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mp24943 3a, 55v, 100khz step -down converter with programmable output ovp threshold mp24943 rev. 1.0 www.monolithicpower.com 1 9/13/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. the future of analog ic technology description the mp24943 is a monolithic, step-down, switch-mode converter. it supplies 3a of continuous output current over a wide input- supply range with excellent load and line regulation. mp24943 achieves low emi signature with well- controlled switching edges. fault condition protection includes programmable-output over-voltage protection, cycle-by-cycle current limit, and thermal shutdown. mp24943 requires a minimal number of readily- available standard external components. it is available in soic8 and soic8e package. features ? wide 4.5v to 55v operating input range ? programmable output over-voltage protection ? output adjustable from 0.8v to 45v ? 0.15 ? internal power mosfet switch ? stable with low esr output ceramic capacitors ? fixed 100khz frequency ? low emi signature ? thermal shutdown ? cycle-by-cycle over-current protection ? available in soic8 and soic8e packages applications ? automotive gps ? automotive entertainment ? power supply for linear chargers for mps green status, please visit mps website under quality assurance. ?mps? and ?the future of analog ic technology? are registered trademarks o f monolithic power systems, inc. typical application 50 55 60 65 70 75 80 85 90 95 0 0.5 1 1.5 2 2.5 3 v in =12v v in =24v v in =55v
mp24943 ?3a, 55v, 100khz step-down converter mp24943 rev. 1.0 www.monolithicpower.com 2 9/13/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. ordering information part number package top marking free air temperature (t a ) MP24943DS * soic8 mp24943 -40c to +85c mp24943dn ** soic8e mp24943 -40c to +85c * for tape & reel, add suffix ?z (eg. MP24943DS?z); for rohs, compliant packaging, add suffix ?lf (eg. MP24943DS?lf?z). * for tape & reel, add suffix ?z (eg. mp24943dn?z); for rohs, compliant packaging, add suffix ?lf (eg. mp24943dn?lf?z). package reference vin gnd en fb sw bst vo ss 1 2 3 4 8 7 6 5 top view vin gnd en fb sw bst vo ss 1 2 3 4 8 7 6 5 top view exposed pad on backside connect to pin 2 soic8 sioc8e absolute maxi mum ratings (1) input voltage v in .......................................... 60v 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 recommended operating conditions (3) input voltage v in .............................. 4.5v to 55v output voltage v out ......................... 0.8v to 45v 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.
mp24943 ?3a, 55v, 100khz step-down converter mp24943 rev. 1.0 www.monolithicpower.com 3 9/13/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. electrical characteristics v in = 12v, t a = 25c, unless otherwise noted. parameters symbol condition min typ max units feedback voltage v fb 4.5v ? v in ? 55v 0.78 0.80 0.82 v feedback bias current i bias(fb) v fb = 0.8v -100 10 100 na output over-voltage reference v ovref 0.88 0.92 0.96 v switch-on resistance r ds(on) 0.125 0.15 ? switch leakage v en = 0v, v sw = 0v 0.1 1 a current limit duty cycle=10% 5.5 6.5 8 a oscillator frequency f sw v fb = 0.6v 70 100 140 khz bootstrap voltage v bst - v sw 4.3 5.5 v minimum-on time t on 50 100 250 ns sw-rising edge t rise 50 100 ns sw-falling edge t fal l 50 100 ns en-input low voltage 0.4 v en-input high voltage 1.8 v en-input bias current v en =0-6v -10 -2 10 a under-voltage lockout threshold rising 3.0 3.3 3.6 v under-voltage lockout threshold hysteresis 200 mv supply current (shutdown) v en =0v 4 10 a supply current (quiescent) v en = 2v, v fb = 1v 650 800 a thermal shutdown 150 c
mp24943 ?3a, 55v, 100khz step-down converter mp24943 rev. 1.0 www.monolithicpower.com 4 9/13/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. pin functions package pin # name description 1 vin supply voltage. unregulated input can ran ge from 4.5v to 55v. input capacitor (c in ) required to decouple input. provides drain for internal power device and power supply. 2 gnd, exposed pad ground. voltage reference for the regulat ed output voltage. layout requires special attention: this node must be pl aced outside of the d1-to-c in ground path to prevent current spikes from inducing voltage noise. connect exposed pad to gnd plane for optimal thermal performance. 3 en enable input. pull this pin below the specified threshold to shut the chip down. pull it above the specified threshold enables the chip. 4 fb feedback. use an external resistor divider from v out to gnd tapped to the fb pin to set the output voltage. 5 ss soft-start. connect to an exte rnal capacitor for soft-start. 6 vo output over-voltage protection. connect vo to the tap of an external resistor divider from v out to gnd. the ovp reference is 0.9v. 7 bst bootstrap. requires a capacitor to drive the power switch?s gate above the supply voltage. connect this capacitor between sw and bst pins to form a floating supply across the power switch driver. an on- chip regulator charges up the bootstrap capacitor. if the on-chip regulator is not strong enough, one optional diode can be connected from v in or v out to charge the external boot-strap capacitor. 8 sw switch output. output supply.
