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mic 4604 85v half bridge mosfet driver s with up to 16v programmable gate drive micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel +1 (408) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com june 25 , 2013 revision 1.0 general description the mic4604 is an 85v half bridge mosfet driver. the mic4604 features fast 39ns propagation delay times and 20ns driver rise/fall times for a 1nf capacitive load. the low - side and high - side gate drivers are independently control led. the mic4604 has ttl input thresholds. it includes a high - voltage internal diode that helps charge the high - side gate drive bootstrap capacitor. a robust, high - speed, and low - power level shifter provides clean level transitions to the high - side output. the ro bust operation of the mic4604 ensure s that the outputs are not affected by supply glitches, hs ringing below ground, or hs slewing with high - speed voltage transitions. undervoltage protection is provided on both the low - side and high - side drivers. the mic 4604 is available in a n 8 - pin soic package and a tiny 10 - pin 2.5mm 2.5mm tdfn package. both packages have an operating junction temperature range of ? 40 c to +125 c. datasheets and support documentation are available on micrel?s web site at: www.micrel.com . features ? 5.5v to 16v gate drive supply voltage range. ? drives high - side and low - side n - channel mosfets with independent inputs ? ttl input thresholds ? on chip bootstrap diode ? fast 39 ns propagation times ? drives 1000 pf load with 20ns rise and fall times ? low power consumption ? supplies under voltage protection ? ? 40c to +125c junction temperature range applications ? power i nverter s ? high - voltage step - down regulators ? half, f ull and 3 - phase bridge motor drives ? distributed p ower systems ? computing peripherals typical application motor door lock solution
micrel, inc. mic4604 june 25 , 2013 2 revision 1.0 ordering information part number part marking input junction temperature range package MIC4604YMt 463 ttl ? 40 to +125c 10- pin 2.5mm 2.5mm tdfn MIC4604YM mic4604 ym tt l ? 40 to +125c 8 - pin soic pin configuration s mic4604 ymt 10- pin 2.5mm x2.5mm tdfn (mt ) (top view) MIC4604YM 8 - pin soic (m) (top view) pin description pin number pin name pin function tdfn soic 1 1 vdd input supply for gate drivers. decouple this pin to vss with a >2.2 f capacitor. anode connection to internal bootstrap diode. 2 , 10 nc no connect 3 2 hb high - side bootstrap supply. external b ootstrap capacitor is required. connect bootstrap cap acitor across this pin and hs. cathode connect ion to internal bootstrap diode. 4 3 ho high - side drive output. connect to gate of the external high - side power mosfet. 5 4 hs high -s ide drive reference connection. connect to source of the external high - side power mosfet. connect this pin to the bootstr ap capacitor. 6 5 hi high - side drive input. 7 6 li low - side drive input. 8 7 vss driver reference supply input. connected to power ground of external circuitry and to source of low - side power mosfet. 9 8 lo low - side drive output. connect to gate of the external low - side power mosfet. ep epad exposed pad. connect to vss.
micrel, inc. mic4604 june 25 , 2013 3 revision 1.0 absolute maximum ratings ( 1 , 4 ) supply voltage (v dd , v hb ? v hs ) ..................... ? 0.3v to 18v input voltag es (v li, v hi , v en ) ................. ? 0.3v to v dd + 0.3v voltage on lo (v lo ) ............................. ? 0.3v to v dd + 0.3v voltage on ho (v ho ) ..................... v hs ? 0.3v to v hb + 0.3v voltage on hs (continuous) ............................... ? 1v to 90v voltage on hb .............................................................. 108v average current in vdd to hb diode ....................... 