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fn7889 rev 0.00 page 1 of 21 september 30, 2015 fn7889 rev 0.00 september 30, 2015 isl8018 8a low quiescent current high efficiency synchronous buck regul ator datasheet the isl8018 is a high efficiency, monolithic, synchronous step-down dc/dc converter that can deliver up to 8a continuous output current from a 2.7v to 5.5v input supply. the output voltage is adju stable from 0.6v to v in . with an adjustable current limit, reverse current protection, prebias start and over-temperature protection, the isl8018 offers a highly robust power solution. it uses current control architecture to deliver fast tr ansient response and excellent loop stability. the isl8018 integrates a pair of low on-resistance p-channel and n-channel internal mosfets to maximize efficiency and minimize external componen t count. 100% duty-cycle operation allows less than 250mv dropout at 8a output current. adjustable frequency and synchronization allow the isl8018 to be used in applications requiring low noise. the isl8018 can be configured for discontinuous or forced continuous operation at light load. forced continuous operation reduces noise and rf interferen ce while discontinuous mode provides high efficiency by redu cing switching losses at light loads. the isl8018 is offered in a space saving 20 ld 3x4 qfn lead free package with exposed pad lead frames for excellent thermal performance. the complete converter occupies less than 96.8mm 2 area. see ordering information on page 2 for more detail. related literature ? ug052 ?isl8018demo1z demonstr ation board user guide? ? ug053 ?ISL8018EVAL3Z evaluation board user guide? features ? high efficiency synchronous buck regulator with up to 97% efficiency ? 10% output voltage margining ? adjustable current limit ? start-up with prebiased output ? internal soft-start - 1ms or adjustable, internal/external compensation ? soft-stop output discharge during disabled ? adjustable frequency from 500khz to 4mhz - default at 1mhz ? external synchronization up to 4mhz - master to slave phase shifting capability ? peak current limiting, hiccup mo de short-circuit protection and over-temperature protection applications ? dc/dc pol modules ? c/p, fpga and dsp power ? plug-in dc/dc modules for routers and switchers ?portable instruments ? test and measurement systems ? li-ion battery powered devices figure 1. efficiency t = +25c v in = 5v 70 75 80 85 90 95 100 012345678 efficiency (%) i out (a) 3.3v out pwm 3.3v out pfm
isl8018 fn7889 rev 0.00 page 2 of 21 september 30, 2015 pin configuration isl8018 (20 ld qfn) top view ordering information part number ( notes 1 , 2 , 3 )part marking output voltage (v) temp. range (c) package (rohs compliant) pkg. dwg. # isl8018irajz 018a adjustable -40 to +85 20 ld 3x4 qfn l20.3x4 ISL8018EVAL3Z evaluation board isl8018demo1z demonstration board notes: 1. add ?-t? suffix for 6k units or ?-t7a? suffix for 250 units tape and reel options . please refer to tb347 for details on reel specifications. 2. these intersil pb-free plastic packaged products employ spec ial pb-free material sets, molding compounds/die attach materials , and 100% matte tin plate plus anneal (e3 termination finish , which is rohs compliant and compatible wi th both snpb and pb-free soldering opera tions). intersil pb-free products are msl classified at pb-fr ee peak reflow temperatures that meet or exceed the pb-free requirements of ipc/jed ec j std-020. 3. for moisture sensitivity level (msl), please see device information page for isl8018 . for more information on msl please see techbrief tb363 . 1 3 4 pgnd phase phase pgnd sgnd vfb syncin 2 6 9 7 8 vset fs en comp vin vin pg phase 5 10 15 13 12 14 11 20 17 19 18 16 syncout iset ss pgnd vin pad
isl8018 fn7889 rev 0.00 page 3 of 21 september 30, 2015 pin descriptions pin symbol description 1, 19, 20 pgnd power ground. 2, 3, 4 phase switching node connection. connect to one terminal of the inductor. 5, 6, 7 vin input supply voltage. connect two 22f ceramic capacitors to power ground. 8 pg power-good is an open-drain output. use 10k to 100k pull-up resistor connected between vin and pg. at power-up or en hi, pg rising edge is de layed by 1ms from the output reaching regulation. 9 syncout this pin outputs a 250a current source that is tu rned on at the rising edge of the internal clock or syncin. when syncout voltage reaches 0.8v, a reset circuit will activate and discharge syncout to 0v. syncout is held at 0v in pfm li ght load to reduce quiescent current. 10 syncin mode selection pin. connect to logic high or input voltage vin for pwm mode. connect to logic low or ground for pfm mode. connect to an external functi on generator for synchroniz ation with the positive edge trigger. there is an internal 1m pull-down resistor to prevent an undefined logic state if syncin is floating. 11 en regulator enable pin. enables the output when driven to high. shuts down the chip and discharges the output capacitor when driven to low. 12 fs this pin sets the oscillator swit ching frequency, using a resistor, r fs , from the fs pin to gnd. the frequency of operation may be programmed between 500khz to 4mhz. the default frequency is 1mhz and configured for internal compensa tion if fs is connected to vin. 13 vset vset is the output margining se tting of the regulators. connect to sgnd for -10%, keep it floating for no margining and connect to vin for +10%. 14 iset iset is the peak output current limit and skip cu rrent limit setting of the regulators. connect to sgnd for 3a, to vin for 5a and keep it floating for 8a. 15 ss ss is used to adjust the soft-start time. set to sgnd for internal 1ms rise time. connect a capacitor from ss to sgnd to adjust the soft-start time. do not use more than 33nf per ic. 16, 17 comp, vfb the feedback network of the regulator, vfb, is the negative input to the transconductance error amplifier. comp is the output of the amplifier if the fs resistor is used. if internal compensation is used (fs = vin), the comp pin should be tied to sgnd. the ou tput voltage is set by an external resistor divider connected to vfb. with a properly selected divider, the output voltage can be set to any voltage between vin and the 0.6v reference. while internal compensation offers a solution for many typical applications, an external compensation network may offer improved performance for some designs. in addition to regulation, vfb is also used to determine the state of pg. 18 sgnd signal ground. epad the exposed pad must be connected to the sgnd pi n for proper electrical performance. place as many vias as possible under the pad connecting to th e system gnd plane for optimal thermal performance.
