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lx2750 microsemi analog mixed signal group 1 rev. 1.0a 07/14/10 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 typical application description the lx2750 controller ic is a compact synchronous buck controller ic with 16 lead mlpq package de- signed for step-down dc to dc converter applications. selectable feedforward voltage mode control or con- stant on time control provides fast dynamic response. selectable diode emulation mode greatly improves the light load efficiency. the lx2750 controller is optimized to convert single supply 12v bus voltage to as low as 0.8v output voltage. an internal regulator converts bus voltage to 5v, which provides voltage supply to inter- nal logic and driver circuit. the lx2750 employs pro- grammable loss-less current limiting by sensing the rdson of synchronous mosfet followed by hiccup feature. feedback under voltage also triggers hiccup. internal uvlo keeps the controller off until the bus supply voltage exceeds 9v where internal digital soft starts get initiated to ramp up output. the lx2750 em- ploys nmos ldo controller. other features include: 5v gate drive for hdrv signal, 12v gate drive for ldrv signal, programmable frequency, adaptive deadband control. n single input 12v bus voltage n excellent dynamic response with selectable feedforward voltage mode control or constant on time control n diode emulation mode available n programmable switching frequency up to 2mhz n internal digital soft start function n programmable over current protection triggers hiccup n nmos ldo controller available n fb uvlo followed by hiccup feature in both controllers n 5v high side driver and 12 v low side driver n pb-free and rohs compliant ordering information features single input supply pwm controller with ldo controller applications n graphic card on board converters n on board dc to dc such as 12v to 3.3v, 2.5v or 1.8v n set top box and lcd display n asic power supplies production data sheet figure1 - typical application of lx2750 device temperature package frequency pb-free lx2750clq 0 to 70 o c 3x3 mlpq-16l 200khz to 2mhz yes pb free product l x 2 7 5 0 1 2 +1.8v@8a vout1 15 14 13 11 bst fb comp sw hdrv ldrv vin 4 3 +1.1v vout2 ldo_fb ldo_drv 7 mode +12v vin1 17 8 vcc 10 gnd(pad) 16 rt connected to gnd constant on time mode connected to 5vreg voltage mode pgood 12 6 vref_oc refin gpio 5 fccm 9 connected to gnd diode emulation mode connected to 5vreg synchronous mode note: available in tape & reel. append the letters "tr" to the part number. (i.e. lx2750clq-tr)
lx2750 microsemi analog mixed signal group 2 rev. 1.0a 07/14/10 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 absolute maximum ratings 5vreg to gnd & bst to sw voltage ................ -0.3v to 6v vin, ldo_drv to gnd ...................................... -0.3v to 16v bst,hdrv to gnd voltage .............................. -0.3v to 21v sw to gnd ....................................................... -2v to 16v ldrv to gnd .................................................... -0.3v to vin+0.3v all other pins ..................................................... -0.3v to vcc+0.3v storage temperature range ............................... -65 o c to 150 o c operating junction temperature range ...............-40 o c to 125 o c esd susceptibility .............................................. 