100ma storage temperature (t s ) ......................... ? 60c to +150c esd rating ( 3) hbm ...................................................................... 1.5kv mm ......................................................................... 200v operating ratings ( 2 ) supply voltage (v dd ) [decreasing v dd ] ........... 5.25v to 16v supply voltage (v dd ) [increasing v dd ] .............. 5.5v to 16v voltage on hs .................................................... ? 1v to 85v voltage on hs (repetitive transient) ................... ? 5v to 90v hs slew rate ............................................................ 50v/ns voltage on hb ................................ v hs + 4.5v to v hs + 16v and/or .......................................... v dd ? 1v to v dd + 85v junction temperature (t j ) ........................ ? 40c to +125c junction thermal resistance 2.5mm x 2.5mm t dfn - 10l ( ja ) ....................... 75 c/w soic - 8l ( ja ) .................................................. 98.9 c/w electrical characteristics ( 4 ) v dd = v hb = 12v; v ss = v hs = 0v; no load on lo or ho; t a = +25c; unless otherwise noted. bold values indicate ? 40c t j +125c symbol par ameter condition min. typ. max. units supply current i dd v dd quiescent current li = hi = 0v 48 200 a i ddo v dd operating current f = 20khz 136 300 a i hb total hb quiescent current li = hi = 0v or li = 0v and hi = 5v 20 75 a i hbo total hb opera ting current f = 20khz 29 200 a i hbs hb to v ss quiescent current v hs = v hb = 90v 0.5 5 a input (li, hi) v il low - level input voltage 0.8 v v ih high - level input voltage 2.2 v v hys input voltage hysteresis 0.05 v r i input pull - down resi stance 100 240 500 k undervoltage protection v ddf v dd falling threshold 4.0 4.4 4.9 v v ddh v dd threshold hysteresis rising v dd threshold; v ddr = v ddf + v ddh 0.21 v v hbf hb falling threshold 4.0 4.4 4.9 v v hbh hb threshold hysteresis ris ing v hb threshold; v hbr = v hbf + v hbh 0.23 v bootstrap diode v dl low - current forward voltage i vdd - hb = 100 a 0.42 0.70 v v dh high - current forward voltage i vdd - hb = 50m a 0.75 1.0 v r d dynamic resistance i vdd - hb = 50m a 2.8 5.0 notes: 1. exceed ing the absolute maximum ratings may damage the device. 2. the device is not guaranteed to function outside its operating ratings. 3. devices are esd sensitive. handling precautions are recommended. human body model, 1.5k ? in series with 100pf. 4. specification s a re for packaged product only.
micrel, inc. mic4604 june 25 , 2013 4 revision 1.0 electrical characteristics ( 4 ) (continued) v dd = v hb = 12v; v ss = v hs = 0v; no load on lo or ho; t a = +25c; unless otherwise noted. bold values indicate ? 40c t j +125c symbo l parameter condition min. typ. max. units lo gate driver v oll low - level output voltage i lo = 50ma 0.17 0.4 v v ohl high - level output voltage i lo = ? 50ma, v ohl = v dd ? v lo 0.25 1.0 v i ohl peak sink current v lo = 5 v 1 a i oll peak source curren t v lo = 5 v 1 a ho gate driver v olh low - level output voltage i ho = 50ma 0.2 0.6 v v ohh high - level output voltage i ho = ? 50ma, v ohh = v hb ? v ho 0.22 1.0 v i ohh peak sink current v ho = 5 v 1.5 a i olh peak source current v ho = 5 v 1 a switch ing specifications ( 5 ) t lphl lower turn - off propagation delay (li falling to lo falling) 37 75 ns t hphl upper turn - off propagation delay (hi falling to ho falling) 34 75 ns t lplh lower turn - on propa gation delay (li rising to lo rising) 39 75 ns t hplh upper turn - on propagation delay (hi rising to ho rising) 33 75 ns t rc/fc output rise/fall time c l = 1000pf 20 ns t r/f output rise/fall time (3v to 9v) c l = 0.1f 0.8 s t pw minimum inpu t pulse width that changes the output 50 ns t bs bootstrap diode turn - on or turn- off time 10 ns note: 5. guaranteed by design. not production tested.