isl8018 fn7889 rev 0.00 page 4 of 21 september 30, 2015 typical application diagrams l 1h phase pgnd vfb vin en pg syncout input 2.7v to 5.5v output 1.8v/8a c 1 isl8018 c 2 r 2 200k r 3 100k 2x47f ss sgnd c 3 * 15pf r 1 100k figure 2. typical application diagram - single chip 8a comp syncin fs iset vset vin * c 3 is optional. recommend putting a placeholder for it. check loop analysis first before use. 2x22f
isl8018 fn7889 rev 0.00 page 5 of 21 september 30, 2015 block diagram figure 3. functional block diagram phase + + csa + + ocp skip + + + slope comp slope soft start soft- eamp comp pwm/pfm logic controller protection hs driver vfb + 0.85*vref pg syncin shutdown vin pgnd oscillator zero-cross sensing bandgap scp + 0.1v en shutdown 1ms delay 55pf 168k sgnd 3pf 6k - - - - - - - vdd ss comp 100 shutdown ls driver syncout fs iset threshold iset vset vref + neg current sensing 250a p n + 0.8v - uv ov
isl8018 fn7889 rev 0.00 page 6 of 21 september 30, 2015 absolute maximum ratings (reference to gnd) thermal information vin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3v to 5.8v (dc) or 7v (20ms) en, fs, iset, pg, syncout, syncin vfb, vset . . . . . . -0.3v to vin + 0.3v phase . . . . . . . . . . . . -1.5v (100ns)/-0.3v (dc) to 6.5v (dc) or 7v (20ms) comp, ss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3v to 2.7v esd rating human body model (tested per jesd22-a114) . . . . . . . . . . . . . . . . . 3kv machine model (tested per jesd22-a115). . . . . . . . . . . . . . . . . . . . 300v charged device model (tested per jesd22-c101e). . . . . . . . . . . . . .1.5v latch-up (tested per jesd-78a; class 2, level a) . . . . . .100ma at +85c thermal resistance (typical) ? ja (c/w) ? jc (c/w) 3x4 qfn package ( notes 4 , 5 ) . . . . . . . . . . 42 5 junction temperature range . . . . . . . . . . . . . . . . . . . . . . .-55c to +125c storage temperature range. . . . . . . . . . . . . . . . . . . . . . . .-65c to +150c pb-free reflow profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . see tb493 recommended operating conditions vin supply voltage range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7v to 5.5v load current range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0a to 8a ambient temperature range . . . . . . . . . . . . . . . . . . . . . . . . -40c to +85c caution: do not operate at or near the maximum ratings listed for extended periods of time. exposure to such conditions may adv ersely impact product reliability and result in failures not covered by warranty. notes: 4. ? ja is measured in free air with the componen t mounted on a high effective thermal conduc tivity test board with ?direct attach? fe atures. see tech brief tb379 . 5. ? jc , ?case temperature? location is at the center of the exposed metal pad on the package underside. analog specifications all parameter limits are established across the recomme nded operating conditions and are measured at the following conditions: t a = -40c to +85c, v in = 3.6v, en = v in , unless otherwise noted. typical values are at t a = +25c. boldface limits apply across the operating temperature range, -40c to +85c. parameter symbol test conditions min ( note 6 )typ max ( note 6 )unit input supply v in undervoltage lockout threshold v uvlo rising, no load 2.5 2.7 v falling, no load 2.2 2.4 v quiescent supply current i vin syncin = gnd, no load at the output 70 a syncin = gnd, no load at the output and no switches switching 70 95 a syncin = vin, f sw = 1mhz, no load at the output 8 15 ma shutdown supply current i sd syncin = gnd, v in = 5.5v, en = low 5 9.5 a output regulation reference voltage v ref v set = v in 0.651 0.660 0.669 v v set = float 0.594 0.600 0.606 v v set = sgnd 0.531 0.540 0.549 v output voltage margining v vfb v set = v in , percent of output changed 9.5 10 10.5 % v set = sgnd, percent of output changed -10.5 -10 -9.5 % vfb bias current i vfb vfb = 0.75v 0.1 a fixed output vfb bias current i vfb v set = float, vfb = 10% above output 6 a line regulation v in = v o + 0.5v to 5.5v (minimal 2.7v) 0.2 %/v soft-start ramp time cycle ss = sgnd 1 ms soft-start charging current iss v ss = 0.1v 1.4 1.8 2.2 a overcurrent protection current limit blanking time t ocon 17 clock pulses overcurrent and auto restart period t ocoff 8 ss cycle
isl8018 fn7889 rev 0.00 page 7 of 21 september 30, 2015 positive peak current limit iplimit i set = float 9.7 12.8 15.8 a i set = v in 6.7 8.8 10.9 a i set = sgnd 4 5.6 7.2 a peak skip limit i skip i set = float 2.18 2.8 3.78 a i set = v in 1.08 1.66 2.3 a i set = sgnd 1.05 a zero cross threshold -300 300 ma negative current limit inlimit -4.25 -3 -1.75 a compensation error amplifier transconductance fs = v in 100 a/v fs with resistor 200 a/v transresistance rt 0.11 phase p-channel mosfet on-resistance v in = 5v, i o = 200ma 31 45 m v in = 2.7v, i o = 200ma 44 55 m n-channel mosfet on-resistance v in = 5v, i o = 200ma 19 35 m v in = 2.7v, i o = 200ma 25 50 m phase maximum duty cycle 100 % phase minimum on-time syncin = high 140 ns oscillator nominal switching frequency f sw fs = v in 800 1000 1200 khz fs with rs = 402k 440 520 600 khz fs with rs = 42.4k 3200 3700 4200 khz syncin