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MP4700 high-brightness, bcm, low side buck white led driver MP4700 rev. 1.0 www.monolithicpower.com 1 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. the future of analog ic technology description the MP4700 is a high-efficiency step-down converter designed to drive high-brightness light emitting diodes. the MP4700 drives an external mosfet in boundary conduction mode, which features no reverse recovery loss in the freewheeling diode and soft turn-on with zero-current and valley voltage for the power mosfet that improves efficiency and minimizes the inductor value and size. the boundary conduction control mode regulates the led current by sensing the mosfet peak current through an external resistor. its low 300mv feedback voltage reduces power loss and improves efficiency. the MP4700 implements pwm dimming to the led current. protection features include output short protection, under-voltage lockout for the ic input voltage and bus input voltage, a limited maximum switching frequency, and thermal shut down. features ? 8v-to-18v input voltage ? constant-current led driver ? power mosfet zero-current turn-on ? no freewheeling diode reverse recovery issues ? high efficiency and reliability in boundary conduction mode ? low 1ma operation current ? pwm dimming control ? hiccup short circuit protection ? uvlo for bus input voltage ? input uvlo, thermal shutdown ? maximum frequency limited to 160khz ? available in soic8 package applications ? led backlighting for tv and monitor ? dc/dc or ac/dc led driver applications ? general illumination ? industrial lighting ? automotive/ decorative led lighting a ll mps parts are lead-free and adhere to the rohs directive. for mps green status, please visit mps website under quality assurance. ?mps? and ?the future of analog ic technology? are registered trademarks of monolithi c power systems, inc. typical application
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 2 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. ordering information part number* package top marking MP4700gs soic8 MP4700 *for tape & reel, add suffix ?z (eg. MP4700gs-z) package reference absolute maxi mum ratings (1) vin .................................................. -0.3v to 20v vcc, drv ....................................... -0.3v to 11v pwm, inuv, cs ............................ -0.3v to 6.5v continuous power dissipation ....... (t a =25c) (2) soic8???????????????..1.3w junction temperature ............................... 150c lead temperature .................................... 260c storage temperature ............... -55c to +150c recommended operating conditions (3) vin ...................................................... 8v to 18v vcc, drv?????????. -0.3v to 10.5v operating junct. temp(t j ) ...... ?40c to +125c thermal resistance (4) ja jc soic8 ..................................... 96 ...... 45 ... c/w notes: 1) exceeding these ratings may damage the device. 2) the maximum allowable power dissipation is a function of the maximum junction temperature t j (max), the junction-to- ambient thermal resistance ja , and the ambient temperature t a . the maximum allowable continuous power dissipation at any ambient temperature is calculated by p d (max) = (t j (max)- t a )/ ja . exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. internal thermal shutdown circuitry protects the device from permanent damage. 3) the device is not guaranteed to function outside of its operating conditions. 4) measured on jesd51-7, 4-layer pcb.
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 3 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. electrical characteristics v in =12vdc, v pwm = 5v, no load on pin drv, t a = +25c, unless otherwise noted. parameters symbol condition min typ max units input voltage v in dc voltage at pin vin 8 18 v input supply current (quiescent) i inqs v pwm = 0v 0.6 ma input supply current (operation) i inrun v pwm = 5 v 0.78 ma vcc voltage vcc v in =10v (v in <12v) 7.5 8.5 9.5 v vcc peak voltage vcc h v in =18v (v in >12v) 9.8 v vcc valley voltage vcc l v in =18v (v in >12v) 9 v vcc uvlo vcc uvlo v in rising with a dc input 7 7.4 7.8 v vcc uvlo hysteresis vcc h y s v in falling with a dc input 1 v pwm input high threshold v pwmh v pwm rising 1.5 v pwm input low threshold v pwml v pwm falling 0.75 v pwm pull-up current i pwm pull up v pwm =0v 10.6 ua bus input voltage uvlo threshold v inuv_th_rising bus input voltage rising 1.15 1.2 1.25 v bus input voltage uvlo hysteresis v inuv_hys bus input voltage falling 50 86 120 mv pwm dimming on propagation delay pwmon_pd pwm rising edge to drive rising edge 1.3 2 us pwm dimming off propagation delay pwmoff_pd pwm falling edge to drive falling edge 230 350 ns cs pin reference voltage v ref -40c t a +85c 270 302 330 mv cs pin reference voltage v ref t a =+25c 285 302 315 mv leading edge blanking time leb 200 320 450 ns cs bias current i cs v cs =0.3v -0.5 0 ? on _ min 320 450 ns max switching frequency f sw max 160 khz over-temperature protection threshold t otp 150 c over-temperature protection threshold hysteresis t otp_hys 30 c output short shut down time shut-down 2.8 ms
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 4 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. pin functions pin # name description 1 inuv input bus voltage uvlo. sense with a voltage divider. 2 pwm pwm dimming input. connect directly to the pwm dimming signal. apply a high voltage or leave open for no applied dimming control. 3 gnd ground. 4 vin input supply. apply a voltage in the range of 8v to 18v. 5 vcc internal regulated supply voltage output. must be locally bypassed. provides power for ic logic and to drive the external mosfet. 6 tst test. connect to gnd. 7 drv external mosfet drive signal. also detects the zero current crossing. 8 cs led current sense input. connect to the curr ent sense resistor that programs the led current.