micrel, inc. mic4604 june 25 , 2013 5 revision 1.0 timing diagrams note: 6. all propagation delays are measured from the 50% voltage level. b lock diagram figure 1 . mic4604 block diagram
micrel, inc. mic4604 june 25 , 2013 6 revision 1.0 typical characteristics 0 20 40 60 80 100 4 6 8 10 12 14 16 quiescent current (a) input voltage (v) quiescent current vs. input voltage hs = 0v t = 125 c t = - 40 c t = 25 c 0 50 100 150 200 250 300 4 6 8 10 12 14 16 v dd operating current (a) input voltage (v) v dd operating current vs. input voltage freq = 20khz hs = 0v vhb = vdd t = 125 c t = - 40 c t = 25 c 10 20 30 40 50 60 4 6 8 10 12 14 16 v hb operating current (a) input voltage (v) v hb operating current vs. input voltage freq = 20khz hs = 0v vhb = vdd t = - 40 c t = 125 c t = 25 c 0 20 40 60 80 100 -50 -25 0 25 50 75 100 125 quiescent current (a) temperature ( c) quiescent current vs. temperature hs = 0v vdd = 16v vdd = 12v vdd = 9v 50 100 150 200 250 300 -50 -25 0 25 50 75 100 125 v dd operating current (a) temperature ( c) v dd operating current vs. temperature freq = 20khz hs = 0v vhb = vdd vdd = 16v vdd = 12v vdd = 9v 15 20 25 30 35 40 45 -50 -25 0 25 50 75 100 125 v hb operating current (a) temperature ( c) v hb operating current vs. temperature freq = 20khz hs = 0v vhb = vdd vhb = 16v vhb = 12v vhb = 9v 0 2 4 6 8 0 200 400 600 800 1000 v dd operating (ma) frequency (khz) v dd operating current vs. frequency hs = 0v vhb = vdd =12v t = 125 c t = - 40 c t = 25 c 0 0.2 0.4 0.6 0.8 0 200 400 600 800 1000 v hb operating current (ma) frequency (khz) v hb operating current vs. frequency hs = 0v vhb = vdd = 12v t = - 40 c t = 125 c t = 25 c 0 100 200 300 400 500 -50 -25 0 25 50 75 100 125 v oll , v olh (mv) temperature ( c) low level output voltage vs. temperature hs = 0v i lo , i ho = 50ma vdd = 16v vdd = 12v vdd = 9v
micrel, inc. mic4604 june 25 , 2013 7 revision 1.0 typical characteristics (continued) 0 100 200 300 400 500 -50 -25 0 25 50 75 100 125 v ohl , v ohh (mv) temperature ( c) high level output voltage vs. temperature vdd = 16v vdd = 12v vdd = 9v hs = 0v i lo ,i ho = - 50ma 4.2 4.3 4.4 4.5 4.6 4.7 4.8 -50 -25 0 25 50 75 100 125 thresholds (v) temperature ( c) uvlo thresholds vs. temperature hs = 0v vhb rising vdd rising vdd falling vhb falling 0.16 0.18 0.20 0.22 0.24 0.26 0.28 -50 -25 0 25 50 75 100 125 hysteresis (v) temperature ( c) uvlo hysteresis vs. temperature hs = 0v vdd hysteresis vhb hysteresis 20 35 50 65 80 4 6 8 10 12 14 16 delay (ns) input voltage (v) propagation delay vs. input voltage t amb = 25 c hs = 0v t hplh t hphl t lplh t lphl 20 30 40 50 60 -50 -25 0 25 50 75 100 125 delay (ns) temperature ( c) propagation delay vs. temperature vdd = vhb = 12v hs = 0v t hplh t hphl t lplh t lphl 0.1 1 10 100 1000 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 forward current (ma) forward voltage (v) bootstrap diode i - v characteristics hs = 0v t = 125 c t = - 40 c t = 25 c 0.0001 0.001 0.01 0.1 1 10 100 0 10 20 30 40 50 60 70 80 90 100 reverse current (a) reverse voltage (v) bootstrap diode reverse current t = 125 c t = 25 c t = 85 c hs = 0v
micrel, inc. mic4604 june 25 , 2013 8 revision 1.0 functional description the mic4604 is a high - voltage, non - inverting, dual mosfet driver that is designed to independently drive both high - side and low - side n - channel mosfets. the block diagram of the mic4604 is shown in figure 1 . both drivers contain an input buffer with hysteresis, a uvlo circuit , and an output buffer. the high - side output buffer includes a high - speed level - shifting circuit that is referenced to the hs pin. an internal diode is used as part of a bootstrap circuit to provide the drive voltage for the high - side output. startup and uvlo the uvlo circuit forces the driver output low until the supply voltage exceeds the uvlo threshold. the low - side uvlo circuit monitors the voltage between the vdd and vss pins. the high - side uvlo circuit monitors the volt age between the hb and hs pins. hysteresis in the uvlo circuit prevents noise and finite circuit impedance from causing chatter during turn - on. input stage both the hi and li pins of the mic4604 are referenced to the vss pin. the voltage state of the input signal does not change the quiescent current draw of the driver. the mic4604 has a ttl - compat ible input range and can b e used with input signals with amplitude less than the supply voltage. the threshold level is independent of the vdd supply voltage and there is no dependence between i vdd and the input s ignal amplitude with the mic4604 . this feature makes t he mic4604 an excellent level tr anslator that will drive high - threshold mosfets from a low - voltage pwm ic. low - side driver a block diagram of the low - s ide driver is shown in figure 2 . the low - side driver is designed to drive a gr ound (vss pin) referenced n - channel mosfet. low driver impedances allow the external mosfet to be turned on and off quickly. the rail - to - rail drive capability o f the output ensures a low r d s on from the external mosfet. a high level applied to li