logic low to high transition range 0.70 0.75 0.80 v syncin hysteresis 0.15 v syncin logic input leakage current v in = 3.6v 3.6 5 a syncout charging current iso pwm 210 250 290 a pfm 0 a syncout voltage low 0.3 v pg output low voltage 0.3 v delay time (rising edge) 0.5 1 2 ms pg pin leakage current 0.01 0.1 a ovp pg rising threshold 0.80 v uvp pg rising threshold 80 85 90 % uvp pg hysteresis 5% pgood delay time (falling edge) 7s analog specifications all parameter limits are established across the recomme nded operating conditions and are measured at the following conditions: t a = -40c to +85c, v in = 3.6v, en = v in , unless otherwise noted. typical values are at t a = +25c. boldface limits apply across the operating temperature range, -40c to +85c. (continued) parameter symbol test conditions min ( note 6 )typ max ( note 6 )unit
isl8018 fn7889 rev 0.00 page 8 of 21 september 30, 2015 iset, vset logic input low 0.4 v logic input float 0.5 0.8 v logic input high 0.9 v logic input leakage current 0.1 1 a en logic input low 0.4 v logic input high 0.9 v en logic input leakage current 0.1 1 a thermal shutdown 150 c thermal shutdown hysteresis 25 c note: 6. compliance to datasheet limits is assu red by one or more methods: production test, characterization and/or design. analog specifications all parameter limits are established across the recomme nded operating conditions and are measured at the following conditions: t a = -40c to +85c, v in = 3.6v, en = v in , unless otherwise noted. typical values are at t a = +25c. boldface limits apply across the operating temperature range, -40c to +85c. (continued) parameter symbol test conditions min ( note 6 )typ max ( note 6 )unit
isl8018 fn7889 rev 0.00 page 9 of 21 september 30, 2015 typical operating performance unless otherwise noted, operating conditions are: t a = +25c, v in = 5v, en = 3.3v, syncin = v in , l = 1h, c 1 = 2x22f, c 2 = 4x22f, v out = 1.8v, i out = 0a to 8a. figure 4. efficiency vs load (1mhz 3.3v in pwm) figure 5. efficien cy vs load (1mhz 3.3v in pfm) figure 6. efficiency vs load ( 1mhz 5v in pwm) figure 7. efficiency vs load ( 1mhz 5v in pfm ) figure 8. power dissipation vs load (1mhz, v out = 1.8v) figure 9. v out regulation vs v in (pwm v out = 1.8v) 40 50 60 70 80 90 100 012345678 efficiency (%) i out (a) 1.2v out 1.5v out 1.8v out 2.5v out 40 50 60 70 80 90 100 012345678 i out (a) efficiency (%) 1.2v out 1.5v out 1.8v out 2.5v out 40 50 60 70 80 90 100 012345678 efficiency (%) i out (a) 1.2v out 1.5v out 1.8v out 2.5v out 3.3v out 40 50 60 70 80 90 100 01 2345678 efficiency (%) i out (a) 1.2v out 1.5v out 1.8v out 2.5v out 3.3v out 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 012345678 pd (w) i out (a) 3.3v in pwm mode 5v in pwm mode 1.775 1.780 1.785 1.790 1.795 1.800 1.805 1.810 1.815 2.5 2.8 3.1 3.4 3.7 4.0 4.3 4.6 4.9 5.2 5.5 v out (v) i out (a) 0a load 4a load 8a load
isl8018 fn7889 rev 0.00 page 10 of 21 september 30, 2015 figure 10. v out regulation vs v in (pfm v out = 1.8v) figure 11. v out regulation vs load (1mhz, v out =1.2v) figure 12. v out regulation vs load (1mhz, v out = 1.5v) figure 13. v out regulation vs load (1mhz, v out =1.8v) figure 14. v out regulation vs load (1mhz, v out =2.5v) figure 15. v out regulation vs load (1mhz, v out =3.3v) typical operating performance unless otherwise noted, operating conditions are: t a = +25c, v in = 5v, en = 3.3v, syncin = v in , l = 1h, c 1 = 2x22f, c 2 = 4x22f, v out = 1.8v, i out = 0a to 8a. (continued) 1.775 1.783 1.791 1.799 1.807 1.815 1.823 1.831 1.839 1.847 2.5 2.8 3.1 3.4 3.7 4.0 4.3 4.6 4.9 5.2 5.5 v out (v) i out (a) 0a load 8a load 4a load 1.182 1.188 1.194 1.200 1.206 1.212 1.218 1.224 1.230 0 12345678 v out (v) i out (a) 5v in pwm mode 5v in pfm mode 3.3v in pwm mode 3.3v in pfm mode 1.479 1.485 1.491 1.497 1.503 1.509 1.515 1.521 1.527 012345678 v out (v) i out (a) 5v in pwm mode 5v in pfm mode 3.3v in pwm mode 3.3v in pfm mode 1.773 1.780 1.787 1.794 1.801 1.808 1.815 1.822 1.829 012345678 v out (v) i out (a) 5v in pwm mode 5v in pfm mode 3.3v in pwm mode 3.3v in pfm mode 2.468 2.476 2.484 2.492 2.500 2.508 2.516 2.524 2.532 012345678 v out (v) i out (a) 5v in pwm mode 5v in pfm mode 3.3v in pwm mode 3.3v in pfm mode 3.28 3.29 3.30 3.31 3.32 3.33 3.34 3.35 3.36 012345678 v out (v) i out (a) 5v in pwm mode 5v in pfm mode
isl8018 fn7889 rev 0.00 page 11 of 21 september 30, 2015 figure 16. steady state operation at no load (pwm) f igure 17. steady state operation at no load (pfm) figure 18. steady state operation with full load figure 19. load transient (pwm) figure 20. load transient (pfm) figure 21. soft-start with no load (pwm) typical operating performance unless otherwise noted, operating conditions are: t a = +25c, v in = 5v, en = 3.3v, syncin = v in , l = 1h, c 1 = 2x22f, c 2 = 4x22f, v out = 1.8v, i out = 0a to 8a. (continued) phase 2v/div v out ripple 20mv/div il 1a/div 500ns/div phase 2v/div v out ripple 20mv/div il 1a/div 2s/div phase 2v/div v out ripple 20mv/div il 2a/div 500ns/div v out ripple 50mv/div il 2a/div 1ms/div v out ripple 50mv/div il 2a/div 1ms/div en 2v/div v out 1v/div il 2a/div pg 5v/div 5ms/div