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 5 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical characteristics inuv_uvlo_hys (v) inuv_uvlo_lh (v) cs pin current vs. temperature v cs =0.3v input bus voltage uvlo threshold vs. temperature vcc uvlo vs. temperature vcc voltage vs. temperature v in =10v input bus voltage uvlo hysteresis vs. temperature pwm low high threshold vs. temperature cs reference volatage vs. temperature pwm input high threshold vs. temperature pwm pull up current vs. temperature 8.000 9.000 10.000 11.000 12.000 -50 -30 -10 10 30 50 70 90 110 130 -0.500 -0.400 -0.300 -0.200 -0.100 0.000 -50 -30 -10 10 30 50 70 90 110 130 1.100 1.150 1.200 1.250 1.300 -50 -30 -10 10 30 50 70 90 110 130 0.050 0.060 0.070 0.080 0.090 0.100 0.110 -50 -30 -10 10 30 50 70 90 110 130 7.200 7.250 7.300 7.350 7.400 7.450 -50 -30 -10 10 30 50 70 90110 130 vcc_uvlo_lh (v) 8.100 8.150 8.200 8.250 8.300 8.350 8.400 8.450 8.500 8.550 -50 -30 -10 10 30 50 70 90110 130 vcc_dc_reg_10v (v) 1.200 1.250 1.300 1.350 1.400 1.450 1.500 -50 -30 -10 10 30 50 70 90110 130 dim_pwm_input_h (v) 0.700 0.720 0.740 0.760 0.780 0.800 -50 -30 -10 10 30 50 70 90110 130 dim_pwm_input_l (v) 299.000 299.500 300.000 300.500 301.000 301.500 302.000 302.500 303.000 303.500 -50 -30 -10 10 30 50 70 90110 130
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 6 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical characteristics (continued) pwm dimming off propagation delay time vs. temperature leading edge blanking time vs.temperature maximum off time vs. temperature pwm dimming on propagation delay time vs. temperature 1200.000 1250.000 1300.000 1350.000 1400.000 1450.000 1500.000 -50 -30 -10 10 30 50 70 90 110130 0.000 50.000 100.000 150.000 200.000 250.000 300.000 -50 -30 -10 10 30 50 70 90 110 130 315.000 320.000 325.000 330.000 335.000 340.000 345.000 -50 -30 -10 10 30 50 70 90 110 130 2.400 2.500 2.600 2.700 2.800 2.900 -50 -30 -10 10 30 50 70 90110 130
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 7 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical performanc e characteristics v in =12.5vdc, v pwm = 5v, v bus =220v, v led =180v, i led =0.22a, t a = +25c, unless otherwise noted. v cc 2v/div. v in 2v/div. v drv 5v/div. i led 100ma/div. v cc 2v/div. v in 2v/div. v drv 5v/div. i led 100ma/div. ic v in turn on ic v in turn off v cc 2v/div. v cs 200mv/div. v drv 5v/div. i led 100ma/div. v cc 2v/div. v cs 200mv/div. v drv 5v/div. i led 100ma/div. v cc 2v/div. v bus 50v/div. v drv 5v/div. i led 100ma/div. pwm turn on v in = 12.5v pwm turn off v in = 10.7v v bus turn on v in = 12.5v led current (a) input bus voltage (v) input bus voltage (v) 200 205 210 215 220 225 230 180 200 220 240 260 280 300 97 97.2 97.4 97.6 97.8 98.0 98.2 98.4 98.6 98.8 200 220 240 260 280290 0 0.05 0.1 0.15 0.2 0.25 0 20 40 60 80 100 120 0 0.5 1 1.5 2 2.5 0.00 0.20 0.40 0.60 0.80 1.00 1.20
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 8 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical performanc e characteristics (continued) v in =12.5vdc, v pwm = 5v, v bus =220v, v led =180v, i led =0.22a, t a = +25c, unless otherwise noted. v cc 2v/div. v bus 50v/div. v drv 5v/div. i led 100ma/div. v pwm 2v/div. v cs 200mv/div. v drv 10v/div. i led 100ma/div. v pwm 2v/div. v cs 200mv/div. v drv 10v/div. i led 100ma/div. v pwm 2v/div. v cs 200mv/div. v drv 10v/div. i led 20ma/div. v pwm 2v/div. v cs 200mv/div. v drv 10v/div. i led 200ma/div.
