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mpm3684 18v 15a step - down power module in 12x15x4mm qfn mpm3684 rev. 1.0 2 www.monolithicpower.com 1 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. description the mpm3684 is a n easy - to - use fully integrated 15 a step - down dc/dc power module. it integrates the dc/dc converter, power inductor, input/output capacitors and the necessary resistors/capacitors in a compact qfn 1 2 mmx1 5 mmx4mm package. this tota l power solution needs as few as two external components (one resistor and one capacitor) to work. mpm3684 can deliver 15a output current over a wide input supply voltage range with excellent load and line regulation. the mpm3684 uses constant - on - time (co t) control to provide fast transient response and ease the loop stabilization. the default under voltage lockout threshold is internally set around 4.1v, but a resistor network on the enable pin can increase this threshold. the mpm3684 has an internal ldo to power the control circuits and the integrated power devices. this ldo can be disabled by an external 5v to boost the efficiency. the mpm3684 has an internal about 3ms soft start (ss) timer. it can be increased with an extra ss capacitor. an open drain power good signal indicates that the output voltage is within nominal voltage range. the mpm3684 has fully integrated protection features that include over - current protection, over - voltage protection and thermal shutdown. features ? complete 15a dc - to - dc s olution ? wide input voltage range from 2.5v: -- 2.5v to 18 v with external 5v bias -- 4.5v to 18v with internal bias ? 1% reference voltage over 0 ?c to 70?c junction temperature range ? adaptive cot control for u ltrafast transient response ? programmable switching frequency from 200 k hz to 1mhz ? support pre - bias start up ? programmable soft - start time with default 3ms ? non - latch ocp, ovp and thermal shutdown ? output adjustable from 0.65v to 5v ? qfn - 65 (12mm x 15mm x 4mm) p ackage applications ? telecom and networking systems ? base stations ? servers ? personal video recorders ? flat panel television and monitors ? distributed power systems all mps parts are lead - free , halogen - free, and adhere to the rohs directive. for mps green status, please visit the mps website under quality assuranc e . mps and the future of analog ic technology are r egistered t rademarks of monolithic power systems, inc.
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 2 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. typical application p g o o d c t r i m v o u t d c t r i m e n v i n i n e n p g a g n d g n d g n d v o u t g n d r t r i m a c t r i m f r e q > > f r e q m p m 3 6 8 4
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 3 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. ordering information part number* package top marking mpm368 4 gru qfn - 65 (12 mm x 15 mm x 4mm) see below top marking mps: mps prefix: yy: year code; ww: week code: mp3684: product code of mp m3684gru ; m: module lll llllll : lot number; package reference top view v i n a c _ t r i m p g v c c a g n d n / c s w s w g n d g n d g n d s s g n d v i n v i n g n d g n d g n d g n d g n d g n d g n d n / c v o u t v o u t s w s w s w s w s w s w s w a g n d a g n d a g n d e n > f e r q v i n d c _ t r i m > s w s w s w n / c v o u t v o u t v o u t v o u t v o u t v o u t s w f r e q > s w g n d v i n s w > d c _ t r i m v o u t s w a g n d n / c s w n / c b s t s w n / c 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 3 0 3 1 3 2 3 3 3 4 3 5 3 6 3 7 3 8 3 9 4 0 4 1 4 2 4 3 4 4 4 5 4 6 4 7 4 8 4 9 5 0 5 1 5 2 5 3 5 4 5 5 5 6 5 7 5 8 5 9 6 0 6 1 6 2 6 3 6 4 6 5
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 4 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. absolute maximum rat ings (1) supply voltage v in to gnd ............. - 0.3v to 21v v sw(dc) to gnd .......................... C 1v to v in +0.3v v sw5 (30ns) to gnd ............. C 3 v to v in +3v or 24v v bst ................................ ......... C 0.3 v to v in +6v all o ther pins to agnd ................. C 0.3v to +6v continuous output current ......................... 17 a junction temperature .............................. 150 ? c lead temperature ................................ ... 260 ? c storage temperature .............. C 55 ? c to +150 ? c msl ................................ ................... level 3 (5) esd (hbm) ................................ ................. 2kv esd (cdm) ................................ ............... 500v recommended operating conditions ( 3 ) supply voltage v in .......................... 4. 5v to 18 v output voltage v out ........................ 0. 65 v to 5 v enable current i en ......1ma ambient temperature ................ - 40 c to +85 c operating junction temp . (t j ). . - 40 c to +125 c thermal resistance ( 4 ) j b ja qfn - 65( 12 mm x15 mm x4 mm) .......................... 2.514.0 ? 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), t he junction - to - ambient thermal resistanc e 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. 3) the device is not guaranteed to function outside of its operating conditions. 4) measured on jesd51 - 7, 4 - layer pcb. 5) need to get some test data from 1 st sample for calibration and evaluation for msl level 2.