isl8018 fn7889 rev 0.00 page 12 of 21 september 30, 2015 figure 22. soft-start at no load (pfm ) figure 23. soft-start with prebiased 1v figure 24. soft-start at full load figure 25. soft-discharge shutdown figure 26. steady state operation at no load with frequency = 2mhz figure 27. steady state operation at full load with frequency = 2mhz typical operating performance unless otherwise noted, operating conditions are: t a = +25c, v in = 5v, en = 3.3v, syncin = v in , l = 1h, c 1 = 2x22f, c 2 = 4x22f, v out = 1.8v, i out = 0a to 8a. (continued) en 2v/div v out 1v/div il 2a/div pg 5v/div 5ms/div en 5v/div v out 1v/div il 2a/div pg 5v/div 5ms/div en 2v/div v out 1v/div il 2a/div pg 5v/div 5ms/div en 2v/div v out 1v/div il 2a/div pg 5v/div 500s/div phase 5v/div il 1a/div sync 5v/div v out ripple 20mv/div 200ns/div phase 5v/div il 2a/div sync 5v/div v out ripple 20mv/div 200ns/div
isl8018 fn7889 rev 0.00 page 13 of 21 september 30, 2015 figure 28. steady state operation at no load with frequency = 4mhz figure 29. steady state operation at full load (pwm) with frequency = 4mhz figure 30. output short-circuit figure 31. output short-circuit recovery typical operating performance unless otherwise noted, operating conditions are: t a = +25c, v in = 5v, en = 3.3v, syncin = v in , l = 1h, c 1 = 2x22f, c 2 = 4x22f, v out = 1.8v, i out = 0a to 8a. (continued) phase 5v/div il 0.2a/div sync 5v/div v out ripple 20mv/div 100ns/div phase 5v/div il 2a/div sync 5v/div v out ripple 20mv/div 100ns/div phase 5v/div v out 1v/div il 5a/div pg 5v/div 10s/div phase 5v/div v out 1v/div il 5a/div pg 5v/div 2ms/div
isl8018 fn7889 rev 0.00 page 14 of 21 september 30, 2015 theory of operation the isl8018 is a step-down switching regulator optimized for battery-powered handheld applicat ions. the regulator operates at 1mhz fixed default switching frequency when fs is connected to vin. by connecting a resistor fr om fs to sgnd, the operating frequency may be adjusted from 500khz to 4mhz. unless forced and pwm is chosen (syncin pulled hi), the regulator will allow pfm operation and reduce switchin g frequency at light loading to maximize efficiency. in this conditio n, no load quiescent is typically 70a. pwm control scheme pulling the syncin high (>0.8v) forces the converter into pwm mode, regardless of output curr ent. the isl8018 employs the current-mode pulse width modulation (pwm) control scheme for fast transient response and pu lse-by-pulse current limiting. figure 3 shows the block diagram. the current loop consists of the oscillator, the pwm comparator, current sensing circuit and the slope compensation for the current loop stability. the slope compensation is 360mv/ts. current sense resistance, rt, is typically 0.11v/a. the control reference for the current loop comes from the error amplifier's (eamp) output. the pwm operation is initialized by the clock from the oscillator. the p-channel mosfet is turned on at the beginning of a pwm cycle and the current in the mosfet starts to ramp up. when the sum of the current amplifier cs a and the slope compensation reaches the control reference of the current loop, the pwm comparator eamp output sends a signal to the pwm logic to turn off the p-fet and turn on the n-channel mosfet. the n-fet stays on until the end of the pwm cycle. figure 32 shows the typical operating waveforms during the pwm operation. the dotted lines illustrate the sum of the slop e compensation ramp and the current-sense amplifier?s csa output. the output voltage is regulated by controlling the v eamp voltage to the current loop. the bandgap circuit outputs a 0.6v reference voltage to the voltage loop. the feedback signal comes from the vfb pin. the soft-start block only affects the operation during the start-up and will be discussed separately. the error amplifier is a transconductance amplifier that co nverts the voltage error signal to a current output. the voltage loop is internally compensated with the 55pf and 168k rc network. the maximum eamp voltage output is precisely clamped to 2.4v. skip mode pulling the syncin pin lo (<0.4v) forces the converter into pfm mode. the isl8018 enters a pulse-skipping mode at light load to minimize the switching loss by re ducing the switching frequency. figure 33 illustrates the skip mode operation. a zero-cross sensing circuit shown in figure 3 monitors the n-fet current for zero crossing. when 8 consecutive cycles of the inductor current crossing zero are detected, the regulator enters the skip mode. during the eight detecting cycles, the current in the inductor is allowed to become negative. the counter is reset to zero when the current in any cycle does not cross zero. once the skip mode is entered, the pulse modulation starts being controlled by the skip comparator shown in figure 33 . each pulse cycle is still synchronized by the pwm clock. the p-fet is turned on at the clock's rising edge and turn ed off when the output is higher than 1.5% of the nominal regulati on or when its current reaches the peak skip current limit value. then the induct or current is discharging to 0a and stays at zero. the internal clock is disabled. the output voltage reduces grad ually due to the load current discharging the output capacitor. when the output voltage drops to the nominal voltage, the p-fet will be turned on again at the rising edge of the internal clock as it repeats the previous operations. the regulator resumes normal pwm mode operation when the output voltage drops 1.5% below the nominal voltage. figure 32. pwm operation waveforms v eamp v csa duty cycle i l v out figure 33. skip mode operation waveforms clock i l v out nominal pfm current limit 0 8 cycles syncout pwm pfm nominal -1.5% pwm load current 0.8v nominal +1.5%