1000v caution: stresses above those listed in "absolute maximum ratings", may cause permanent damage to the device. this is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. package information 3x3 16-lead plastic mlpq electrical specifications unless otherwise specified, these specifications apply over vin=12v and t a = 0 to 70 o c . typical values refer to t a = 25 o c . 9 10 11 12 4 3 2 1 fb rt ldo_drv ldo_fb fccm vcc ldrv pgood 8 7 6 5 vin mode refin vref_oc 16 15 14 13 hdrv comp bst sw gnd 17 o ja cw q?46/ parameter sym test condition min typ max units refout_oc voltage refout_oc voltage v ref 2.45 2.5 2.55 v accuracy v in from 10v to 16v -0.3 0.3 % supply voltage(vin) v in voltage range v in 10 16 v input voltage current(static) no switching,comp=0.8v 7 ma input voltage current (dynamic) switching with hdrv and ldrv open,comp=1.8v 9 ma
lx2750 microsemi analog mixed signal group 3 rev. 1.0a 07/14/10 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 n parameter sym test condition min typ max units vin uvlo v in -threshold v in _uvlo v in rising 9 v v in -hysteresis v in _hyst v in falling 8 v 5v reg 5vreg output no switching 5.4 v 5vreg max current 30 50 ma ss tss_pwm f s =350khz,mode=5v 5.2 ms tss_con f s =350khz,mode=0v 1.3 ms oscillator (rt) frequency f s rt=110k,mode=5v 245 300 359 khz ramp-feedforward gain v ramp 0.1 v/v ramp offset 1 v max duty cycle f s =300khz 80 % min off time 560 ns min controlable on time 200 ns rt disable threshold 0.3 v error amplifiers open loop gain (note1) 80 db gain bandwidth (note1) 10 mhz input bias current ib 1 100 na max sourcing current fb=0.7v, comp>=3v 3 ma max sinking current fb=0.9v,comp<=0.3v 0.4 ma comp high voltage fb=0.7v, source 80ua 4.4 v comp low voltage fb=0.9v, sink 40ua 0.1 v sw zero cross comparator offset voltage -2 mv high side driver output impedance , sourcing current (note1) r source (hdrv) bst to sw=5v, i=200ma 1 ohm output impedance , sinking current (note1) r sink (hdrv) bst to sw=5v, i=200ma 0.8 ohm low side driver output impedance, sourcing current (note1) r source (ldrv) pvcc=12v 6 ohm output impedance, sinking current (note1) r sink (ldrv) pvcc=12v 2 ohm mode,fccm threshold high threshold 2 v low threshold 0.8 v internal schottky diode forward voltage drop forward current=20ma 450 mv power good threshold voltage as % of vref fb ramping up 85 % hysteresis 5 % fbuvlo feedback uvlo threshold percent of nominal 60 % soft start time
lx2750 microsemi analog mixed signal group 4 rev. 1.0a 07/14/10 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 note note1: design guaranteed. parameter sym test condition min typ max units ldo controller open loop gain(note1) 100 db gain bandwidth(note1) 2 mhz fb pin- bias current 1 100 na ldo fb voltage 0.772 0.8 0.828 v ldo fb uvlo percent of nominal 60 % high output voltage vin=12v,ldofb=0.7v, source 1.4ma 11.5 v low output voltage ldofb=0.9v,sink 1.4ma 0.4 v max sourcing current ldofb=0.7v, ldodrv>8v 2 ma min sinking current ldofb=0.9v, ldodrv<1v 8 ma
