 0 0.2 0.4 0.6 0.8 1 1.2 012345 feedback voltage (v) supply voltage (v) feedback voltage vs. supply voltage v en = v in 0 100 200 300 400 500 600 700 800 900 012345 quiescent current (a) supply voltage (v) quiescent current vs. supply voltage v en = v in 70 75 80 85 90 95 100 105 110 115 120 2.73.23.74.24.75.2 p-channel r dson (mohm) supply voltage (v) r dson vs. supply voltage 0 20 40 60 80 100 120 140 160 -40 -20 0 20 40 60 80 100 120 p-channel r dson (mohm) temperature (c) r dson vs. temperature 3.3v in 0 0.2 0.4 0.6 0.8 1.0 1.2 2.7 3.2 3.7 4.2 4.7 enable threshold (v) supply voltage (v) enable threshold vs. supply voltage 0 0.2 0.4 0.6 0.8 1.0 1.2 -40 -20 0 20 40 60 80 100 120 enable threshold (v) temperature (c) enable threshold vs. temperature 3.3v in
micrel, inc. mic2207 april 2010 6 m9999-041910 functional characteristics continuious current time (200ns/di v.) switch vo ltage (2v/div.) inductor curren t (500ma/di v. ) v in = 3.3v v out = 1v l = 1h c out = 4.7f i out = 1a 0a discontinuous current time (200ns/di v.) switch vo ltage (2v/div.) inductor curren t (200ma/di v. ) v in = 3.3v v out = 1v l = 1h c out = 4.7f i out = 30ma 0a load transient response time (400s/di v.) output voltage (20mv/div.) output curren t (2a/div.) v in = 3.3v v out = 1.8v 0a output ripple time (400ns/di v.) switch vo ltage (2v/div.) output voltage (10mv/div.) ac coupled i out = 3.0a start-up waveforms time (40s/di v.) enable vo ltage (2v/div.) inductor curren t (2a/div.) input curren t (1a/div.) feedback vo ltage (1v/div.)
micrel, inc. mic2207 april 2010 7 m9999-041910 functional diagram vin vin bias en sw sw fb pgood pgnd enable and control logic pwm control p-channel current limit sgnd 1.0v 1.0v soft start bias, uvlo, thermal shutdown hsd ea mic2207 block diagram
micrel, inc. mic2207 april 2010 8 m9999-041910 pin descriptions vin two pins for vin provide power to the source of the internal p-channel mosfet along with the current limiting sensing. the vin operating voltage range is from 2.7v to 5.5v. due to the high switching speeds, a 10f capacitor is recommended close to vin and the power ground (pgnd) for each pin for bypassing. please refer to layout recommendations. bias the bias (bias) provides power to the internal reference and control sections of the mic2207. a 10 ? resistor from vin to bias and a 0.1f from bias to sgnd is required for clean operation. en the enable pin provides a logic level control of the output. in the off state, suppl y current of the device is greatly reduced (typically <1a). do not drive the enable pin above the supply voltage. fb the feedback pin (fb) provides the control path to control the output. for adjustable versions, a resistor divider connecting the feedback to the output is used to adjust the desired output voltage. the output voltage is calculated as follows: ? ? ? ? ? ? += 1 r2 r1 vv ref out where v ref is equal to 1.0v. a feedforward capacitor is recommended for most designs using the adjustable output voltage option. to reduce current draw, a 10k feedback resistor is recommended from the output to the fb pin (r1). also, a feedforward capacitor should be connected between the output and feedback (across r1 ). the large resistor value and the parasitic capacitance of the fb pin can cause a high frequency pole that can reduce the overall system phase margin. by placing a feedforward capacitor, these effects can be significantly reduced. feedforward capacitance (c ff ) can be calculated as follows: 200khz r12 1 c ff = sw the switch (sw) pin connects directly to the inductor and provides the switching current necessary to operate in pwm mode. due to the high speed switching on this pin, the switch node should be routed away from sensitive nodes. this pin also connects to the cathode of the free-wheeling diode. pgood power good is an open drain pull down that indicates when the output voltage has reached regulation. for a power good low, the output voltage is within 10% of the set regulation voltage. for output voltages greater or less than 10%, the pgood pin is high. this should be connected to the input supply through a pull up resistor. a delay can be added by placing a capacitor from pgood to ground. pgnd power ground (pgnd) is the ground path for the mosfet drive current. the current loop for the power ground should be as small as possible and separate from the signal ground (sgnd) loop. refer to the layout considerations fro more details. sgnd signal ground (sgnd) is the ground path for the biasing and control circuitry. the current loop for the signal ground should be separate from the power ground (pgnd) loop. refer to the lay out considerations for more details.