isl8018 fn7889 rev 0.00 page 15 of 21 september 30, 2015 frequency adjust the frequency of operation is fixed at 1mhz and internal compensation when fs is tied to vin. adjustable frequency ranges from 500khz to 4mhz via a simple resistor connecting fs to sgnd according to equation 1 : figure 34 is a graph of the measured frequency vs rt for a vin of 2.7v and 5.5v. synchronization control the isl8018 can be synchronized from 500khz to 4mhz by an external signal applied to the syncin pin. syncin frequency should be greater than 50% of internal clock frequency. the rising edge on the syncin triggers the rising edge of the phase pulse. make sure that the minimum on time of the phase node is greater than 140ns. syncout is a 250a current pulse si gnal that is triggered on the rising edge of the clock or syncin signal (whichever is greater in frequency). this drives other isl8018s and avoids system beat frequency effects. see figure 35 for more detail. the current pulse is terminated and syncout is discharged to 0v after 0.8v threshold is reached. syncout is 0v if the regulator operates at light pfm load. to implement time shifting betw een the master circuit to the slave, it is recommended to add a capacitor, c 13 as shown in figure 3 on page 5 . the time delay from syncout_master to syncin_slave as shown in figure 3 on page 5 is calculated in pf using equation 2 : where t is the desired time shift between the master and the slave circuits in ns. care must be taken to include pcb parasitic capacitance of ~3pf to 10pf. the maximum should be limited to 1/f sw -100ns to insure that syncout has enough time to discharge before the next cycle starts. figure 36 is a graph of the master to slave phase shift vs syncout capacitance for 1mhz switching operation. overcurrent protection the overcurrent protection is realized by monitoring the csa output with the ocp comparator, as shown in figure 3 on page 5 . the current sensing circuit has a gain of 0.11v/a, from the p-fet current to the csa output. when the csa output reaches a threshold set by iset, the ocp comparator is tripped to turn off the p-fet immediately. see ? analog specifications ? on page 6 of the ocp threshold for various iset configurations. the overcurrent function protects the switching converter from a shorted output by monitoring the current flowin g through the upper mosfet. upon detection of an overcurrent condition, the upper mosfet will be immediately turned off and will not be turned on again until the next switching cycle. upon de tection of the initial overcurrent condition, the overcurrent fault counter is set to 1. if, on the subsequent cycle, another overcu rrent condition is detected, the oc fault counter will be incremented. if there are 17 sequential oc fault detections, the regulator will be shut down under an overcurrent fault condition. an overcurrent fault condition will result in the regulator attempting to restart in a hiccup mode within the delay of eight soft-start periods. at the end of the eight soft-start wait period, the fault counters are reset and soft-start is attempted again. if the overcurr ent condition goes away during the delay of eight soft-start periods, the output will resume back into regulation point after hiccup mode expires. when an r t k ? ?? 220 10 3 ? f osc khz ?? ------------------------------ 14 C = (eq. 1) figure 34. frequency vs rt 0 700 1400 2100 2800 3500 4200 0 70 140 210 280 350 420 rt (k) fs (khz) v in = 2.7v v in = 5.5v c 13 pf ?? 0.333 t 20 C ?? ns ?? ? = (eq. 2) figure 35. synchronization waveforms phase1 clock1 syncout_m w/cap syncin_s phase2 0.8v 0.75v 20nsdelay 0 50 100 150 200 250 300 0 40 80 120 160 200 240 c 13 (pf) phase shift () figure 36. phase shift vs capacitance phase shift measurement phase shift calculation
isl8018 fn7889 rev 0.00 page 16 of 21 september 30, 2015 overcurrent condition happens at low v in , it is recommended to add more input capacitance, so the valley of v in is always above uvlo to maintain normal operation. negative current protection similar to overcurrent, the negative current protection is realized by monitoring the current across the low-side n-fet, as shown in figure 3 on page 5 . when the valley point of the inductor current reaches -3a for 4 consecutive cycles , both p-fet and n-fet are off. the 100 in parallel to the n-fet will activate discharging the output into regulation. the control will begin to switch when output is within regulation. the regulator will be in pfm for 20s before switching to pwm if necessary. pg pg is an open-drain output of a window comparator that continuously monitors the buck