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 5 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. electrical character istics v in = 12v, v out = 1.2v, r trim = 10 k , c trim = 560pf, t j = 2 5 ? parameters symbol condition min typ max units input voltage range input voltage range v in 5v external vcc 2.5 18 v 4.5 18 v output voltage output voltage range 6) v out_range 0.65 5 v output v oltage accuracy (load regulation) 6) v out_dc_load c out =5x47 f ceramic, i out =0a to 15a 0.5 %vout output voltage accuracy (line regulation) 6) v out_dc_line c out =5x47 f ceramic, v in =4.5v to 18v, i out =5a 0.4 %vout quiescent current quiescent current i in v en = 2 v, v fb =0.65v 700 860 1000 ua current limit output current limit i lim 15 20 25 a switching frequency 6) switching frequency f sw i out =5a 400 500 600 k hz over - voltage and under - voltage protection ovp non - latch threshold 7) v ovp _non - la tch with negative current limit 117% 120% 123% v fb ovp threshold 6) v ovp_th no negative current limit 127% 130% 133% v fb uvp threshold 6) v uvp 47% 50% 53% v fb reference and soft start reference voltage 8) v ref t j = 0 ? c to +70 ? c 608 611 614 mv t j = 0 ? c to +120 ? c 605 611 617 mv t j = - 4 0 ? c to +125 ? c 602 611 620 mv soft start time t ss 2 2.8 3.6 ms timer 6) minimum on time t on_min 20 30 40 ns minimum off time t off_min 200 360 420 ns
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 6 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. electrical character istics (continued) v in = 12v, v out = 1.2v, r trim = 10k , c trim = 560pf, t j = 2 5 ? parameters symbol condition min typ max units power good power good rising threshold 7) pg vth - hi 87% 91% 94% v fb power good falling threshold 7) pg vth - lo 80% v fb power good low to high delay 7) pg td 2.5 ms power good sink current capability 7) i ol v ol =600mv 12 ma power good leakage current 7) i pg_leak v pg =3.3v 0.01 ua pg low - level output voltage v ol_100 v in =0v, pull pgood up to 3.3v through a 100k resistor. 500 550 600 mv v ol_10 v in =0 v, pull pgood up to 3.3v through a 10k resistor. 600 650 700 mv enable 7) e nable input low voltage vil en 1.1 1. 3 1.5 v e nable hysteresis v en - hys 2 5 0 mv e nable input current i en v en = 2v 0 a vcc regulator 7) vcc under voltage lockout threshol d rising v cc vth 3.8 v vcc under voltage lockout threshold hysteresis v cc hys 5 00 mv vcc regulator v cc 4. 8 v vcc load regulation icc=5ma 0.5 % thermal protection 6) thermal shutdown t sd 150 c thermal shutdown hysteresis 25 c notes : 6) guaranteed by design 7) 100% tested for internal ic prior to module assembly 8) guaranteed by production test and/or characterization for internal ic prior to module assembly
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 7 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. pin functions pin # name description 1, 2, 55, 58, 60 agnd analog/signal ground. i t needs to be connected to gnd on pcb layout. 3 >dc_trim output voltage dc trimming. connect this pin to pin dc_trim> first, and then to the output voltage sense point through a resistor. the resistor value can be chosen based on equation 1. 4,6,23, 32, 44, 49 n/c not connected. keep these pins floating. 5 ac_trim output voltage ac trimming. connect these pins to the output through a capacitor. the capacitor value can be chosen based on equation 2. 7 - 22, 61, 62 sw switch output. keep them floating. 24 - 31, 63 vout module voltage output node. 33 - 43, 64 gnd system power ground. reference ground of the regulated output voltage. pcb layout requires extra care. connect using wide pcb traces. 45 - 48, 65 vin supply voltage. supply power to the internal mosf et and regulator. the mpm3684 operates from a +2.5v to +18v input rail with 5v external bias and from a +4.5v to +18v input rail with internal bias. it requires input decoupling capacitors. connect using wide pcb traces and multiple vias. 50 >freq frequen cy set in. an internal 430k frequency set resistor is used if connecting this pin to pin freq<. keep this pin floating if values other than 300k are needed. 51 en enable. digital input that turns the regulator on or off. drive en high to turn on the regul ator, drive it low to turn it off. connect en to in through a pull - up resistor or a resistive voltage divider for automatic startup. do not float this pin. 52 freq> frequency set out. an internal 430k frequency set resistor is used if connecting this pin to pin freq>. if values other than 430k are needed, connect the resistor between this pin and pin vin. 53 dc_trim> output voltage dc trimming. connect this pin to pin >dc_trim first, and then to the output voltage sense point through a resistor. the resi stor value can be chosen based on equation 1. 54 ss soft start. floating this pin has the default 3ms ss time. the ss time can be extended by connecting an external capacitor between ss and agnd pins. 56 pg power good. the output is an open drain signal. require a pull - up resistor to a dc voltage to indicate high if the output voltage exceeds 91% of the nominal voltage. there is a 2.5ms delay from fb 91% to pg goes high. 57 vcc internal 4.8v ldo output. power the driver and control circuits. keep this pin floating. applying a 5v external bias can disable the internal ldo to boost the efficiency. 59 bst bootstrap. keep this pin floating.
