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mp24971 1.5a, 50v, 100khz, 5v fixed output step- down converter with programmable current limit and output li ne-drop compensation mp24971 rev. 1.01 www.monolithicpower.com 1 1/6/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. the future of analog ic technology description the mp24971 is a monolithic, step-down, switch-mode converter with a programmable output-current limit. it has a fixed 5v/1.5a continuous output over a wide input supply range, and has excellent load and line regulation. it has an internal 2ms-to-4ms soft- start that prevents inrush current at start-up, and compensates for output line drop. mp24971 achieves a low emi signature with well-controlled switching edges. it has fault-condition protections including hiccup-mode current limit protection, short- circuit protection, output over-voltage protection, and thermal shutdown. the mp24971 requires a minimal number of readily-available standard external components, and is available in soic8 and soic8e packages. features ? wide 8v-to-50v operating input range ? output over-voltage protection ? 5v fixed output ? 0.4 ? internal power mosfet ? internal 4ms soft-start ? stable with low-esr ceramic output capacitors ? fixed 100khz frequency ? low emi signature ? thermal shutdown ? output line-drop compensation ? hiccup circuit limit and short circuit protection ? available in soic8 and soic8e package applications ? usb power supplies ? automotive power adapters ? power supplies for linear chargers a ll mps parts are lead-free and adhere to the rohs directive. for mps green status, please visit mps website under products, quality assurance page. ?mps? and ?the future of analog ic technology? are registered trademarks of monolithic power systems, inc. typical application + l 1 33h mp24971 sw voc isp isn vos bst vin gnd c 7 0.1f gnd v in r 2 402ko diode c 8 22f c 9 100f r sense 66mo c 10 0. 1 f r 3 1ko r 4 1ko c 5 10nf c 6 10nf r 5 0o r 1 0o c 4 0.1f c 3 0.1f c 1 220f c 2 2.2f v out efficiency vs. output current 55 60 65 70 75 80 85 90 95 output current (a) efficiency (%) 0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 v in =12v v in =24v v in =50v v out =5v
mp24971 ?1.5a, 50v, 100khz, 5v fixed output step-down converter mp24971 rev. 1.01 www.monolithicpower.com 2 1/6/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. ordering information part number package top marking operating temperature (t j ) mp24971ds * soic8 mp24971 -40 ? c to +125 ? c MP24971DN ** soic8e mp24971 -40 ? c to +125 ? c * for tape & reel, add suffix ?z (eg. mp24971ds?z); for rohs, compliant packaging, add suffix ?lf (eg. mp24971ds?lf?z). * * for tape & reel, add suffix ?z (eg. MP24971DN?z); for rohs, compliant packaging, add suffix ?lf (eg. MP24971DN?lf?z). package reference soic8 soic8e absolute maxi mum ratings (1) input voltage v in .......................................... 60v v isn, v isp, v vos ........................................ 0v to 8v |v isn - v isp | ........................................... 0v to 0.4v v sw ..................................... -0.3v to (v in + 0.3v) v bst ................................................... v sw + 6.5v all other pins ............................... -0.3v to +6.5v junction temperature ............................... 150c lead temperature .................................... 260c storage temperature ............... -65c to +150c continuous power dissipation (t a = 25c) (2) soic8 ...................................................... 1.38w soic8e ...................................................... 2.5w esd susceptibility hbm (human body mode).......................... 2kv recommended operating conditions (3) input voltage v in ................................. 8v to 50v maximum junction temp. (t j ) ................ 125c thermal resistance (4) ja jc soic8 ..................................... 90 ...... 45 ... c/w soic8e .................................. 50 ...... 10 ... 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 powe r 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.