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 9 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. functional block diagram cin drive rs c1 vcc vin vbus cs gnd filter and leb=320ns thermal protection thermal protection inuv 1.2v 50k zero-i detection circuit pwm 2.8ms max off time control 160khz max frequency control driver driver uvlo vref output short protection output short protection control and protection circuit r inuv_h r inuv_l ldo figure 1: block diagram
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 10 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. operation internal regulator the MP4700 uses a low dropout (ldo) regulator to supply the ic. use a dc voltage in the range of 8v to 18v to power the ic. the internal ldo regulator maintains the vcc voltage at 8.4v when the input voltage is less than 12v. the vcc pin requires a ceramic bypass capacitor. when the input voltage exceeds 12v, the ldo regulator switches to switch-controlled current source mode. the vcc voltage charges to its peak voltage (9.8v) and then the current source stops. after the vcc voltage decreases to its valley voltage (9v), the current source turns on again. this switch-controlled current source mode reduces the ldo power consumption and improves efficiency. led current regulation and valley detection in floating-buck-converter configuration, as shown in the typical application circuit, the MP4700 controls the mosfet (q1) using peak current control. the cs pin senses the peak current through a resistor (r sense ) to regulate the current to: l _ peak sense 302mv i r ? in normal operation, the MP4700 turns on q1 when the current in the freewheeling diode goes to zero. as a result, the average led current is: led sense 302mv i 2r ? the zero-current detection is realized at the drv pin by sensing the mosfet drain dv/dt current through the q1?s miller capacitor. when the current through the freewheeling diode goes to zero, the q1 drain voltage (v sw ) drops from v bus to (v bus ? v out ) and oscillates thanks to the inductor and the parasitic capacitors. when v sw drops to the minimum value, the dv/dt current through the miller capacitor rises from negative to zero. at this point, the MP4700 turns on q1 as the inductor current goes to zero and the q1 drain voltage is at its minimum. the MP4700 controls the buck converter in current-boundary-conduction mode. to improve zero current detection, add a 10pf capacitor between the q1 drain and source . add a capacitor (c out ) in parallel to the led string to reduce the current ripple. boundary operation mode minimizes the q1 turn-on loss and eliminates the freewheeling diode?s reverse recovery loss to reduce passive components? size requirements at high switching frequencies. furthermore, the required inductance value is already small, further reducing the inductor size. brightness dimming control the MP4700 employs pwm dimming to control the led current. use a 100hz-to-2khz pwm signal. pwm input high triggers ic switching. pwm input low turns off the ic. for applications that do not need pwm dimming control, apply a high voltage on the pwm pin or leave the pwm pin open. frequency setting and inductor design in case the zero-current detection circuit fails? which can happens at start-up during an output short condition with a large output capacitor? applying a maximum off time of about 2.8ms ensures that the MP4700 continues to operate and the prevents short current runaway. the MP4700 has a maximum switching frequency of 160khz to avoid extreme circuit losses and ensure better emi performance. if the converter reaches the maximum frequency, it will operate in discontinuous current conduction mode. avoid this operation mode since the led current is out of regulation. inductor design is critical to to ensure that the switching frequency (f s ) is within the 30khz to 160khz range. bus out out s led bus (v v ) v 1 l f2i v ?? ?? ?? , where v bus is the input voltage of the buck converter, and v out is the led voltage.