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 8 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. typical performance characteristics v in =12v, v out =1.2v, t a =25?c, unless otherwise noted.
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 9 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. typical performance characteristics (continued) v in =12v, v out =1.2v, t a =25?c, unless otherwise noted.
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 10 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. block diagram f r e q > v c c e n d c _ t r i m > p g i n b s t v o u t p g n d h s - f e t h s d r i v e r l s - f e t l s d r i v e r z c d c u r r e n t m o d u l a t o r l o g i c b s t b i a s f b c o m p a r a t o r u v o v u v d e t e c t c o m p a r a t o r o v d e t e c t c o m p a r a t o r p g o o d c o m p a r a t o r s o f t s t a r t / s t o p r e f e r e n c e v c c l d o o n t i m e r m i n i m u m o f f t i m e r v c c l s c u r r e n t l i m i t a c _ t r i m > d c _ t r i m a g n d s s 4 3 0 k > f r e q 1 0 k 1 k 3 0 0 k 3 0 u f 5 . 7 u f 1 u f
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 11 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. operation power module operation the mpm3684 is a high performance single output synchronous switching mode dc - to - dc power suppl y. it can deliver 15 a continuous output current. the mpm3684 can provide an output voltage from 0.65v to 5v over a 4.5v to 18v (or 2.5v to 18v with 5v external vcc bias) wide input voltage range. the mpm3684 is a complete power solution. it integrates a co nstant - on - time (cot) control dc - to - dc regulator, power devices, an inductor, input/output capacitors and some other supporting resistors and small capacitors. it only needs as few as one external resistor and one external small capacitor to operate. the mp m3684 is controlled by both the vcc voltage and the en signal. it can only be turned on when both voltages are higher than the thresholds. the switching frequency is determined by a frequency set resistor. the default switching frequency with the integrate d resistor is shown in table 1. the default switching frequency increases with the output voltage. the switching frequency can also be programmed externally in the range of 200khz to 1000khz. the details can be found in the section of switching frequency setting on p age 12 . the mpm3684 utilizes constant - on - time control. it has sufficient stability margin with simple loop compensation. and it provides very good transient response with a wide range of output capacitors, even with all ceramic output capacito rs. the mpm3684 has a variable soft start timer to smooth - out the output voltage during start - up. the default (with ss pin floating) soft start timer is about 3ms. the soft - start time can be extended by adding a capacitor between ss pin and agnd pin. pwm o peration the mpm3684 uses constant - on - time (cot) control to provide a fast transient response and eas e loop stabilization. at the beginning of each cycle, the high - side mosfet (hs - fet) turn s on when the feedback voltage ( v fb ) drops below the reference vol tage ( v ref ), which indicates an insufficient output voltage. the input voltage and the frequency - set resistor determine the on period as follows: (1) after the on period elapses, the hs - fet turn s off. it turn s on again when v fb drops below v ref . by repeating this operation, the converter regulates the output voltage to the desired level. the integrated low - side mosfet (ls - fet) t urn s on when the hs - fet is off to minimize the conduction loss. there is a dead short (o r shoot - through) between input and gnd if both hs - fet and ls - fet turn on at the same time. a dead - time (dt) internally generated between hs - fet off and ls - fet on , or ls - fet off and hs - fet on avoids shoot - through . heavy - load operation figure 2 heavy load operation w hen the output current is high and the inductor current is always above zero amps, it is called continuous - conduction - mode (ccm). figure 2 shows t he ccm operation. when v fb is below v ref , hs - fet turn s on for a fixed interval determined by the on e - shot on - timer as per equation 1 . when the hs - fet turn s off, the ls - fet turn s on until the next period. in ccm operation, the switching frequency is fairly constant and is also called pwm mode. freq on in 6.1 r (k ) t (ns) v (v) 0.4 ?? ? ?