mp24971 ?1.5a, 50v, 100khz, 5v fixed output step-down converter mp24971 rev. 1.01 www.monolithicpower.com 3 1/6/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. electrical characteristics v in = 12v, t a = 25c, unless otherwise noted. parameters symbol condition min typ max units output voltage v out 8v ? v in ? 50v, r sense =0 ? 4.85 5 5.15 v output over-voltage protection v ovp 5.69 6 6.2 v switch-on resistance r ds(on) 0.4 0.5 ? switch leakage v isn = 6.5v, v sw = 0v 0.1 1 (5) a current limit 3.5 4.4 5.2 a oscillator frequency f sw 70 100 140 khz bootstrap voltage v bst - v sw 4 v minimum on time t on 50 100 250 ns sw rising edge t rise 50 100 ns sw falling edge t fall 85 150 ns under-voltage lockout threshold rising 2.8 3.5 4.2 v under-voltage lockout threshold hysteresis 200 mv load-line compensation gain v voc v isp -v isn =50mv 200 330 450 mv v isp -v isn =100mv 500 620 700 current sense voltage v isp -v isn v isn =5v 90 100 110 mv input bias current (isn, isp) i bias ( isn , isp ) v isp =v isn =5v -1 -0.5 +1 a supply current (quiescent) v isn = v vos = 5.5v 1.2 1.5 ma thermal shutdown 150 c note: 5) guaranteed by design.
mp24971 ?1.5a, 50v, 100khz, 5v fixed output step-down converter mp24971 rev. 1.01 www.monolithicpower.com 4 1/6/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. pin functions package pin # name description 1 vin supply voltage. operates from an unregulated 8v-to-50v input. requires decoupling capacitor(s)?c in ?to limit voltage spikes. drain of the internal power mosfet; supplies power to the whole chip. 2 gnd exposed pad ground. voltage reference of the regulat ed output voltage. gnd node should be placed outside of the diode-to-c in ground path to prevent switching current spikes from inducing voltage noise into the part. connect exposed pad to gnd plane for optimal thermal performance. 3 vos output voltage sense. connect directly to the output. 4 voc output line drop compensator. connect to gnd through a resistor to compensate for the output voltage drop. 5 isn negative current sense input. used for limiting load current and for over-voltage protection. native 6v over-voltage protection threshold. 6 isp positive current sense input. used for load current limiting. 7 bst bootstrap. requires a capacitor to driv e the power mosfet gate above the supply voltage. connected capacitor between sw and bst pins to form a floating supply across the power mosfet driver. an on-chip regulator charges the external bootstrap capacitor. if the on-chip regulator is not powerful enough, add a diode from v in or v out to charge the external boot-strap capacitor. 8 sw switch output. output power supply.
mp24971 ?1.5a, 50v, 100khz, 5v fixed output step-down converter mp24971 rev. 1.01 www.monolithicpower.com 5 1/6/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical characteristics current limit vs. temperature v vos vs. temperature v ovp vs. temperature v voc vs. temperature v isp -v isn =100mv frequency vs. temperature quiescent current vs. temperature v isp -v isn vs. temperature v isn=5v v bst vs. temperature i bias(isp,isn) vs. temperature v isp =v isn =5v -0.85 -0.8 -0.75 -0.7 -0.65 -0.6 -0.55 -0.5 -0.45 -50 -20 10 40 70 100 130 4.4 4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 5.3 5.4 -50 -20 10 40 70 100 130 current limit(a) 4.94 4.9425 4.945 4.9475 4.95 4.9525 4.955 4.9575 4.96 -50 -20 10 40 70 100 130 v vos (v) 100 101 102 103 104 105 106 107 108 109 110 -50 -20 10 40 70 100 130 frequency(khz) 5.9 5.91 5.92 5.93 5.94 5.95 5.96 -50 -20 10 40 70 100 130 v ovp (v) 615 620 625 630 635 640 -50 -20 10 40 70 100 130 v voc (mv) 3.8 3.85 3.9 3.95 4 4.05 4.1 -50 -20 10 40 70 100 130 v bst (v) 1130 1140 1150 1160 1170 1180 1190 1200 1210 1220 -50 -20 10 40 70 100 130 100 100.5 101 101.5 102 102.5 103 103.5 104 104.5 105 -50 -20 10 40 70 100 130 v isp -v isn (mv)