re gulator output voltage. pg is actively held low when en is low and during the buck regulator soft-start period. after 1ms delay of the soft-start period, pg becomes high impedance as long as the output voltage is within nominal regulation voltage set by vfb. when vfb drops 15% below or raises 0.8v above the nominal regulation voltage, the isl8018 pulls pg low. any fault co ndition forces pg low until the fault condition is cleared by attemp ts to soft-start. for logic level output voltages, connect an external pull-up resistor, r 1 , between pg and vin. a 100k resistor works well in most applications. uvlo when the input voltage is below the undervoltage lockout (uvlo) threshold, the regulator is disabled. soft start-up the soft start-up reduces the inrush current during the start-up. the soft-start block outputs a ramp reference to the input of the error amplifier. this voltage ramp limits the inductor current as well as the output voltage speed so that the output voltage rises in a controlled fashion. when vfb is less than 0.1v at the beginning of the soft-start, the switching frequency is reduced to 200khz so that the output can st art up smoothly at light load condition. during soft-start, the ic operates in the skip mode to support prebiased output condition. tie ss to sgnd for an internal soft-start of approximately 1ms. connect a capacitor from ss to sgnd to adjust the soft-start time. this capacitor, along with an internal 1.8a current source sets the soft-start interval of the converter, t ss . c ss must be less than 33nf to insure proper soft-start reset after fault condition. for proper use, do not prebias output voltage more than regulation point. figure 37 is a comparison between measured and calculated output soft-start time versus c ss capacitance. enable the enable (en) input allows the user to control the turning on or off of the regulator for purposes such as power-up sequencing. when the regulator is enabled, there is typically a 600s delay for waking up the bandgap refere nce and then the soft start-up begins. discharge mode (soft-stop) when a transition to shutdown mode occurs or the vin uvlo is set, the outputs discharge to gnd through an internal 100 switch. the discharge mode is disabled if ss is tied to an external capacitor. power mosfets the power mosfets are optimized for best efficiency. the on-resistance for the p-fet is typically 31m and the on-resistance for the n-fet is typically 19m . 100% duty cycle the isl8018 features 100% duty cycle operation to maximize the battery life. when the battery voltage drops to a level that the isl8018 can no longer maintain the regulation at the output, the regulator completely turns on the p-fet. the maximum dropout voltage under the 100% duty cycle operation is the product of the load current and the on-resistance of the p-fet. thermal shutdown the isl8018 has built-in thermal protection. when the internal temperature reaches +150c, the regulator is completely shut down. as the temperature drops to +125c, the isl8018 resumes operation by stepping through the soft-start. c ss ? f ?? 3.33 t ss s ?? ? = (eq. 3) 0 3 6 9 12 15 18 0 8 16 24 32 40 48 c ss (nf) v ss (ms) figure 37. soft-start time vs c ss ss (ms) measurement ss (ms) calculation
isl8018 fn7889 rev 0.00 page 17 of 21 september 30, 2015 power derating characteristics to prevent the regulator from exceeding the maximum junction temperature, some thermal analysis is required. the temperature rise is given by equation 4 : where pd is the power dissipated by the regulator and ja is the thermal resistance from the junc tion of the die to the ambient temperature. the junction temperature, t j , is given by equation 5 : where t a is the ambient temperature. for the tqfn package, the ja is 42 (c/w). the actual junction temperature should not exceed the absolute maximum junction temperature of +125c when considering the thermal design. applications information output inductor and capacitor selection to consider steady state and transient operations, isl8018 typically uses a 1h output induct or. the higher or lower inductor value can be used to optimize the total converter system performance. for example, for higher output voltage 3.3v application, in order to decrease the inductor current ripple and output voltage ripple, the output inductor value can be increased. it is recommended to set the ripple inductor current approximately 30% of the maximu m output current for optimized performance. the inductor ripple current can be expressed as shown in equation 6 : the inductor?s saturation current rating needs to be at least larger than the peak current. the isl8018 protects the typical peak current of 12a. the saturation current needs be over 16a for maximum output current application. the isl8018 uses an internal compensation network and the output capacitor value is dependent on the output voltage. the ceramic capacitor is recommended to be x5r or x7r. for high or low output voltage applications, use external compensation for better phase margin. output voltage selection the output voltage of the regulator can be programmed via an external resistor divider that is used