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 12 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. light - load operation as the load decreas es , the inductor c urrent decrease s too. when the inductor current touch es zero, the operation is transit ed from continuous - conduction - mode (ccm) to dis continuous - conduction - mode (dcm). figure 3 shows t he light load operation . when v fb drops below v ref , hs - fet turn s on for a fixed interval determined by the one - shot on - timer as per equation 1. when the hs - fet turn s off, the ls - fet turn s on until the inductor current reaches zero. in dcm operation, t he v fb does not reach v ref when the inductor current is approaching zero. th e ls - fet driver turns into tri - state (high z) whenever the inductor current reaches zero. a current modulator takes over the control of ls - fet and limits the inductor current less than - 1ma. hence, the output capacitors discharge slowly to gnd through ls - f et. as a result, this mode improves the efficiency greatly at light load condition . at this condition, the hs - fet does not turn s on as frequently as at heavy load condition. this is called pulse skip mode. at light load or no load condition, the output dro ps very slowly and the mpm3684 reduce s the switching frequency naturally and then achieves high efficiency at light load . figure 3 light load operation as the output current increases from the light load condition, the current modulator regulates the ope rating period that becomes shorter. the hs - fet turn s on more frequently. hence , the switching frequency increases correspondingly. the output current reaches the critical level when the current modulator time decreases to zero. t he critical output current level can be determined as follows: (2) where f sw is the switching frequency. the ic turns into pwm mode once the output current exceeds the critical level. after that, the switching frequency stays fairly constant over the output current range. switching frequency s electi ng the switching frequency requires trad ing off between efficiency and component size. low frequency operation increases efficiency by reducing mosfet switching losses, but requires larger induct or and capacit or values to minimize the output voltage ripple. the mpm3684 uses a daptive c onstant - on - time (cot) control to generate a fairly constant frequency at ccm condition , though the ic lacks a dedicated oscillator. the on time of hsfet can be set by connecting a resistor between in pin and freq pin. its input voltage adaptive. so for a fixed output voltage, the switching frequency stays fairly constant. the switching frequency can be set internally and externally. figure 4 shows that the switching f requency is determined by the internal 430k resistor. the 430k resistor is connected to in pin so that the input voltage is feed - forwarded to the one - shot on - time timer. when operating in steady state at ccm, the duty ratio stays at v out /v in , so the switch ing frequency is fairly constant over the input voltage range. the switching frequency can be determined by equation 3: figure 4 (3) where t delay is the comparator delay of about 5 ns. in out out out sw in (v v ) v i 2 l f v ?? ? ? ? ? 4 3 0 k 4 0 2 m p m 3 6 8 4 i n f r e q > > f r e q o n t i m e r 6 sw in delay in out 10 f (khz) v (v) 6.1 430(k ) t (ns) v (v) 0.4 v (v) ? ?? ?? ?