mp24971 ?1.5a, 50v, 100khz, 5v fixed output step-down converter mp24971 rev. 1.01 www.monolithicpower.com 6 1/6/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical performanc e characteristics c1=220 f, c2=2.2 f, c8=22 f, c9=100 f, l=33 h, r sense =66m ? , t a =25c, unless otherwise noted. output line drop compensation connect isp, isn to gnd i out (a) i out (a) v out (v) loop gain with phase margin 0.1 1 10 100 1000 frequency(khz) -200 -160 -120 -80 -40 0 40 80 120 160 200 gain (db) phase (degree) efficiency vs. output current 55 60 65 70 75 80 85 90 95 i out (a) load regulation v out (v) v out =5v 4.9 4.91 4.92 4.93 4.94 4.95 4.96 0 0.2 0.4 0.6 0.8 1 1.2 1.4 v in =12v v in =24v v in =50v 0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 v in =12v v in =24v v in =50v 4.93 4.935 4.94 4.945 4.95 4.955 4.96 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 30 100 1000 v in =12v v in =24v v in =50v v in =12v, v out =5v, i out =1.5a frequency(mhz) emi radiation -50 -40 -30 -20 -10 0 10 20 30 40 50 -10 0 10 20 30 40 50 60 70 80 90 resistor load en55022 v in =12v, v out =5v, i out =1.5a resistor load
mp24971 ?1.5a, 50v, 100khz, 5v fixed output step-down converter mp24971 rev. 1.01 www.monolithicpower.com 7 1/6/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical performanc e characteristics (continued) c1=220 f, c2=2.2 f, c8=22 f, c9=100 f, l=33 h, r sense =66m ? , t a =25c unless otherwise noted. sw 10v/div v in /ac 500mv/div v out /ac 20mv/div i l 2a/div sw 10v/div v out 5v/div i l 2a/div sw 10v/div v out 500mv/div i out 2a/div sw 10v/div v out 5v/div i out 2a/div v out 200mv/div i out 1a/div steady state v in =12v, v out =5v, i out =1.5a e-load steady state v in =50v, v out =5v, i out =1.5a e-load power ramp up v in =12v, v out =5v, i out =1.5a resistor load power ramp down v in =12v, v out =5v, i out =1.5a resistor load short circuit enter v in =12v, v out =5v, i out =0.5a short circuit recovery v in =12v, v out =5v, i out =0.5a load transient response v in =12v, v out =5v, i out =0.3a-1.5a slew rate=6.4ma/s over voltage protection v in =12v, v out =5v, i out =1.5a add an 6v external power to isn short circuit steady v in =12v, v out =5v sw 50v/div v in /ac 1v/div v out /ac 50mv/div i l 2a/div v in 10v/div sw 10v/div v out 5v/div i out 2a/div v in 10v/div sw 10v/div v out 5v/div i out 2a/div v isn 5v/div i out 2a/div sw 10v/div v out 5v/div
mp24971 ?1.5a, 50v, 100khz, 5v fixed output step-down converter mp24971 rev. 1.01 www.monolithicpower.com 8 1/6/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. functional block diagram regu lat or reference 63mo current sense amplifier regulator driver oscillator ramp s q r pwm comparator c 1 1pf r 1 1704ko c 2 50pf clk error amplifier vin vos bst sw isp isn hiccup current limit gnd 600mv 10000ko 10pf 200mv in x6 r s1 r s2 800mv ss circuit 6.2ua ovp comparator 1.23v voc r top 300ko r bot 57.14ko r c r sense nmosfet jfet jfet out figure 1?function block diagram
mp24971 ?1.5a, 50v, 100khz, 5v fixed output step-down converter mp24971 rev. 1.01 www.monolithicpower.com 9 1/6/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. operation main control loop the mp24971 is a current-mode buck regulator where the output voltage of the error amplifier (ea) is proportional to the peak inductor current. when a cycle starts, sw is disconnected and the ea output voltage is higher than the current sense amplifier (csa) output. the rising edge of the 100khz clk signal sets the rs flip-flop, which connects sw and the inductor to the input supply. the csa amplifies the rising inductor current. the pwm comparator (pwm comp ) compares sum of the csa output and the ramp compensation (positive input) against the ea output (negative input). when the positive pwm comp input exceeds the negative pwm comp input, the rs flip-flop resets and the mp24971 reverts to its initial sw off state: otherwise, the falling edge of the clk resets the flip-flop. the ea amplifies the voltage difference between v out (connected through the vos pin) and the 800mv reference: because v out connects to the negative input