to scale the output voltage relative to the internal reference voltage and feed it back to the inverting input of the error amplifier (refer to figure 2 on page 4 ). the output voltage programming resistor, r 2 , will depend on the value chosen for the feedback resistor and the desired output voltage of the regulator. the value for the feedback resistor is typically between 10k and 100k , as shown in equation 7 . if the output voltage desired is 0.6v, then r 3 is left unpopulated and r 2 is shorted. there is a le akage current from vin to phase. it is recommended to preload the output with 10a minimum. capacitance, c 3 , may be added to improve transient performance. a good starting point for c 3 can be determined by choosing a value that provides an 80khz corner frequency with r 2 . vset marginally adjusts vfb according to the ? analog specifications ? on page 6 . figure 39 is the recommended minimum output voltage setting vs operational frequency in orde r to avoid the minimum on-time specification. input capacitor selection the main functions for the input capacitor are to provide decoupling of the parasitic inductance and a filtering function to prevent the switching current flowing back to the battery rail. at least two 22f x5r or x7r cera mic capacitors are a good starting point for the input capacitor selection. t rise pd ??? ja ?? = (eq. 4) t j t a t rise + ?? = (eq. 5) 0 2 4 6 8 50 60 70 80 90 100 110 120 130 output current (a) temperature (c) 0.6v 3.3v 1.8v figure 38. derating curve vs temperature ? i v o 1 v o v in --------- C ?? ?? ?? ? lf sw ? -------------------------------------- - = (eq. 6) r 2 r 3 v o vfb ------------ 1 C ?? ?? = (eq. 7) figure 39. minimum v out vs frequency 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 frequency (mhz) v out (v) v in = 3.3v v in = 5v
isl8018 fn7889 rev 0.00 page 18 of 21 september 30, 2015 loop compensation design when there is an external resistor connected from fs to sgnd, the comp pin is active for external loop compensation. the isl8018 uses constant frequency peak current mode control architecture to achieve fast loop transient response. an accurate current sensing pilot device in parallel with the upper mosfet is used for peak current control si gnal and overcurre nt protection. the inductor is not considered as a state variable since its peak current is constant and the system becomes a single order system. it is much easier to design a type ii compensator to stabilize the loop than to implement voltage mode control. peak current mode control has an inherent input voltage feed-forward function to achieve g ood line regulation. figure 40 shows the small signal model of the synchronous buck regulator. figure 41 shows the type ii compensator and its transfer function is expressed as shown in equation 8 : where compensator design goal: high dc gain choose loop bandwidth f c less than 100khz gain margin: >10db phase margin: >40 the compensator design procedure is as follows: the loop gain at crossover frequency of f c has a unity gain. therefore, the compensator resistance r 6 is determined by equation 9 . where gm is the sum of the transconductance, g m , of the voltage error amplifier in each phase. compensator capacitor c 6 is then given by equation 10 . put one compensator pole at zero frequency to achieve high dc gain, and put another compensator pole at either esr zero frequency or half switching frequency, whichever is lower in equation 10 . an optional zero can boost the phase margin. ? cz2 is a zero due to r 2 and c 3 . put compensator zero 2 to 5 times f c . example: v in = 5v, v o = 1.8v, i o = 8a, f sw = 1mhz, r 2 = 200k , r 3 = 100k , c o =4x22f/3m , l = 1h, f c = 100khz, then compensator resistance r 6 : + 1:d + co rc -av(s) d h e (s) + k o v v in d l p + 1:d + rc ro r t f m t i (s) k o t v (s) v in ^ ^ ^ ^ ^ figure 40. small signal mo del of synchronous buck regulator r lp i l d ^ i in ^ i l ^ v comp - + r 6 v ref v fb vo gm v comp c 7 - + c 6 figure 41. type ii compensator c 3 r 2 r 3 a v s ?? v ? comp v ? fb ---------------- - gm r 3 ? c 6 c 7 + ?? r 2 r 3 + ?? ? -------------------------------------------------------- 1 s ? cz1 ------------ - + ?? ?? 1 s ? cz2 ------------ - + ?? ?? s1 s ? cp1 ------------- + ?? ?? 1 s ? cp2 ------------- + ?? ?? -------------------------------------------------------------- - = = (eq. 8) ? cz1 1 r 6 c 6 -------------- - ? cz2 1 r 2 c 3 -------------- - = ? cp1 ? c 6 c 7 + r 6 c 6 c 7 ---------------------- - ? cp2 r 2 r 3 + c 3 r 2 r 3 ---------------------- - = ? = , = r 6 2 ? f c v o c o r t gm v fb ? --------------------------------- - 5.76 3 ? 10 f c v o c o ? == (eq. 9) c 6 r o c o r 6 -------------- - v o c o i o r 6 -------------- - c 7 max r c c o r 6 -------------- - 1 ? f s r 6 --------------- - (, ) = , = = (eq. 10) c 3 1 ? f c r 2 --------------- - = (eq. 11) r 6 5.76 3 ? 10 100khz 1.8v 88 ? f ? ? ? 91.2k ? == (eq. 12) c 6 1.8v 88 ?? f 8a 90.9k ? ? -------------------------------- 217pf = = (eq. 13) c 7 max 3m ? 88 ? f ? 90.9k ? -------------------------------- - 1 ? 1mhz 90.9k ? ?? ? ------------------------------------------------- - (, ) 2.9pf 3.5pf (, ) = = (eq. 14)