micrel, inc. mic2207 april 2010 9 m9999-041910 application information the mic2207 is a 3a pwm non-synchronous buck regulator. by switching an input voltage supply, and filtering the switched voltage through an inductor and capacitor, a regulated dc voltage is obtained. figure 1 shows a simplified example of a non-synchronous buck converter. figure 1. for a non-synchronous buck converter, there are two modes of operation; continuous and discontinuous. continuous or discontinuous refer to the inductor current. if current is continuously flowing through the inductor throughout the switching cycle, it is in continuous operation. if the inductor current drops to zero during the off time, it is in discontinuous operation. critically continuous is the point where any decrease in output current will cause it to enter discontinuous operation. the critically co ntinuous load current can be calculated as follows; l mhz vin v v v out out out ? ? ? ? ? ? ? ? ? = 22 2 continuous or discontinuous operation determines how we calculate peak inductor current. continuous operation figure 2 illustrates the switch voltage and inductor current during continuous operation. figure 2. continuous operation the output voltage is regulated by pulse width modulating (pwm) the switch voltage to the average required output voltage. the switching can be broken up into two cycles; on and off. during the on-time, the high side switch is turned on, current flows from the input supply through the inductor and to the output. the inductor current is figure 3. on-time charged at the rate; ( ) l vv out in ? to determine the total on-time, or time at which the inductor charges, the duty cycle needs to be calculated. the duty cycle can be calculated as; in out v v d = and the on time is; 2mhz d t on = therefore, peak to peak ripple current is; () l2mhz v v vv i in out outin pkpk ? = ? since the average peak to peak current is equal to the load current. the actual peak (or highest current the inductor will see in a steady state condition) is equal to the output current plus ? the peak to peak current. () l2mhz2 v v vv ii in out out in out pk ? += figure 4 demonstrates the off-time. during the off- time, the high-side internal p-channel mosfet turns off. since the current in the inductor has to discharge, the current flows through the free-wheeling schottky diode to the output. in this case, the inductor discharge rate is (where v d is the diode forward voltage);
micrel, inc. mic2207 april 2010 10 m9999-041910 () l vv d out + ? the total off time can be calculated as; 2mhz d1 t off ? = figure 4. off-time discontinuous operation discontinuous operation is when the inductor current discharges to zero during the off cycle. figure 5. demonstrates the switch voltage and inductor currents during discontinuous operation. figure 5. discontinuous operation when the inductor current (i l ) has completely discharged, the voltage on the switch node rings at the frequency determined by the parasitic capacitance and the inductor value. in figure 5, it is drawn as a dc voltage, but to see actual operation (with ringing) refer to the functional characteristics. discontinuous mode of operation has the advantage over full pwm in that at light loads, the mic2207 will skip pulses as necessary, redu cing gate drive losses, drastically improving light load efficiency. efficiency considerations calculating the efficiency is as simple as measuring power out and dividing it by the power in; 100 p p efficiency in out = where input power (p in ) is; ininin ivp = and output power (p out ) is calculated as; out out out ivp = the efficiency of the mic2207 is determined by several factors. ? rdson (internal p-channel resistance) ? diode conduction losses ? inductor conduction losses ? switching losses rdson losses are caused by the current flowing through the high side p-channel mosfet. the amount of power loss can be approximated by; dirp 2 out dson sw = where d is the duty cycle. since the mic2207 uses an internal p-channel mosfet, rdson losses are inversely proportional to supply voltage. higher supply voltage yields a higher gate to source voltage, reducing the rdson, reducing the mosfet conduction losses. a graph showing typical rdson vs input supply voltage can be found in the typical characteristics section of this datasheet. diode conduction losses occur due to the forward voltage drop (v f ) and the output current. diode power losses can be approximated as follows; () d1ivp outfd ? = for this reason, the schottky diode is the rectifier of choice. using the lowest forward voltage drop will help reduce diode conduction losses, and improve efficiency. duty cycle, or the ratio of output voltage to input voltage, determines whether the dominant factor in conduction losses will be the internal mosfet or the schottky diode. higher duty cycles place the power losses on the high side switch, and lower duty cycles place the power losses on the schottky diode. inductor conduction losses (p l ) can be calculated by multiplying the dc resistance (dcr) times the square of the output current; 2 out l idcrp =