lx2750 microsemi analog mixed signal group 5 rev. 1.0a 07/14/10 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 pin descriptions pin symbol pin description this pin is internal 5v regulator output and supplies the internal 5v bias circuit. a high freq 1uf ceramic capacitor is recommended to connect this pin to ground. this pin supplies voltage to high side fet driver. a high freq minimum 0.1uf ceramic capacitor is placed as close as possible to and connected to this pin and sw pin. ground pin. this pin is the error amplifiers inverting input. this pin is connected via resistor divider to the output of the switching regulator to set the output dc voltage. this pin is the output of the error amplifier and together with fb pin is used to compensate the voltage control feedback loop. this pin is connected to source of high side fets and provide return path for the high side driver. high side gate driver output. low side gate driver output. voltage supply for the internal 5v regulator, ldo controller and low side driver. oscillator's frequency can be set by using an external resistor from this pin to gnd. pulling this pin down below 0.3v shuts down both controllers. ldo controller feedback input. this pin is connected via resistor divider to the output of the ldo to set the output dc voltage. ldo controller output. this pin is controlling the gate of an external nch mosfet. the maximum rating of this pin is 16v. connecting this pin to 5vreg voltage control mode will be chosen. connecting this pin to ground, constant on time control mode will be chosen. connecting this pin to 5vreg, synchronous mode will be chosen. connecting this pin to ground, diode emulation mode will be chosen, ldrv will be off when inductor current becomes negative current. reference input voltage for error amplifier. 2.5v external reference. ocp trigger level is set by connect resistor from this pin to ground. pgood indicator for switching regulator. it requires a pull up resistor to vcc or lower voltage. when fb pin reaches 85% of the reference voltage pgood transitions from lo to hi state. vcc bst gnd fb comp sw hdrv ldrv vin rt ldo_fb ldo_drv mode fccm refin vref_oc pgood
lx2750 microsemi analog mixed signal group 6 rev. 1.0a 07/14/10 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 block diagram figure 2 - simplified block diagram of the lx2750 vin uvlo por ss_done ldo_fb ldo_drv 0.3v bias generator 1.25v 0.8v bst hdrv sw ldrv 9/8 rt gnd vcc hiccup hiccup reset dominant fet drivers latchout logic vin start start fb 60%*vp ss_half_done 60%*0.8v por r vin mode mode selection voltage mode constant on time fccm mode selection synchronous mode diode emulation mode vref_oc ldo pgood pgood fb comp osc digital start up start start clk hdin internal rt fb dis_ea pwm/pfm control core iff comp rt 9k ldopor ldo amplifier ldopor ss_dac refin
lx2750 microsemi analog mixed signal group 7 rev. 1.0a 07/14/10 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 figure 3 - demo board schematic hdrv ldoin r33 40.2k ldoout m8 2n7002 r34 20k j1 jp 1 2 r28 op m3 op 1 4 8 5 6 7 2 3 r29 op m4 ntd60n02r jp1 jumper3/200 1 2 3 0 jp2 jumper3/200 1 2 3 pgood gnd ldrv r2 2.15 c8 1200p gpio1 c28 10uf,x5r,6.3v) r32 0 bus l1 rl-8250-4-1r0m jp3 op 1 2 0 r35 20k m5 op m6 ntd70n03r l12 r8 0 h12 r9 op r19 0 r24 op d1 op m2 op m1 ntd60n02r mod=vcc pwm mod=gnd constant on time control jp4 jumper2/100 1 2 r21 30k d2 op c14 op r6 op c29 1n c10 22u r36 op tp1 comp l11 u1 lx2750_mlpq16 comp 1 fb 2 ldpdrv 3 ldofb 4 refin 5 ref_oc 6 vin 7 mode 8 fccm 9 5vcc 10 ldrv 11 pgood 12 sw 13 hdrv 14 bst 15 rt 16 gnd 17 r11 68.1k c3 10uf,16v l2 short r12 32.4k r22 32k sw swvout c22 1n c9 2x(22uf,x5r,6.3v) r23 8k c23 1n c25 1n r20 op r16 1k bus h11 r17 1k q1 mmbt3904 c27 22u r26 op m7 op jvout1 2 3 4 5 1 c30 0.1u 5vcc 0 c5 1u r10 op r1 100k c18 220u,16v c7 2r5sepc820m tp3 pgood c1 16sepc270 l11 h11 0 vbus1 l12 h12 m12 op 1 2 3 4 5 6 7 8 9 m11 op 1 2 3 4 5 6 7 8 9 m13 op 1 2 3 4 5 6 7 8 9 m14 op 1 2 3 4 5 6 7 8 9 sw 5vcc ldo in r27 0 5vcc c11 1.8n r5 2.6k sw vout r30 op r3 95.3k gpio0 c12 4.7n c13 120p r7 8k sw tp2 sd r14 16k 5vcc jvout 2 3 4 5 1 c21 0.1u bus tp4 5vcc c6 0.47u,16v 0 r13 1 c4 op ldo out r31 op 0 r15 10k 0 vbus1 5vcc c26 0.1u 0 r18 0 c24 0.1u