mp24943 ?3a, 55v, 100khz step-down converter mp24943 rev. 1.0 www.monolithicpower.com 5 9/13/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. typical characteristics v in =12v current limit vs. temperature frequency vs. temperature v bst vs. temperature quiescent current vs. temperature v ovref vs. temperature v fb vs. temperature 0.8025 0.803 0.8035 0.804 0.8045 0.805 -50 -20 10 40 70 100 130 -50 -20 10 40 70 100 130 -50 -20 10 40 70 100 130 -50 -20 10 40 70 100 130 o c) v fb (v) v ovref (v) v bst (v) 5 5.5 6 6.5 7 7.5 8 -50 -20 10 40 70 100 130 o c) -50 -20 10 40 70 100 130 98 100 102 104 106 108 110 0.91 0.915 0.92 0.925 0.93 0.935 0.94 4.4 4.425 4.45 4.475 4.5 4.525 4.55 4.575 4.6 550 560 570 580 590 600 610 620 630 640 650
mp24943 ?3a, 55v, 100khz step-down converter mp24943 rev. 1.0 www.monolithicpower.com 6 9/13/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. typical performanc e characteristics c1=220 f, c2=2.2 f, c3=100 f, c4=22 f, l=33 h, t a =25c unless otherwise noted. i out (a) i out (a) v out (v) frequency (khz) -80 -60 -40 -20 0 20 40 60 80 0.1 1 10 100 1000 -200 -150 -100 -50 0 50 100 150 200 50 55 60 65 70 75 80 85 90 95 0 0.5 1 1.5 2 2.5 3 4.97 4.975 4.98 4.985 4.99 4.995 5 5.005 5.01 0 0.5 1 1.5 2 2.5 3 v in =12v v in =24v v in =55v v in =55v v in =24v v in =12v en55022 v in /ac 500mv/div. v out /ac 50mv/div. v sw 10v/div. i l 2a/div. v in /ac 500mv/div. v out /ac 50mv/div. v sw 50v/div. i l 2a/div. v in 10v/div. v sw 10v/div. v out 5v/div. i l 2a/div. v in 10v/div. v sw 10v/div. v out 5v/div. v out 5v/div. i l 2a/div. v en 5v/div. v sw 10v/div. i out 5a/div.
mp24943 ?3a, 55v, 100khz step-down converter mp24943 rev. 1.0 www.monolithicpower.com 7 9/13/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. typical performanc e characteristics (continued) c1=220 f, c2=2.2 f, c3=100 f, c4=22 f, l=33 h, t a =25c unless otherwise noted. v out 5v/div. v en 5v/div. v sw 10v/div. i out 5a/div. v sw 10v/div. v out 5v/div. i out 5a/div. v sw 10v/div. v out 1v/div. i out 5a/div. v sw 10v/div. v out 5v/div. i out 5a/div. v out /ac 200mv/div. i out 2a/div. vo 1v/div. v out 5v/div. v sw 10v/div. i out 5a/div. vo 1v/div. v sw 10v/div. v out 5v/div. i out 5a/div.
mp24943 ?3a, 55v, 100khz step-down converter mp24943 rev. 1.0 www.monolithicpower.com 8 9/13/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. operation main control loop the mp24943 is a current-mode buck regulator where the error amplifier (ea) output voltage is proportional to the peak inductor current. at the beginning of the cycle, sw is off, the ea output voltage is higher than the current sense amplifier (csa) output, and output of the current limit comparator is low. the rising edge of the 100khz clk signal sets the rs flip-flop: this turns on the internal switch, which then connects sw and the inductor to the input supply. the csa detects the current flow through the internal switch. if the sum of the csa output and the slope compensation output exceeds the ea output voltage, the rs flip-flop resets, and the mp24943 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 fb and the 0.8v reference. when v fb is less than the 0.8v reference, the ea output is proportional to the inductor current. an external schottky diode (d1) carries the inductor current when sw is off. enable control the mp24943 has an enable-control pin (en): driving en above 1.8v turns on mp24943, while driving en below 0.4v turns it off. connect en to v in for automatic start-up. output over-voltage protection the mp24943 has output over-voltage protection (ovp), where v out connects to vo through an external resistor divider, and a 0.9v reference on the negative input of the ovp comparator. if the voltage on vo pin is greater than 0.9v, the high-side switch turns off after a short delay, and the soft-start capacitor discharges. if the voltage is less than 0.9v, the part restarts automatically.