micrel, inc. mic2207 april 2010 11 m9999-041910 also, be aware that there are additional core losses associated with switching current in an inductor. since most inductor manufacturers do not give data on the type of material used, approximating core losses becomes very difficult, so verify inductor temperature rise. switching losses occur twice each cycle , when the switch turns on and when the switch turns off. this is caused by a non-ideal world where switching transitions are not instantaneous, and neither are currents. figure 6 demonstrates (or exaggerates?) how switching losses due to the transitions dissipate power in the switch. figure 6. switching transition losses normally, when the switch is on, the voltage across the switch is low (virtually zero) and the current through the switch is high. this equates to low power dissipation. when the switch is off, voltage across the switch is high and the current is zero, again with power dissipation being low. during the transitions, the voltage across the switch (v s-d ) and the current through the switch (i s-d ) are at midpoint of their excursions and cause the transition to be the highest instantaneous power point. during continuous mode, these losses are the highest. also, with higher load currents, these losses are higher. for discontinuous operation, the transition losses only occur during the ?off? transition since the ?on? transitions there is no current flow through the inductor. component selection input capacitor a 10f ceramic is recommended on each vin pin for bypassing. x5r or x7r dielectrics are recommended for the input capacitor. y5v dielectrics lose most of their capacitance over temperature and are therefore not recommended. also, tantalum and electrolytic capacitors alone are not recommended because of their reduced rms current handling, reliability, and esr increases. an additional 0.1f is recommended close to the vin and pgnd pins for high frequency filtering. smaller case size capacitors are recommended due to their lower esr and esl. please refer to layout recommendations for proper layout of the input capacitor. output capacitor the mic2207 is designed for a 4.7f output capacitor. x5r or x7r dielectrics are recommended for the output capacitor. y5v dielectrics lose most of their capacitance over temperature and are therefore not recommended. in addition to a 4.7f, a small 0.1f is recommended close to the load for high frequency filtering. smaller case size capacitors are recommended due to their lower equivalent series esr and esl. the mic2207 utilizes type iii voltage mode internal compensation and utilizes an internal zero to compensate for the double pole roll off of the lc filter. for this reason, larger output capacitors can create instabilities. in cases where a 4.7f output capacitor is not sufficient, the mic2208 offers the ability to externally control the compensation, allowing for a wide range of output capacitor types and values. inductor selection the mic2207 is designed for use with a 1h inductor. proper selection should ensure the inductor can handle the maximum average and peak currents required by the load. maximum current ratings of the inductor are generally given in two methods; permissible dc current and saturation current. permissible dc current can be rated either for a 40c temperature rise or a 10% to 20% loss in inductance. ensure the inductor selected can handle the maximum operating current. when saturation current is specified, make sure that there is enough margin that the peak current will not saturate the inductor. diode selection since the mic2207 is non-synchronous, a free-wheeling diode is required for proper operation. a schottky diode is recommended due to the low forward voltage drop and their fast reverse recovery time. the diode should be rated to be able to handle the average output current. also, the reverse voltage rating of the diode should exceed the maximum input voltage. the lower the forward voltage drop of the diode the better the efficiency. please refer to the layout recommendations to minimize switching noise. feedback resistors the feedback resistor set the output voltage by dividing down the output and sending it to the feedback pin. the feedback voltage is 1.0v. calculating the set output voltage is as follows; ? ? ? ? ? ? + = 1 r2 r1 vv fb out where r1 is the resistor from vout to fb and r2 is the resistor from fb to gnd. the recommended feedback resistor values for common output voltages are available