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 11 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. hiccup output-short protection if the entire led string is shorted, v out is zero. due to the minimal on time limit, the inductor current will be out of regulation. the MP4700 can detect this failure and shut down for about 2.8ms, and then re-tries the operation. this hiccup protection can eliminate thermal issues due to a short-circuit current, and also maintain normal operation if the protection is mis- triggered. input-bus - voltage under-voltage lockout (uvlo) protection the MP4700 implements uvlo protection for the input bus voltage. the inuv pin senses the input bus voltage through a voltage divider. the ic is locked out until the input bus voltage rises so that the inuv voltage pin exceeds its uvlo threshold. this uvlo function protects against a low input bus voltage. for best results, set the input bus voltage uvlo point over 1.1 times the output led voltage. set the input bus uvlo as follows: inuv _ h bus uvlo inuv _ l inuv _ th r v_ 1 rv ?? where v inuv_th =1.2v is the inuv pin threshold voltage. vcc under-voltage lockout (uvlo) protection under-voltage lockout (uvlo) protects the chip from operating at an insufficient supply voltage. the uvlo rising threshold is about 7.4v while its falling threshold is a consistent 6.4v. thermal shutdown protection an accurate temperature protection prevents the chip from operating at exceedingly high temperatures. when the silicon die temperature exceeds its upper threshold, it shuts down the whole chip. when the temperature drops below its lower threshold, the chip is enabled again.
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 12 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. design example tv led backlighting the design example introduces an MP4700- based high-performance tv led backlighting solution. figure 2 shows the structure of this total system solution?flyback+MP4700 low- side buck for single-string tv led backlight. the flyback converts the ac input line voltage to the system output supply voltage 13v/2a, and also outputs a dc bus voltage (around 280v) to the led driver. the flyback is based on the mps quasi-resonant flyback controller, hfc0100. the MP4700 acts as the led driver stage as a boundary conduction mode (bcm) low-side buck. figure 2: power system structure specifications: description parameter units input voltage 110 to 265 vac input frequency 50 hz output dc bus voltage 13.4 v output dc bus current 2 a led voltage 210 v led current 250 ma protection: short led protection, open led protection and 13v over-voltage protection. schematics: figure 3 and figure 4 show the schematics of the hfc0100 flyback stage and the MP4700 led driver stage. the parameters of the power transformer t2 are as follow: turn ratio: n p :n bus1 :n bus2 :n 13v :n au =45:51:51:5:10 primary inductance: l p =360 h. in this application example, the bus voltage uses 2 windings. each winding outputs half of the bus voltage (140v) after the rectifier, dividing the voltage stress across each rectifier diode. the reduced stress allows for the use of 800v diodes. both the 13v voltage and the 280v bus voltage feed back to the flyback control circuit, which decreases the influence of the cross regulation. the 13v system voltage also supplies the MP4700. the following describes the design of the MP4700 led driver. the design procedure for the hfc0100 flyback is not described here, but rather in the hfc0100 design materials.