mp24943 ?3a, 55v, 100khz step-down converter mp24943 rev. 1.0 www.monolithicpower.com 9 9/13/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. functional block diagram figure 1?functional block diagram
mp24943 ?3a, 55v, 100khz step-down converter mp24943 rev. 1.0 www.monolithicpower.com 10 9/13/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. application information setting the output voltage the external resistor divider?r1 and r2?sets v out (see the typical application circuit on the front page). r1 also sets the feedback loop bandwidth with the internal compensation capacitors (see figure 1). choose r1 to be around 300k ? for optimal transient response. choose r2 as determined by: 1 v 8 . 0 v 1 r 2 r out ? ? table 1?resistor selection for common output voltages v out (v) r1 (k ? ) r2 (k ? ) 1.8 301 (1%) 240 (1%) 2.5 301 (1%) 140 (1%) 3.3 301 (1%) 95.3 (1%) 5 301 (1%) 57.6 (1%) setting the output ovp threshold an external resistor divider?r5 and r6 (see the typical application circuit on the front page)?connected to vo sets the output ovp threshold. choose r5 to be 301k ? for reduced power dissipation. then r6 is given by: ovp ovref r5 r6 (k ) v 1 v ?? ? where, v ovref is the ovp reference, 0.9v, and v ovp is over voltage protection threshold. selecting the inductor include an inductor with a value between 22h and 47h and a dc current rating that is at least 25% percent higher than the maximum load current for most applications. for maximum efficiency, the inductor dc resistance should be less than 200m ? . for most designs, the inductance value can be estimated from the following equation. osc l in out in out f i v ) v v ( v l ? ? ? ? ? ? where i l is the inductor ripple current. choose the inductor current ripple to be approximately 30% of the maximum load current, 3a. the maximum inductor peak current is: 2 i i i l load ) max ( l ? ? ? under light-load conditions of <100ma, larger inductance values improve efficiency. selecting the input capacitor the input capacitor reduces the surge current drawn from the input and also the switching noise from the device. choose a capacitor with a switching-frequency impedance of less than the input source impedance to prevent any high-frequency switching current from flowing to the input. use ceramic capacitors with x5r or x7r dielectrics for their low esr and small temperature coefficients. use a 4.7f capacitor for most applications. selecting the output capacitor the output capacitor keeps the output voltage ripple small and ensures regulator loop stability. select an output capacitor with a low switching- frequency impedance, preferably ceramic capacitors with x5r or x7r dielectrics. pc board layout the high frequency path?gnd, in, and sw? should be placed 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 sw node short and away from the feedback network. external bootstrap diode add an external bootstrap diode when the system has a fixed 5v input or when the power supply generates a 5v output. this helps improve the efficiency of the regulator. the bootstrap diode can be a low-cost one such as in4148 or bat54.
mp24943 ?3a, 55v, 100khz step-down converter mp24943 rev. 1.0 www.monolithicpower.com 11 9/13/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. this diode is also recommended for high-duty? cycle operation (when out in v v >65%) and high output voltage (v out >12v) applications. figure 2?external bootstrap diode example design below is an example design that follows the application guidelines for the specifications: v in 8 to 55v v out 5v f sw 100khz v ovp 6v figure 3 shows the detailed application schematic. for more possible applications of this device, please refer to related evaluation board data sheets. + l1 33 h mp24943 sw vo fb gnd bst vin ss gnd c 6 0.1 f gnd v in vcc d 1 ns d 2 b560c c 5 22 f c 8 100 f r 5 0 r 1 0 c 1 0.1 f c 7 100 f c 2 2.2 f v out en c 9 0.1 f r 4 301k c 4 150pf r 8 57.6k en c 3 0.1 f r 6 680k r 7 42.2k r 2 237k r 3 ns u 1 figure 3?detailed application schematic
mp24943 ?3a, 55v, 100khz step-down converter mp24943 rev. 1.0 www.monolithicpower.com 12 9/13/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. package information soic8e (exposed pad)
mp24943 ?3a, 55v, 100khz 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. mp24943 rev. 1.0 www.monolithicpower.com 13 9/13/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. package information soic8

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