micrel, inc. mic2207 april 2010 12 m9999-041910 in the bill of materials on page 19. although the range of resistance for the fb resistors is very wide, r1 is recommended to be 10k. this minimizes the effect the parasitic capacitance of the fb node. feedforward capacitor (c ff ) a capacitor across the resistor from the output to the feedback pin (r1) is recommended for most designs. this capacitor can give a boost to phase margin and increase the bandwidth for transient response. also, large values of feedforward capacitance can slow down the turn-on characteristics, reducing inrush current. for maximum phase boost, c ff can be calculated as follows; r1 200khz 2 1 c ff = bias filter a small 10 ? resistor is recommended from the input supply to the bias pin along with a small 0.1f ceramic capacitor from bias to ground. this will bypass the high frequency noise generated by the violent switching of high currents from reaching the internal reference and control circuitry. tantalum and electrolytic capacitors are not recommended for the bias, these types of capacitors lose their ability to filter at high frequencies. loop stability and bode analysis bode analysis is an excellent way to measure small signal stability and loop response in power supply designs. bode analysis monitors gain and phase of a control loop. this is done by breaking the feedback loop and injecting a signal into the feedback node and comparing the injected signal to the output signal of the control loop. this will require a network analyzer to sweep the frequency and compare the injected signal to the output signal. the most common method of injection is the use of a transformer. figure 7 demonstrates how a transformer is used to inject a signal into the feedback network. figure 7. transformer injection a 50 ? resistor allows impedance matching from the network analyzer source. this method allows the dc loop to maintain regulation and allow the network analyzer to insert an ac signal on top of the dc voltage. the network analyzer will then sweep the source while monitoring a and r for an a/r measurement. while this is the most common method for measuring the gain and phase of a power supply, it does have significant limitations. first, to measure low frequency gain and phase, the transformer needs to be high in inductance. this makes frequencies <100hz require an extremely large and expensive transformer. conversely, it must be able to inject high frequencies. transformers with these wide frequency ranges generally need to be custom made and are extremely expensive (usually to the tune of several hundred dollars!). by using an op-amp, cost and frequency limitations caused by an injection transformer are completely eliminated. figure 8 demonstrates using an op-amp in a summing amplifier configuration for signal injection. network analyzer source +8v r1 1k r3 1k r4 1k 50 feedback output network analyzer ?a? input network analyzer ?r? input mic922bc5 figure 8. op amp injection r1 and r2 reduce the dc voltage from the output to the non-inverting input by half. the network analyzer is generally a 50 ? source. r1 and r2 also divide the ac signal sourced by the network analyzer by half. these two signals are ?summed? together at half of their original input. the output is then amplified by 2 by r3 and r4 (the 50 ? is to balance the network analyzer?s source impedance) and sent to the feedback signal. this essentially breaks the loop and injects the ac signal on top of the dc output voltage and sends it to the feedback. by monitoring the feedback ?r? and output ?a?, gain and phase are measured. this method has no minimum frequency. ensure that the bandwidth of the op-amp being used is much greater than the expected bandwidth of the power supply?s control loop. an op-amp with >100mhz bandwidth is more than sufficient for most power supplies (which includes both linear and switching) and are more common and significantly cheaper than the injection transformers previously mentioned. the one disadvantage to using the op-amp injection method, is the supply voltages need to be below the maximum operating voltage of the op-amp. also, the maximum output voltage for driving 50 ? inputs using the mic922 is 3v. for measuring higher output voltages, a 1m ? input impedance is required for the a and r channels. remember to always measure the