pin causes the upper driver mos fet to turn on and vdd voltage is applied to the gate of the external mosfet. a low level on the li pin turns off t he upper driver and turns on the low side driver to ground the gate of the external mosfet. figure 2 . low - side driver block diagram high - side driver and bootstrap circuit a block diagram of the high - side driver and bootst rap c ircuit is shown in figure 3 . this driver is designed to drive a floating n - channel mosfet, whose source terminal is referenced to the hs pin. figure 3 . high - side driver and bootstrap ci rcuit block diagram a low - power, high - speed, level - shifting circuit isolates the low side (vss pin) referenced circuitry from the high - side (hs pin) referenced driver. power to the high - side driver and uvlo circuit is supplied by the bootstrap circuit whi le the voltage level of the hs pin is shifted high.
micrel, inc. mic4604 june 25 , 2013 9 revision 1.0 the bootstrap circuit consists of an internal diode and external capacitor, c b . in a typical application, such as the synchronous buck converter shown in figure 4 , the hs pin is at ground potential while the low - side mosfet is on. the internal diode allows capacitor c b to charge up to v dd- v f during this time (where v f is the forward voltage drop of the internal diode). after the low - side mosfet is turned off and th e ho pin turns on, the voltage across capacitor c b is applied to the gate of the upper external mosfet. as the upper mosfet turns on, voltage on the hs pin rises with the source of the high - side mosfet until it reaches vin . as the hs and hb pin rise, the i nternal diode is reverse biased preventing capacitor c b from discharging. figure 4 . high - side driver and bootstrap circuit block diagram programmable gate drive the mic4604 offers programma ble gate drive, which means the mosfet g ate drive ( g ate to s ource v oltag e) equals the vdd voltage. this feature offers de signers flexibility in driving the mosfets . different mosfets require different vgs characteristics for optimum r dson performance. typically, the higher the g ate voltage (up to 16v) , the lower the r dson achieved. for example, a 48 99 mosfet can be driven to the on stat e at 4.5v g ate voltage but r dson is 7.5m. if driven to 10v g ate voltage, r dson is 4.5m . in low - current application s , the losses due to r dson are minimal, but i n high - current applications such as power hand tools, the difference in r dson can cut into the efficiency budget. in portab le hand tools and other battery - powered applications, the mic4604 offers the ability to drive motors at a lower voltage compared to the traditional mosfet drivers because of the wide vdd range (5.5v to 16v). traditional mosfet drivers typically r equire a vdd greater than 9v. the mic4604 drives a mot or using only two li - i on batteries (total 7.2v) compared to traditional mosfet drive rs w hich will require at least three c ells (total of 10.8v) t o exceed the minimal vdd range. as an additional benefit, the low 5.5v gate drive capability allow s a longer run time. this is because the li - i on battery can run down to 5.5v , which is just above its 4.8v minimum recommended discharge voltage . this is also a benefit in higher current power tools that use five or six cells. the driver can be ope rated up to 16v to minimize the r dson of the mosfets and use as much of the discharge battery pack as p ossibl e for a longer run time. for example, an 18v battery pack can be used to the lowest operati ng discharge voltage of 13.5v. application information power dissipation considerations power dissipation in the driver can be separated into three areas: ? internal diode dissipation in the bootstrap circuit ? internal driver dissipation ? quiescent current dissipation used to supply the internal logic and control functions . bootstrap circuit power dissipation power dissipation of the internal bootstrap diode primarily co mes from the average charging current of the c b capacitor multiplied by the forward voltage drop of the diode. secondary sources of diode power dissipation are the reverse leakage current and reverse recovery effects of the diode. the average current drawn by repeated charging of the high - side mosfet is calculated by: s gate ) ave ( f f q i = eq. 1 where: q gate = total gate charge at v hb f s = gate drive switching frequency the average power dissipated by the forward voltage drop of the diode equals: f ) ave ( f fwd v i pdiode = eq. 2 where: v f = diode forward voltage drop the value of v f should be taken at the peak current through the diode ; however, this current is difficult to calculate because of differences in source impedances. the peak current can either be measured or the value of v f at the average current can be used, which will yield a good approximation of diode power dissipation. the reverse leakage current of the internal bootstrap diode is typically 2 a at a reverse voltage of 85 v at 125c. power