of the ea, when v out drops below 5v, the ea output increases. since the ea output voltage is proportional to the peak inductor current, an increase in inductor voltage increases current delivered to the output. an external schottky diode dissipates the inductor current when sw is off. hiccup-mode current limit protection the isp and isn pins sense the output current information for current limit protection. once the v sense exceeds the 100mv voltage limit threshold, the current limit loop will turn off the high-side mosfet immediately. the internal soft-start circuit resets after the vos voltage drops below 1.9v and v comp rises above 3v; at this point, the high side switch turns on and mp24971 restarts with a full soft start. this hiccup process repeats until the device stops detecting a fault. the current limit value can be lowered by an internal current source and external resistors connected to isn and isp pins when the output voltage drops below 200mv. this feature can greatly reduce the average short circuit current. output over-voltage protection the mp24971 has output over-voltage protection to prevent the output voltage from rising above a threshold of 6v?such as if the output sense is left open?and prevents any voltage damage to the circuit load. if the output voltage?as sensed by the isn pin?rises above 6v, the high-side mosfet will turn off immediately and part will be lathed off after a timer delay. output-line?drop compensation mp24971 is capable of compensating an output voltage drop?such as high impedance caused by a very long trace?to keep a constant 5v load-side voltage. compensation feedback comes from the vos pin and through the r top resistor. program the load line compensation gain using a resistor connected to voc pin, selected based on r sense and r trace (figure 2) values.
mp24971 ?1.5a, 50v, 100khz, 5v fixed output step-down converter mp24971 rev. 1.01 www.monolithicpower.com 10 1/6/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. application information setting the output line drop compensation long traces to the circuit load induce a voltage drop between v out and v load . that can be described as: drop out trace vir ?? (1) where trace trace1 trace2 rr r ?? as seen in figure 2. then, the v load is: load out out trace vvir ??? (2) supplying an accurate and consistent load voltage over current-dependant trace resistance necessitates line-drop compeonsation. mp24971 offers a compensation method that adjusts the fb voltage slightly according to the load current. the relation between v out and v fb can be described by: out fb out sense fb top bot c vv ir 6 v rr r ??? ?? (3) where, v fb is 0.8v. then, the v out can be calculated by: out sense top out c ir 6r v5v r ??? ?? (4) the v load is determined by: out sense top load c out trace ir 6r v5v r ir ??? ?? ?? (5) to maintain a v load that is not variable with load current, balance the equation below: out sense top out trace c ir 6r ir r ??? ?? (6) where r top is 300k ? . simplifying, we find that r c comes out to: sense c trace r6300k r r ?? ? ? (7) where r sense is known and r trace can be tested or evaluated sw isp isn r sense 0.8v vos load v out error amplifier r top r bot 600mv x 6 hiccup current limit 10000ko 10pf internal block r trace r trace1 r trace2 voc r c v fb v load figure 2?output line drop compensation selecting the inductor for most applications, use a 10h to 47h inductor with a dc current rating of at least 125% of the maximum load current. for best efficiency, select an inductor with a dc resistance less than 200m ? . for most designs, the inductance value can be determined by. osc l in out in out f i v ) v v ( v l ? ? ? ? ? ? (8) where i l is the inductor ripple current. choose inductor current ripple to equal approximately 30% of the maximum load current, 1.5a. then maximum inductor peak current is: 2 i i i l load ) max ( l ? ? ? (9) under light-load conditions below 100ma, use a larger inductor to improve efficiency.