micrel, inc. mic2207 april 2010 13 m9999-041910 output voltage with an oscilloscope to ensure the measurement is working properly. you should see a single sweeping sinusoidal waveform without distortion on the output. if there is distortion of the sinusoid, reduce the amplitude of the source signal. you could be overdriving the feedback causing a large signal response. the following bode analysis show the small signal loop stability of the mic2207. the mic2207 utilizes a type iii compensation. this is a dominant low frequency pole, followed by 2 zero?s and finally the double pole of the inductor capacitor filter, creating a final 20db/decade roll off. bode analysis gives us a few important data points; speed of response (gain bandwidth or gbw) and loop stability. loop speed or gbw determines the response time to a load transient. faster response times yield smaller voltage deviations to load steps. instability in a control loop occurs when there is gain and positive feedback. phase margin is the measure of how stable the given system is. it is measured by determining how far the phase is from crossing zero when the gain is equal to 1 (0db). -30 -20 -10 0 10 20 30 40 50 60 gain (db) frequency (hz) bode plot v in =3.3v, v out =1.8v, i out =3a -105 -70 -35 0 35 70 105 140 175 210 phase () 100 1k 10k 100k 1m l=1h c out = 4.7f r1 = 10k r2 = 12.4k c ff = 82pf gain phase typically for 3.3vin and 1.8vout at 3a; ? phase margin=47 degrees ? gbw=156khz gain will also increase with input voltage. the following graph shows the increase in gbw for an increase in supply voltage. -30 -20 -10 0 10 20 30 40 50 60 gain (db) frequency (hz) bode plot v in =5v, v out =1.8v, i out =3a -105 -70 -35 0 35 70 105 140 175 210 phase () 100 1k 10k 100k 1m l=1h c out = 4.7f r1 = 10k r2 = 12.4k c ff = 82pf gain phase 5vin, 1.8vout at 3a load; ? phase margin=43.1 degrees ? gbw= 218khz being that the mic2207 is non-synchronous; the regulator only has the ability to source current. this means that the regulator has to rely on the load to be able to sink current. this causes a non-linear response at light loads. the following plot shows the effects of the pole created by the nonlinearity of the output drive during light load (discontinuous) conditions. -30 -20 -10 0 10 20 30 40 50 60 gain (db) frequency (hz) bode plot v in =3.3v,v out =1.8v,i out =50ma -105 -70 -35 0 35 70 105 140 175 210 phase () 100 1k 10k 100k 1m l=1h c out = 4.7f r1 = 10k r2 = 12.4k c ff = 82pf gain phase 3.3vin, 1.8vout iout=50ma; ? phase margin=90.5 degrees ? gbw= 64.4khz feed forward capacitor the feedback resistors are a gain reduction block in the overall system response of the regulator. by placing a capacitor from the output to the feedback pin, high frequency signal can bypass the resistor divider, causing a gain increase up to unity gain. -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 gain (db) frequency (hz) gain and phase vs. frequency 0 5 10 15 20 25 phase boost () 100 1k 10k 100k 1m l=1h c out = 4.7f r1 = 10k r2 = 12.4k c ff = 82pf gain phase the graph above shows the effects on the gain and phase of the system caused by feedback resistors and a feedforward capacitor. the maximum amount of phase boost achievable with a feedforward capacitor is graphed below.
micrel, inc. mic2207 april 2010 14 m9999-041910 0 5 10 15 20 25 30 35 40 45 50 12345 pahse boost () output voltage (v) max. amount of phase boost obtainable using c ff vs. output voltage v ref = 1v by looking at the graph, phase margin can be affected to a greater degree with higher output voltages. the next bode plot shows the phase margin of a 1.8v output at 3a without a feedforward capacitor. -30 -20 -10 0 10 20 30 40 50 60 gain (db) frequency (hz) bode plot v in =3.3v, v out =1.8v, i out =3a -105 -70 -35 0 35 70 105 140 175 210 phase () 100 1k 10k 100k 1m l=1h c out = 4.7f r1 = 10k r2 = 12.4k c ff = 0pf gain phase as you can see the typical phase margin, using the same resistor values as before without a feedforward capacitor results in 33.6 degrees of phase margin. our prior measurement with a feedforward capacitor yielded a phase margin of 47 degrees. the feedforward capacitor has given us a phase boost of 13.4 degrees (47 degrees ? 33.6 degrees = 13.4 degrees). output impedance and transient response output impedance, simply stated, is the amount of output voltage deviation vs. the load current deviation. the lower the output impedance, the better. out out out i v z = output impedance for a buck regulator is the parallel impedance of the output capacitor and the mosfet and inductor divided by the gain; cout l dson total x gain xdcr r z ++ = to measure output impedance vs. frequency, the load current must be swept across the frequencies measured, while the output voltage is m onitored. fig 9 shows a test set-up to measure output impedance from 10hz to 1mhz using the mic5190 high speed controller. by setting up a network analyzer to sweep the feedback current, while monitoring the output of the voltage regulator and the voltage across the load resistance, output impedance is easily obtainable. to keep the current from being too high, a dc offset needs to be applied to the network analyzer?s source signal. this can be done with an external supply and 50 ? resistor. make sure that the currents are verified with an oscilloscope first, to ensure the integrity of the signal measurement. it is always a good idea to monitor the a and r measurements with a scope while you are sweeping it. to convert the network analyzer data from dbm to something more useful (such as peak to peak voltage and current in our case); 707.0 250 ? 