micrel, inc. mic4604 june 25 , 2013 10 revision 1.0 dissi pation due to reverse leakage is typically much less than 1mw and can be ignored. reverse recovery time is the time required for the injected minority carriers to be swept away from the depletion region during turn - off of the diode. power dissipation due t o reverse recovery can be calculated by computing the average reverse current due to reverse recovery charge times the reverse voltage across the diode. the average reverse current and power dissipation due to reverse recovery can be estimated by: rev ) ave ( rr rr s rr rrm ) ave ( rr v i pdiode f t i 5 . 0 i = = eq. 3 where: i rrm = peak reverse recovery curren t t rr = reverse recovery time the total diode power dissipation is: rr fwd total pdiode pdiode pdiode + = eq. 4 an optional external bootstrap diode may be used instead of the internal diode ( figure 5 ). an external diode may be useful if high gate charge mosfets are being driven and the power dissipation of the internal diode is contributing to excessive die temperatures. the voltage drop of the external diode must b e less than the internal diode for this option to work. the reverse voltage across the diode will be equal to the input voltage m inus the vdd supply voltage. the above equations can be used to calculate power dissipation in the external diode ; however, if the external diode has significant reverse leakage current, the power dissipated in that diode due to reverse leakage can be calculated as: ) d 1 ( v i pdiode rev r rev ? = eq. 5 where: i r = reverse current flow at v rev and t j v rev = diode reverse voltage d = duty cycle = t on f s the on - time is the time the high - side switch is conducting. in most topologies, the diode is reverse biased during the switching cycle off - time. figure 5 . optional bootstrap diode gate driver power dissipation power dissipation in the output driver stage is mainly caused by charging and discharging the gate to source and gate to drain capacitance of the external mosfet. figure 6 shows a simplified equivalent circuit of t he mic4604 driving an external mosfet. figure 6 . mic4604 driving an external mosfet dissipation d uring the e xternal mosfet turn - on energy from capacitor c b is used to charge up the input capacitance of the mosfet (cgd and cgs). the energy delivered to the mosfet is dissipated in the three resistive components, ron, rg and rg_fet. ron is the on resistance of the upper driver mosfet in the mic4604 .
micrel, inc. mic4604 june 25 , 2013 11 revision 1.0 rg is the series resistor (if any) between the driver ic and the mosfet. rg_fet is the gate resistance of the mosfet. rg_fet is usually listed in the power mosfet?s specifications. the esr of capacitor c b and the resistance of the connecting etch can be ignored since they are much less than ron and rg_fet. the effective capacitance s of c gd and cgs are difficult to calculate because they vary non - linearly with id, vgs, and vds. fortunately, most power mosfet specifications include a typical graph of tot al gate charge versus vgs. figure 7 shows a t ypical gate charge curve for an arbitrary power mosfet. this chart shows that for a gate voltage of 10v, the mosfet requires about 23.5nc of charge. the energy dissipated by the resistive components of the gate drive circuit during turn - on is calculated as : gs 2 gs 2 1 v qg 1/2 e so v c q but v ciss e = = = eq. 6 where ciss = total gate capacitance of the mosfet 10 8 6 4 2 0 0 5 10 15 20 25 gate charge q g - t otal gate charge (nc ) v gs - gate-to-source v oltage (v ) v ds = 50v i d = 6.9a figure 7 . typical gate charge vs. vgs the same energy is dissipated by roff, rg and rg_fet when the driver ic turns the mosfet off. assuming ron is approximately equal to roff, the total energy and power dissipated by the resistive drive elements is: fs v qg p and v qg e gs driver gs driver = = eq. 7 where: e driver = energy dissipated per switching cycle p driver = power dissipated per switching cycle qg = total gate c harge at vgs vgs = gate to s ource voltage on the mosfet fs = switching frequency of the gate drive circuit the power dissipated inside the mic4604 is equal to the ratio of ron and roff to the external resistive losses in rg and rg_fet. letting ron = roff, the power dissipated in the mic4604 due to driving the external mosfet is: fet _ rg rg ron ron p pdiss driver drive + + = eq. 8 supply current power dissipation power is dissipated in the mic4604 even if nothing is being driven. the supply current is drawn by the bias for the in ternal circuitry, the level shifting circuitry , and shoot - through current in the output drivers. the supply current is proportional to operating frequency and the vdd and vhb voltages. the typical characteristic graphs show how supply current varies with s witching frequency and supply voltage. the power dissipated by the mic4604 due to supply current is ihb vhb idd vdd pdiss ply sup + = eq. 9 total p ower d issipation and thermal considerations total power dissipation in the mic4604 is equal to the power dissipation ca used by driving the external mosfets, the supply current and the internal bootstrap diode. total drive ply sup total pdiode pdiss pdiss pdiss + + = eq. 10