isl8018 fn7889 rev 0.00 page 19 of 21 september 30, 2015 it is also acceptable to use the closest standard values for c 6 and c 7 . there is approximately 3pf parasitic capacitance from v comp to gnd. therefore, c 7 is optional. use c 6 = 220pf and c 7 = open. use c 3 = 15pf. note that c 3 may increase the loop bandwidth from previous estimated value. figure 42 on page 19 shows the simulated voltage loop gain. it is shown that it has a 125khz loop bandwidth with a 45 phase margin and 10db gain margin. it may be more desirable to achieve an increased phase margin. this can be accomplished by lowering r 6 by 20% to 30%. pcb layout recommendation the pcb layout is a very important converter design step to make sure the designed converter works well. for isl8018, the power loop is composed of the output inductor l?s, the output capacitor c out , the phase?s pins and the pgnd pin. it is necessary to make the power loop as small as possible and the connecting traces among them should be direct, short and wide. the switching node of the converter, the phase pins and the traces connected to the node are very noisy, so keep the voltage feedback trace away from these noisy traces. the input capacitor should be placed as close as possible to th e vin pin and the ground of the input and output capacitors should be connected as close as possible. the heat of the ic is mainly dissipated through the thermal pad. maximizing the copper area connected to the thermal pad is preferable. in addition, a solid ground plane is helpful for better emi performance. it is recommended to add at least 5 vias ground connection within the pad for the best thermal relief. c 3 1 ? 100khz 200k ? ? ------------------------------------------------ = 16pf = (eq. 15) -200 -150 -100 -50 0 50 100 150 -60 -40 -20 0 20 40 60 80 figure 42. simulated loop gain 100 1k 10k 100k 1m frequency (hz) 100 1k 10k 100k 1m frequency (hz) phase () gain (db)
fn7889 rev 0.00 page 20 of 21 september 30, 2015 isl8018 intersil products are manufactured, assembled and tested utilizing iso9001 quality systems as noted in the quality certifications found at www.intersil.com/en/suppor t/qualandreliability.html intersil products are sold by description on ly. intersil may modify the circuit design an d/or specifications of products at any time without notice, provided that such modification does not, in intersil's sole judgment, affect the form, fit or function of the product. accordingly, the reader is cautioned to verify that datasheets are current before placing orders. information fu rnished by intersil is believed to be accu rate and reliable. however, no responsib ility is assumed by intersil or its subsidiaries for its use; nor for any infrin gements of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of intersil or its subsidiaries. for information regarding intersil corporation and its products, see www.intersil.com for additional products, see www.intersil.com/en/products.html ? copyright intersil americas llc 2015. all rights reserved. all trademarks and registered trademarks are the property of their respective owners. about intersil intersil corporation is a leading provider of innovative power ma nagement and precision analog so lutions. the company's product s address some of the largest markets within the industrial and infrastr ucture, mobile computing and high-end consumer markets. for the most updated datasheet, application notes, related documentatio n and related parts, please see the respective product information page found at www.intersil.com . you may report errors or suggestions for improving this datasheet by visiting www.intersil.com/ask . reliability reports are also av ailable from our website at www.intersil.com/support revision history the revision history provided is for informational purposes only and is believed to be accurate, but not warranted. please go t o web to make sure you have the latest rev. date revision change september 30, 2015 fn7889.0 initial release.
isl8018 fn7889 rev 0.00 page 21 of 21 september 30, 2015 package outline drawing l20.3x4 20 lead quad flat no-lead plastic package rev 1, 3/10 typical recommended land pattern detail "x" top view bottom view side view located within the zone indica ted. the pin #1 indentifier may b e unless otherwise specified, t olerance : decimal 0.05 tiebar shown (if present) is a non-functional feature. the configuration of t he pin #1 identifier is optional, but mus t be between 0.15mm and 0.30mm from the terminal tip. dimension applies to the metalliz ed terminal and is measured dimensions in ( ) for reference only. dimensioning and tolerancing conform to amse y14.5m-1994. 6. either a mold or mark feature. 3. 5. 4. 2. dimensions are in millimeters. 1. notes: 0.10 m c a b mc 0.05 0.15 0.08 c 0.10 c a b c c 4.00 3.00 20x 0.400.10 2.65 1.65 0.25 0.50 (2.80) (1.65) +0.10 -0.15 +0.10 -0.15 +0.05 -0.07 20x a a 4 (4x) seating plane 0.9 0.10 5 0.2 ref 0.05 max. see detail "x" 0.00 min. (c 0.40) 1 20 17 16 11 6 10 7 (3.80) (2.65) (20 x 0.25) (20 x 0.60) (16 x 0.50) 16x view "a-a" pin 1 index area pin 1 index area 6 6

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