mp24971 ?1.5a, 50v, 100khz, 5v fixed output step-down converter mp24971 rev. 1.01 www.monolithicpower.com 11 1/6/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. selecting the input capacitor an input capacitor reduces the surge current drawn from the input and any switching noise from the device. chose a capacitor with a switching-frequency impedance less than the input source impedance. use ceramic capacitors with x5r or x7r dielectrics for their low esr and small temperature coefficients. a capacitor value of 4.7f will suffice for most applications. selecting the output capacitor an output capacitor limits the output voltage and ensures regulator loop stability. chose an output capacitor with a low impedance at the switching frequency; preferably ceramic with x5r or x7r dielectrics. setting the current limit the inductor?s dc resistance (dcr) sets the hiccup current limit. use a sense resistor with high precision and accuracy for accurate sense measurement. in figure 3a, the output current limit is: out _ l 100mv i dcr ? (10) where r a and c a form a low pass filter. in figure 3b, the output current limit is set as: out _ l sense 100mv i r ? (11) programming the short circuit current limit the hiccup current limit at output short condition can be programmed to be lower by external resisters (r s1 , r s2 , r s1 =r s2 ), as shown in figure 4. when output voltage is lower than 200mv, the current limit is described by: out _ sl sense s1 i r 6.2 a r 100mv ????? (12) the current limit at output short condition is: s1 out _ sl sense 100mv 6.2 a r i r ??? ? (13) sw isp isn r a r s2 r s1 sw isp isn r sense r s2 r s1 (a) (b) c a figure 3?current sensing methods sw isp isn r sense r s1 r s2 200mv 6.2ua figure 4?short circuit current limit
mp24971 ?1.5a, 50v, 100khz, 5v fixed output step-down converter mp24971 rev. 1.01 www.monolithicpower.com 12 1/6/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. pc board layout the high frequency paths for vin, sw and gnd should be routed very close to the device with short, direct, and wide traces. place the input capacitor as close as possible to the in and gnd pins. place the external feedback resistors next to the fb pin. keep the switching node sw short and away from the feedback network. external bootstrap diode an external bootstrap diode helps improve the efficiency of the regulator when the system has a 5v fixed input or the power supply generates a 5v output. the bootstrap diode can be low- cost, such as an in4148 or a bat54. add a diode for high duty-cycle operation (when out in v v >65%). mp24971 bs sw 10nf 5v figure 5?external bootstrap diode design example below is a sample design that follows the application guidelines for the specifications below: parameter symbol value units input voltage v in 8 - 50 v output voltage v out 5 v output current limit i out-l 1.5 a output ovp v ovp 6 v figure 6 shows the detailed application schematic. the typical performance characteristics performance and circuit waveforms are all based on this design. for additional implentations, consult the evaluation board data sheets. + l1 33h mp24971 sw voc isp isn vos bst vin gnd gnd c 7 0.1f gnd v in vcc d 1 ns r 2 402ko d 2 b360a c 8 22f c 9 100f r 6 100mo c 10 ns c 11 0.1f r 3 1ko r 4 1ko c 5 10nf c 6 10nf r 8 0o r 1 0o c 4 0.1f c 3 0.1f c 1 100f c 2 2.2f v out r 5 100o r 7 165o figure 6?detailed sample application schematic
mp24971 ?1.5a, 50v, 100khz, 5v fixed output step-down converter mp24971 rev. 1.01 www.monolithicpower.com 13 1/6/2012 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
mp24971 ?1.5a, 50v, 100khz, 5v fixed output step-down converter notice: the information in this document is subject to change wi thout notice. please contact m ps for current specifications. users should warrant and guarantee that third party intellectual property rights ar e not infringed upon when integrating mps products into any application. mps will not assume any legal responsibility for any said applications. mp24971 rev. 1.01 www.monolithicpower.com 14 1/6/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. package information soic8e (exposed pad) see detail "a" 0.0075(0.19) 0.0098(0.25) 0.050(1.27) bsc 0.013(0.33) 0.020(0.51) seating plane 0.000(0.00) 0.006(0.15) 0.051(1.30) 0.067(1.70) top view front view side view bottom view 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 ba. 6) drawing is not to scale. 0.089(2.26) 0.101(2.56) 0.124(3.15) 0.136(3.45) recommended land pattern 0.213(5.40) 0.063(1.60) 0.050(1.27) 0.024(0.61) 0.103(2.62) 0.138(3.51) 0.150(3.80) 0.157(4.00) pin 1 id 0.189(4.80) 0.197(5.00) 0.228(5.80) 0.244(6.20) 14 85 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 0.010(0.25) bsc gauge plane

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