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 13 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. table 1 shows the switching frequency with different common output voltages: table 1 if a switching frequency other than those listed in table 1 is desired, an external frequency set resistor can be connected as shown in figure 5: figure 5 the switching frequency can be estimated through equation (4) as follows: (4 ) where t delay is the comparator delay of about 5 ns. typically , the mpm3684 is set to 200khz to 1mhz application s . thanks to its monolithic structure, the mpm3684 is optimized to operate at high switching frequenc ies at high efficiency . h igh switching frequenc ies allow for physically small er lc filter components to reduce the pcb footprint . configuring the en control the power module turns on when e n goes high ; conversely it turns off when en goes low . do not float the pin. for automatic start - up , pull the en pin up to input voltage through a resistive voltage divider. choose the values of the pull - up resistor (r up from the in pin to the en pin) and th e pull - down resistor (r down from the en pin to gnd) to determine the automatic start - up voltage: ( 5 ) for example, for r up =100k and r down =51k, the v in - start is set at 4. 44 v. to reduce noise, a dd a 10nf ce ramic capacitor from en to gnd. a n internal zener diode on the en pin clamps the en pin voltage to prevent run ning away. the maximum pull up current ( assuming the worst case 6v for the internal zener clamp ) should be limited to 1ma or less . therefore , w hen driving en with an external logic signal, the driving voltage should be less than 6v . w hen connecting en to in through a pull - up resistor or a resistive voltage divider, select a resistance that ensure s a maximum pull - up current of 1ma. if using a resisti ve voltage divider and v in exceeds 6v, then the minimum resistance for the pull - up resistor r up should meet: (6 ) with only r up (the pull - down resistor , r down , is not connected), the n the vcc uvlo th reshold determines v in - start , so the minimum resistor value is: (7 ) a typical pull - up resistor is 100k. vcc power supply the mpm3684 has an internal vcc ldo to supply the power to the internal circuits and drives the power devices. this vcc ldo is derived from the input supply. to ensure proper operation, the minimum inpu t voltage should be 4.5v. an external 5v vcc bias can disable the internal ldo. in this case, vin can be as low as 2.5v. the efficiency can be higher with external 5v vcc bias. figure 6 shows the comparison. vo (v) fs(khz) 1 400 1.2 500 1.5 600 1.8 700 r f r e q 4 3 0 k 4 0 2 m p m 3 6 8 4 i n f r e q > > f r e q o n t i m e r 6 sw freq in delay in out 10 f (khz) 6.1 r (k ) v (v) t (ns) v (v) 0.4 v (v) ? ?? ?? ? up down in start down (r r ) v 1.5 (v) r ? ? ?? in up down v 6v 6v 1ma rr ? ?? in up v 6v r ( ) 1ma ? ??
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 14 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. figure 6 soft start the mpm3684 employ s a soft start (ss) mechanism to ensure a smooth output during power - up. when the en pin goe s high, an internal current source ( 20 a) charges the ss capacitor . the ss capacitor voltage takes over the ref voltage to the pwm comparator. the output voltage smoothly ramps up with the ss voltage. once the ss voltage reaches the ref voltage, it continue s ramping up while v ref takes over th e pwm comparator. at this point, soft start finishes and the device enters steady state operation. an internal 100nf ss capacitor is used. so the default (with ss pin floating) ss time can be estimated as: (8) so the default ss time is about 3ms. if longer ss time is needed, an external ss capacitor can be added between ss pin and agnd pin. the external capacitor value can be determined as follows: (9) pre - bias startup the mpm3684 has bee n designed for monotonic startup into pre - biased loads. if the output is pre - biased to a certain voltage during startup, the ic will disable switching for both high - side and low - side switches until the voltage on the soft - start capacitor exceeds the sens ed output voltage at the fb pin . power good (pg) the mpm3684 ha s a power - good (pg) output. the pg pin is the open drain of a mosfet. c onnect it to v cc or some other voltage source that measures less than 5.5v through a pull - up resistor ( typically 100 k? ). after applying the input voltage, the mosfet turn s on so that the pg pin is pulled to gnd before the ss is ready. after the fb voltage reaches 9 1 % of the ref voltage, the pg pin is pulled high after a 2.5ms delay. when the fb voltage drops to 80 % of the ref voltage or exceeds 120% of the nominal ref voltage , the pg pin is pulled low. if the input supply fails to power the mpm3684, the pg pin is also pulled low even though this pin is tied to an external dc source through a pull - up resistor. over - curre nt protection (ocp) the mpm3684 features two current limit levels for over - current conditions: low - side valley current limit and low - side negative current limit. low - side valley current limit : the device monitors the inductor current during the ls - fet on state. if the ls - fet sourcing current is higher than the internal positive - valley - current limit, the hs - fet remains off and the ls - fet remains on for the next on time. when the ls - fet sourcing current drops below the valley current limit, then the ls - fet turns off and the hs - fet turns on again. the mpm3684 enters ocp non - latch protection mode if the ls - fet sourcing valley current keeps exceeding the valley current limit for a certain period of time. during ocp , the device tries to recover from the over - cur rent fault with hiccup mode: the chip disable s the output power stage, discharge s the soft - start capacitor and then automatically retries soft - start. the device repeats this operation cycle as long as the over - current condition still exists. when the over - current condition disappea rs, the mpm3684 initiates a new ss to rise back to regulation level . 75 77 79 81 83 85 87 89 91 93 95 0 3 6 9 12 15 effi. (%) output current (a) mpm3684 efficiency (12v to 1.2v 500khz) external vcc internal vcc ref ss ss 100(nf) v (v) t (ms) i (ua) ? ? ss ss ss ref t (ms) i (ua) c (nf) 100(nf) v (v) ? ??