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 13 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. pgnd pgnd pgnd 200/1206 r17 402k r35 5a/250v f1 12mh lx2 20k r26 5.11k r29 33pf c22 ns r20 fr107 d7 4.7nf/1kv c7 150k r7 150k r8 91k r27 c20 v40120c d9 470pf/100v c13 200/1206 r16 c19 l2 nc r39 23.7k/1% r25 300m/1% r33 ns r34 220pf c24 1.5nf/400v cy1 c21 8.2nf c23 5.1 ohms rt1 c15 33pf c25 51k r21 c16 c17 10 r24 v700c q3 2k r28 pc817a u2 bav21 d8 cn1 tvr10431 va1 cx1 cx2 1m r4 1m r12 1m r5 1m r13 12mh lx1 220pf/400v cy6 220pf/400v cy4 1nf/400v cy8 1nf/400v cy3 1nf/400v cy5 1nf/400v cy7 gnd 7 vcc 2 fb 8 drv 5 cs 6 demag 1 na 3 hv 4 u1 c14 c11 c12 1.5nf/400v cy2 5a/250v f2 d5 pg5406 d10 pg5406 d6 pg5406 d11 pg5406 her208 d2 10k r19 c18 c2 nc c3 c4 l1 1m/1% r10 374k/1% r15 6.81k/1% r30 q5 2n7002 8.2k/1% r38 10k r23 47k r31 68k r37 q4 q1 q6 10k r32 10k r40 c26 c27 d14 1n4148/sod-123 d13 1n4148/sod-123 510 r22 510 r36 30k/2w r3 10k r14 c8 510 r11 100nf/400v c5 agnd agnd agnd tl431k u3 on/off pwm ps_on 280v gnd ss8050 q2 13v d12 1k r18 nc d1 2k/1206 r2 2k/1206 r1 22pf/1000v c1 4 1 6 5 7 10 12 8 9 11 primary output feedback output output t1 12 9 6 3 11 8 10 5 7 2 4 1 cn2 13v her208 d3 nc d4 agnd 2k/1206 r9 22pf/1000v c6 2k/1206 r6 c10 nc c9 275v 1206 1206 1206 1206 275v 1000v/1a 1206 200v/0.2a 1206 1206 800v/2a 800v/2a 120v/40a adim figure 3: hfc0100 flyback schematic c28 led_n led_p std3nk60zt4 q7 10pf/630v c30 led_n l3 wegp30g/400v/3a d15 agnd option for open protection c32 r43 r41 20k r46 2k r45 1nf c31 1nf c29 agnd agnd 280v 1n4148w d16 2k r44 on/off pwm c33 agnd 13v r48 r49 2k r47 q8 fmmt558ta/sot23 300k r42 r51 30k r52 10k r54 agnd q10 10k r53 1nf c34 r41x -400v 1206 1206 0805 2k r55 adim inuv 1 pwm 2 gnd 3 vin 4 vcc 5 tst 6 orv 7 cs 8 u2 MP4700 figure 4: MP4700 low-side buck led driver schematic
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 14 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. select the inductor the MP4700 operates at bcm. select a proper inductor to ensure that the operating frequency is within a desired range. assuming the 280v bus voltage has -10% to +20% variation, and the led voltage has a 10% variation. the maximum system operating frequency at the maximum input bus voltage and the minimum output led voltage should not exceed the MP4700?s 160khz frequency limit. bus _ max led _ min led _ min s_max led bus_max (v v ) v 1 l f2i v ?? ?? ?? choosing a maximum operating frequency at 150khz, the inductor should exceed 1.1mh. the peak inductor current is around 2 times the led current when the MP4700 operates in bcm. an inductor rated at 1.3mh/0.6a would fit this application. select the power mosfet the voltage stress of the power mosfet should exceed the bus voltage. a mosfet with 400v voltage rating will suffice for this application. the peak current through the mosfet equals the peak inductor current, or 2 times the led current (250ma). the maximum rms current through the mosfet is: led _ max rms _ mos _ max led bus _ min v i 2i * 0.27a 3v ?? choose a mosfet with a current rating around 2a to 3a. select the diode the voltage stress of the diode should exceed the bus voltage?400v will suffice for this application. the maximum average current through the diode is: led _ min avg _ diode _ max led bus _ max v i2i*(1)0.21a v ?? ? this allows for a current rating within 1a to 2a. select the current sense resistor the MP4700 operates in bcm and the current sense resistor is: sense led 302mv r600m 2i ? ?? ? select the output capacitor the output capacitor should be large enough to filter the output ripple current and limit the led current ripple to within a desired range (usually below 5%). use the equivalent dynamic resistance of the led string to design the output capacitor. figure 5 defines of the equivalent dynamic resistance of the led string (r led ). i led v led led led led i v r ? ? ? figure 5: led equivalent dynamic resistance calculate the value of the ceramic output capacitor as: l _ peak out s _ min led led _ ripple _ pk _ pk i c 8f r i ? ?? where f s_min is the minimum operating frequency, which occurs at the minimum input voltage and maximum output voltage condition for this application.