micrel, inc. mic4604 june 25 , 2013 12 revision 1.0 the die temperature can be calculated after the total power dissipation is known. ja total a j pdiss t t + = eq. 11 where: t a = maximum ambient temperature t j = junction temperature ( c) pdiss total = power dissipation of the mic4604 ja = thermal resistance from junction to ambient air propagation d elay and o ther timing considerations propag ation delay and signal timing are important consi deration s . many power supply topologies use two switching mosfets operating 180 out of phase from each other. these mosfets must not be on at the same time or a short circuit will occur, causing high peak currents and higher power dissipation in the mosfe ts. the mic4604 output gate drivers are not designed with anti - shoot - through protect ion circuitry. the output drive signals simply follow the inputs. the power supply design must include timing delays (dead - time) between the input signals to prevent shoot - through. make sure the input signal pulse width is greater than the minimum specified pulse width. an input signal that is less than the minimum pulse width may result in no output pulse or an output pulse whose width is significantly less than the input. the maximum duty cycle (ratio of high side on - time to switching period) is controlled by the minimum pulse width of the low side and by the time required for the c b capacitor to charge during the off - time. adequate time must be allowed for the c b capacit or to charge up before the high - side driver is turned on. decoupling and bootstrap capacitor selection decoupling capacitors are required for both the low side (vdd ) and high side (hb) supply pins. these capacitors supply the charge necessary to drive the external mosfets and also minimize the voltage ripple on these pins. the capacitor from hb to hs has two functions: it provides decoupling for the high - side circuitry and also provid es current to the high - side circuit while the high - side external mosfet is on. ceramic capacitors are recommended because of their low impedance and small size. z5u type ceramic capacitor dielectrics are not recommende d because of the large change in capacitance over temperature and v oltage. a minimum value of 0.1 f is required for each of the capacitors, regardless of the mosfets being driven. larger mosfets may require larger capacitance values for proper operation. the voltage rating of the capacitors depends on the supply voltage, ambient temperature and the voltage derating used for reliability. 25v rated x5r or x7r ceramic capacitors are recommended for most applications. the minimum capacitance value should be increased if low voltage capacitors are use d because even good quality dielectric capacitors, such as x5r, will los e 40% to 70% of their capacitance value at the rated voltage. placement of the decoupling capacitors is critic al. the bypass capacitor for vdd should be placed as c lose as possible between the vdd and vss pins. the bypass capacitor (c b ) for the hb supply p in must be located as close as possible between the hb and hs pins. the etch connections must be short, wide , and direct. the use of a ground plane to minimize connection impedance is recommended. refer to the section on grounding, component placement and circuit layout for more information. the voltage on the bootstrap capacitor drops each time it delivers charge to turn on the mosfet. the voltage drop depends on the gate charge required by the mosfet. most mosfet specifications specify gate charge versus vgs voltage. based on this information and a recommended v hb of less than 0.1v, the minimum value of bootstrap capacitance is calculated as: hb gate b v q c ? eq. 12 where: q gate = total gate charge at v hb ? v hb = voltage drop at the hb pin the decou pling capacitor for the vdd input may be calculated in wi th the same formula; however, the two capacitors are usually equal in value. grounding, component placement and circuit layout nanosecond switching speeds and ampere peak currents in and around the mic4604 drivers require proper placement and trace routing of all components. improper placement may cause degraded noise immunity, false switching, excessive ringing , or circuit latch - up. figure 8 shows the critical current paths when the driver outputs go high and turn on the external mosfets. it also helps demonstrate the need for a low impedance ground plane. charge needed to turn - on the mosfet gates comes from the decoupling capacitors c vdd and c b . current in the low - side gate driver flows from c vdd through the intern al driver, into the mosfet gate , and out the s ource. the return connection back to the decoupling capacitor is made through the ground plane. any inductance or resistance in the ground return path causes a voltage spike or ringing to appear on the source o f the mosfet. this voltage works against the gate drive voltage and can either slow down or turn off the mosfet during the period when it should be turned on.