lx2750 microsemi analog mixed signal group 8 rev. 1.0a 07/14/10 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 bill of materials item quantity reference part 1 1 c1 16sepc270 2 1 c3 10uf,16v 3 1 c5 1u 4 1 c6 0.47u,16v 5 1 c7 2r5sepc820m 6 1 c8 1200p 7 2 c9 22uf,x5r,6.3v 8 2 c10,c27 22uf,x5r,6.3v 9 1 c11 1.8n 10 1 c12 4.7n 11 1 c13 120p 12 1 c18 220u,16v 13 4 c21,c24,c26,c30 0.1u 14 4 c22,c23,c25,c29 1n 15 1 c28 10uf,x5r,6.3v 16 1 l1 rl-8250-4-1r0m 17 2 m1,m4 ntd60n02r 18 1 m6 ntd70n03r 19 1 m8 2n7002 20 1 q1 mmbt3904 21 1 r1 100k 22 1 r2 2.15 23 1 r3 95.3k 24 1 r5 2.6k 25 2 r7,r23 8k 26 5 r8,r18,r19,r27,r32 0 27 1 r11 68.1k 28 1 r12 32.4k 29 1 r13 1 30 1 r14 16k 31 1 r15 10k 32 2 r16,r17 1k 33 1 r21 30k 34 1 r22 32k 35 1 r33 40.2k 36 2 r34,r35 20k 37 1 u1 lx2750_mlpq16
lx2750 microsemi analog mixed signal group 9 rev. 1.0a 07/14/10 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 fig. 8 sw dynamic response when mode=5v,fccm=5v(ch1 sw vout ac 50mv/ div, ch4 inductor current 5a/div) fig.6 sw vout ripple when mode=5v (ch1 sw vout ripple 50mv/div, ch3 sw 10v/div, ch4 inductor current 5a/div) fig.5 use rt pin to turn on and off (ch1 ldo vout 1v/div, ch2 sw vout 1v/div, ch3 signal on tp2 5v/div) demoboard waveforms fig.4 startup when mode=5v (ch1 sw 5v/div, ch2 sw vout 1v/div) fig.7 sw output short(ch1 sw 10v/div, ch2 sw vout 1v/div, ch4 inductor current 10a/ div) fig. 9 sw dynamic response when mode=0v,fccm=5v(ch1 sw vout ac 50mv/ div, ch4 inductor current 5a/div)
lx2750 microsemi analog mixed signal group 10 rev. 1.0a 07/14/10 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 10 100 1000 10000 output current(ma) efficiency(%) fccm=high fccm=low 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100 1000 10000 output current(ma) efficiency(%) fccm=high fccm=low demoboard waveforms(cont') fig. 10 sw dynamic response when mode=0v,fccm=0v, load from 3ma to 10a(ch1 sw vout ac 20mv/div, ch4 inductor current 5a/div) fig. 11 sw dynamic response when mode=5v,fccm=0v, load from 8ma to 10a(ch1 sw vout ac 50mv/div, ch4 inductor cur- rent 5a/div) fig. 12 ldo dynamic response when ldo load from 0.1a to 1a (ch1 ldodrv 1v/div, ch2 ldo vout ac 100mv/div, ch4 output current 1a/div) fig. 13 line transient when mode=5v(ch1 vin 5v/div, ch4 sw vout ac 50mv/div) fig. 14 efficiency when mode=5v fig. 15 efficiency when mode=0v
lx2750 microsemi analog mixed signal group 11 rev. 1.0a 07/14/10 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 mlpq 16 pin 3 x 3 package outline dimensions symbol name min max min max a 0.700 0.800 0.028 0.031 a1 0.000 0.050 0.000 0.002 a3 b 0.180 0.300 0.007 0.012 d 2.950 3.050 0.116 0.120 d2 1.600 1.750 0.063 0.069 e 2.950 3.050 0.116 0.120 e2 1.600 1.750 0.063 0.069 e l 0.325 0.450 0.013 0.018 m 0.203ref 0.50bsc 1.5ref dimensions in inches 0.008ref 0.50bsc 0.059ref dimensions in millimeters

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