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 15 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. bus _ min led _ max led _ max s_min l _ peak bus _ min (v v ) * v f l*i *v ? ? considering that i l_peak =2i led , the output capacitor value is: 2 led bus _ min out bus _ min led _ max led _ max led led _ ripple _ pk _ pk l*i *v c 2( v v ) * v r i ? ??? if using an electrolytic output capacitor, its esr dominates its impedance. the esr value should be: led led _ ripple _ pk _ pk esr _ cout l _ peak ri r i ? ? usually, a 1 f to 2.2 f ceramic capacitor or a 10 f to 22 f electrolytic capacitor should suffice for this led current level. select the input capacitor select the input capacitor to ensure that the input voltage ripple is within a desired range (1% to 5% of the input bus voltage). the input capacitor is usually electrolytic and its esr dominates its impedance. the esr of this input capacitor should be: bus _ ripple _ pk _ pk esr _ cin l _ peak v r i ? a 4.7 f to 22 f electrolytic capacitor will usually suffice. pcb layout guide for best results, follow these layout guidelines for the MP4700 low-side buck: (1) make the high-frequency switching loop (the input capacitor, the diode, the power mosfet and the current sense resistor) as small and tight as possible. (2) place the current sense resistor close to the ic and make the current sense loop as small as possible. (3) separate the gnd of MP4700 from the power ground of system, which conducts current of power stage. figure 6 and figure 7 show an example of the pcb layout. figure 7 shows the high-frequency switching loop (composed of the input capacitor, the diode, the power mosfet and the current sense resistor) marked in red. make sure to minimize this high-frequency switching loop.
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 16 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. figure 6: top layer figure 7: bottom layer
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 17 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. system performance led driver stage efficiency system efficiency analog dimming curve v sw 100v/div. v led+ 100v/div. v cs 500mv/div. i l 500ma/div. v sw 100v/div. v led+ 100v/div. v cs 200mv/div. i l 500ma/div. v pwm 2v/div. v led+ 100v/div. v led- 100v/div. i led 200ma/div. v cs 200mv/div. v sw 100v/div. v adim 2v/div. i led 200ma/div. steady state startup analog dimming bus voltage (v) input ac line voltage (v) pwm dimming duty(%) vadim (v) 96.4 96.6 96.8 97.0 97.2 97.4 97.6 97.8 98.0 98.2 98.4 250 260 270 280 290 300 86.5 87 87.5 88 88.5 89 100 140 180 220 260 280 0 50 100 150 200 250 300 0 20 40 60 80 100 0 50 100 150 200 250 300 0 20 40 60 80 100 0 50 100 150 200 250 300 0 0.5 1 1.5 2 2.5 3 3.5
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver MP4700 rev. 1.0 www.monolithicpower.com 18 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. v led+ 100v/div. 13v v led- 100v/div. i l 500ma/div. v pwm_ic 2v/div. v led+ 100v/div. v led- 100v/div. i led 200ma/div. v pwm_ic 2v/div. v led+ 100v/div. v led- 100v/div. i led 200ma/div.
MP4700 ? high-brightness bcm, low si de buck wled drive wled driver notice: the information in this document is subject to change wi thout notice. users should warrant and guarantee that third party intellectual property rights are not infringed upon when integrating mps products into any application. mps will not assume any legal responsibility for any said applications. MP4700 rev. 1.0 www.monolithicpower.com 19 10/29/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. package information soic8 0.016(0.41) 0.050(1.27) 0 o -8 o detail "a" 0.010(0.25) 0.020(0.50) x 45 o see detail "a" 0.0075(0.19) 0.0098(0.25) 0.150(3.80) 0.157(4.00) pin 1 id 0.050(1.27) bsc 0.013(0.33) 0.020(0.51) seating plane 0.004(0.10) 0.010(0.25) 0.189(4.80) 0.197(5.00) 0.053(1.35) 0.069(1.75) top view front view 0.228(5.80) 0.244(6.20) side view 14 85 recommended land pattern 0.213(5.40) 0.063(1.60) 0.050(1.27) 0.024(0.61) note: 1) control dimension is in inches. dimension in bracket is in millimeters. 2) package length does not include mold flash, protrusions or gate burrs. 3) package width does not include interlead flash or protrusions. 4) lead coplanarity (bottom of leads after forming) shall be 0.004" inches max. 5) drawing conforms to jedec ms-012, variation aa. 6) drawing is not to scale. 0.010(0.25) bsc gauge plane

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