micrel, inc. mic4604 june 25 , 2013 13 revision 1.0 current in the high - side driver is sourced from capacitor c b and flows into the hb pin and out th e ho pin, into the gate of the high side mosfet. the return path for the current is from the source of the mosfet and back to capacitor c b . the high - side circuit return p ath usually does not have a low - impedance ground plane so the etch connections in this critical path should be short and wide to minimize parasitic inductance. as with the low - side circuit, impedance between the mosfet source and the decoupling capacitor causes negative voltage feedback that fights the turn - on of the mosfet. it is important to note that capacitor c b must be placed close to the hb and hs pins. this capacitor not only provides all the energy for turn - on but it must also keep hb pin noise and ripple low for proper operation of the high - side drive circuitry. figure 8 . turn - on current paths figure 9 shows the critical current paths when the driver outputs go low and turn off the external mosfets. short, low - impedance connections are important during turn - off fo r the same reasons given in the turn - on explanation. current flowing through the internal diode replenishes charge in the bootstrap capacitor, c b . figure 9 . turn - off current paths dc motor applications mic4604 mosfet d rivers ar e widely used in dc motor applications. they address brushed motors in both h alf - b ridge and f ull - b ridge motor topologies as wel l as 3 - phase brushless motors. as shown in figure 10 , figure 11 , and figure 12 , the drivers switch the mosfets at variable duty cycles that mod ulate the voltage to control motor speed. in the h alf - b ridge topology, the mo tor turn s in one direction only. the f u ll - b ridge topology allows for bidirectional control . 3 - phase motors are more efficient compa red to the brushed motors but require three half - bridge switches and additional circuitry to sense the position of the rotor. the mic4604 85v operating voltage off ers the engineer margin to protect against back electromotive force (emf) which is a voltage spike caused by the rotation of the roto r. the back emf voltage amplitude depends on the speed of the rotation. it i s good practice to have at least twice the hv v oltage of the motor supply. 85v is plenty of margin for 12v , 24v, and 40v motors.
micrel, inc. mic4604 june 25 , 2013 14 revision 1.0 figure 10 . half bridge dc motor figure 11 . full bridge dc motor figure 12 . 3 - phase br ushless dc motor driver ? 24v block diagram the mic4604 is offered in a small 2.5mm 2.5mm t dfn package for applic ations that are space constrained and an soic - 8 package for ease of manufacturing. the motor trend is to put the motor control circuit insid e the motor casing, which requires small packaging because of the size of the motor. the mic4604 offers low uvlo threshold and programmable gate drive , which allows for longer operation time in battery operated mo tors such as power hand tools. cross cond uction across the half bridge can cause catastrophic failure in a motor applica tion. engineers typically add dead time between states that switch betwee n h igh i nput and l ow i nput to en sure that the l ow - side mosfet completely turns off before the high - s ide mosfet turns on and vice versa. the dead time depends on the mosfet used in the application , but 200ns is typical for most motor applications. power inverter power i nverters are used to supply ac loads from a dc operated battery system, mainly during pow er failure. the battery voltage can be 12vdc, 24vdc , or up to 36vdc , depending on the power requirements. there two popular conversion methods, type i and type ii , that convert the battery energy to ac line v oltage (110vac or 230vac).