1mw 10 v 10 dbm = and peak to peak current; load 10 dbm r707.0 250 ? 1mw 10 i = the following graph shows output impedance vs frequency at 2a load current sweeping the ac current from 10hz to 10mhz, at 1a peak to peak amplitude. 0.001 0.01 0.1 1 output impedance (ohms) frequency (hz) output impedance vs. frequency 100 1k 10k 100k 1m v out =1.8v l=1h c out =4.7f + 0.1 5v in 3.3vin 10 from this graph, you can see the effects of bandwidth and output capacitance. for frequencies <200khz, the output impedance is dominated by the gain and inductance. for frequencies >200khz, the output impedance is dominated by the capacitance. a good approximation for transient response can be calculated from determining the frequency of the load step in amps per second; 2 a/sec = f
micrel, inc. mic2207 april 2010 15 m9999-041910 ripple measurements to properly measure ripple on either input or output of a switching regulator, a proper ring in tip measurement is required. standard oscilloscope probes come with a grounding clip, or a long wire with an alligator clip. unfortunately, for high frequency measurements, this ground clip can pick-up high frequency noise and erroneously inject it into the measured output ripple. the standard evaluation board accommodates a home made version by providing probe points for both the input and output supplies and their respective grounds. this requires the removing of the oscilloscope probe sheath and ground clip from a standard oscilloscope probe and wrapping a non-shielded bus wire around the oscilloscope probe. if there does not happen to be any non shielded bus wire immediately available, the leads from axial resistors will work. by maintaining the shortest possible ground lengths on the oscilloscope probe, true ripple measurements figure 9. output impedance measurement then, determine the output impedance by looking at the output impedance vs frequen cy graph. next, calculate the voltage deviation times the load step; out out out ziv = the output impedance graph shows the relationship between supply voltage and output impedance. this is caused by the lower rdson of the high side mosfet and the increase in gain with increased supply voltages. this explains why higher supply voltages have better transient response. can be obtained. cout l dson total x gain xdcr r z ++ =
micrel, inc. mic2207 april 2010 16 m9999-041910 recommended layout / 3a evaluation board recommended top layout recommended bottom layout
micrel, inc. mic2207 april 2010 17 m9999-041910 mic2207 scheme and b.o.m for 3a output mic2207 schematic item part number description manufacturer qty c1a,c1b c2012jb0j106k grm219r60j106ke19 08056d106mat 10f ceramic capacitor x5r 0805 6.3v 10f ceramic capacitor x5r 0805 6.3v 10f ceramic capacitor x5r 0805 6.3v tdk murata avx 2 c2 0402zd104mat 0.1f ceramic capacitor x5r 0402 10v avx 1 c3 c2012jb0j475k grm188r60j475ke19 06036d475mat 4.7f ceramic capacitor x5r 0603 6.3v 4.7f ceramic capacitor x5r 0603 6.3v 4.7f ceramic capacitor x5r 0603 6.3v tdk murata avx 1 c4 vj0402a820kxaa 82pf ceramic capacitor 0402 vishay vt 1 d1 ssa33l 3a schottky 30v sma vishay semi 1 rlf7030-1r0n6r4 1h inductor 8.8m ? 7.1mm(l) x 6.8mm (w)x 3.2mm(h) tdk 1 744 778 9001 1h inductor 12m ? 7.3mm(l)x7.3mm(w)x3.2mm(h) wurth electronik 1 l1 ihlp2525ah-01 1 1h inductor 17.5m ? (l)6.47mmx(w)6.86mmx(h) 1.8mm vishay dale 1 r1,r4 crcw04021002f 10k ? 1% 0402 resistor vishay dale 1 r2 crcw04026651f crcw04021242f crcw04022002f crcw04024022f 6.65k ? 1% 0402 for 2.5v out 12.4k ? 1% 0402 for 1.8 v out 20k ? 1% 0402 for 1.5 v out 40.2k ? 1% 0402 for 1.2 v out open for 1.0 v out vishay dale vishay dale vishay dale vishay dale vishay dale 1 r3 crcw040210r0f 10 ? 1% 0402 resistor vishay dale 1 u1 MIC2207YML 2mhz 3a buck regulator micrel 1 notes: 1. sumida: www.sumida.com . 2. murata: www.murata.com . 3. vishay: www.vishay.com . 4. micrel, inc.: www.micrel.com .
micrel, inc. mic2207 april 2010 18 m9999-041910 package information 12-pin mlf ? (ml) 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 the information furnished by micrel in this data sheet is believ ed to be accurate and reliable. however, no responsibility is a ssumed by micrel for its use. micrel reserves the right to change circuitry and spe cifications at any time without notification to the customer. micrel products are not designed or author ized for use as components in life support app liances, devices or systems where malfu nction of a product reasonably be expected to result in personal injury. life s upport devices or systems are devices or systems that (a) are intended for surgical impla into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significan t 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. can nt ? 2005 micrel, incorporated.

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