micrel, inc. mic4604 june 25 , 2013 15 revision 1.0 figure 13 . type i i nverter t opology as shown in figure 13 , type i is a dual - stage topology where line voltage is converted to dc through a transformer to charge the storage batteries. when a power failure is detected, the stored dc energy is converted to ac through another transformer to drive the ac loads con nected to the inverter output. this method is simplest to design but tends to be bulky and expensive because it uses two transformers. type ii is a single - stage topology that uses only one transformer to charge the bank of batteries to store the energy. during a power outage, the same transformer is used to power the line voltage. the t ype ii switch es at a higher frequency compared to the type i topo logy to maintain a small transformer size. both types require a half bridge or full bridge to pology to boost the dc to ac. t his application can use t wo mic4604s . the 85v operating voltage offers enough margin to address all of the available bank s of batte ries commonly used in inverter application s . the 85v operating voltage allows designers to increase the bank of batteries up to 72v , if desired. the mic4604 can sink as much as 1a , which is enough current to overcome the mosfet?s input capacitance and swit ch the mosfet up to 50khz. this makes the mic4604 an ideal solution for inverter applications. as with all half bridge and full bridge topologies, cross conduction is a concern to inverter manufactures because it can cause catastrophic failure . this can be remedied by adding the appropriate dead time between transitioning from the high - side mosfet to the low - s ide mosfet and vice versa. layout guidelines use the following layout guidelines for optimum circuit performance: ? place t he vdd and hb bypass capa citors close to the supply and ground pins. it is critical that the etch length between the high side decoupling capacitor (c b ) and the hb and hs pins be minimized to reduce lead inductance. ? use a ground plane to minimize parasitic inductance and impedanc e of the return paths. the mic4604 is capable of greater than 1a peak currents and any impedance between the mic4604, the decoupling capacitors , and the external mosfet will degrade the performance of the driver. ? trace out the high di/dt and dv /dt paths, a s shown in figure 14 and figure 15 , and minimize etch length and loop area for these connections. minimizing these parameters decreases the parasitic inductance and the rad iated emi generated by fast rise and fall times. a typical layout of a synchronous buck converter power stage ( figure 14 ) is shown in figure 15 . figure 14 . synchronous buck converter power stage the high - side mosfet drain connects to the input supply voltage (drain) and the source connects to the switching node. the low - side mosfet drain connects to the switching node and its source is connected to ground. the buck converter output inductor (not shown) connect s to the switching node. the high - side drive trace, ho, is routed on top of its return trace, hs, to minimize loop area and parasitic inductance. the low - side drive trace lo is routed over t he ground plane to minimize the impedance of that current path. the decoupling capacitors, c b and c vdd , are placed to minimize etch length between the capacitors and their respective pins. this close placement is necessary to efficiently charge capacitor c b when the hs node is low. all traces are 0.025 in wide or greater to reduce impedance. c in is used to decouple the high cu rrent path through the mosfets.
micrel, inc. mic4604 june 25 , 2013 16 revision 1.0 top side bottom side figure 15 . typical layout of a synchronous buck converter power stage
micrel, inc. mic4604 june 25 , 2013 17 revision 1.0 p ackage information and recommended land pattern ( 7 ) 8 - pin soic (m) note: 7. package information is correct as of the publication date. for updates and most current information, go to www.micrel.com .
micrel, inc. mic4604 june 25 , 2013 18 revision 1.0 package information and recommended land pattern (continued) ( 7 ) 2.5mm 2.5mm 10- pin t dfn (mt ) micrel, inc. 2180 fortun e drive san jose, ca 95131 usa tel +1 (408) 944 - 0800 fax +1 (408) 474 - 1000 web http://www.micrel.com micrel makes no representations or warranties with respect to the accuracy or completeness of the informati on furnished in this data sheet. this information is not intended as a warranty and micrel does not assume responsibility for its use. micrel reserves the right to change circuitry, specifications and descriptions at any time without notice. no license, whether express, implied, arising by estoppel or otherwise, to any intellectual property rights is granted by this document. except as provided in micrel?s terms and conditions of sale for such products, micrel assumes no liability whatsoever, and micrel disclaims any express or implied warranty relating to the sale and/or use of micrel products including liability or warrantie s relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual pro perty right . micrel products are not designed or authorized for use as components in life support appliances, devices or systems where mal function of a product can reasonably be expected to result in personal injury. life support devices or systems are de vices 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 signific ant injury to the user. a purchaser?s use or sale of micrel products fo r 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. ? 20 13 micrel, incorporated.

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