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 15 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. low - side negative current limit : if the sensed ls - fet negative current exceeds the negative current limit, the ls - fet turns off immediately and stays off for t he remainder of the off period. in this situation, both mosfets are off until the end of a fixed interval. the hs - fet body diode conducts the inductor current for the fixed time. over - v oltage protection (ovp) the mpm3684 monitor s the output voltage using the fb pin connected to the tap of a resistor divide r to detect over - voltage . it provides non - latch ovp mode. if the fb voltage exceeds the nominal ref voltage but remains lower than 120% of the ref voltage (0. 6 11 v) , both mosfets are off. if t he fb voltage exceeds 12 0 % of the ref voltage but remains below 130% , the ls - fet turn s on while the hs - fet remains off. the ls - fet remain s on until the fb voltage drops below 1 1 0 % of the ref voltage or the low - side negative current limit is hit . if the fb voltage exce eds 130% of the ref voltage, it enters a non - latch mode. the ls - fet remains on until the fb voltage drops below 110% of the ref voltage, and the mpm3684 initiates a new ss to rise back to regulation level and operates normally again. uvlo protection the mp m3684 ha s under - voltage lock - out protection (uvlo). when the vcc voltage exceeds the uvlo rising threshold, the mpm3684 power s up. it shuts off when the vcc voltage falls below the uvlo falling threshold voltage. this is non - latch protection. the mpm3684 i s disabled when the vcc voltage falls below 3.3 v. if an application requires a higher uvlo threshold , use the two external resistors connected to the en pin as shown in figure 9 to adjust the startup input voltage. for best results, use the enable resisto rs to set the input voltage falling threshold (v stop ) above 3.6 v. set t he rising threshold (v start ) to provide enough hysteresis to account for any input supply variations. figure 7 adjustable uvlo threshold thermal shutdown t he mpm3684 has thermal shu tdown . the ic internal ly monitor s the junction temperature. if the junction temperature exceeds the threshold value ( minimum 150oc), the converter shuts off. this is a non - latch protection. there is about 25oc hysteresis. once the junction temperature drop s to about 125oc, it initiates a soft startup . en comparator r up r down in en
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 16 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. application informat ion setting the output voltage - small esr capacitors when the output capacitors are all ceramic capacitors or capacitors with small esr, external ramp is injected through the r/c network across the inductor. the circuit connection is as follows: figure 8 here is the procedure to find the values for ctrim and rtrim: a) determine the ton (10) b) determine ctr im. choose a v ramp around 10mv - 30mv for most of the applications. (11) c) find the average feedback voltage v fb (12) d) calculate rtrim to get the desired output voltage: (13) (14) setting the output voltage - large esr capacitors if one or more piece of the output capacitors have large esr, then there is no need of external ramp. otherwise, itll generat e group pulses at light load conditions. the ctrim is still recommended to boost the phase margin of the system. a value between 100pf and 2.2nf is recommended. the circuit connection can be made as the following: figure 9 the r trim can be determined as follows to obtain the desired output voltage: (15) input capacitor the input current to the step - down power module is discontinuous , and t herefore, it requires a capacitor to sup ply the ac current to the step - down power module while maintaining the dc input voltage. use c eramic capacitors for best performance. during layout, place the input capacitors as close to the in and gnd pin s as possible. the capacitance can var y significa ntly with temperature. use c apacitors with x5r or x7r ceramic dielectrics because they are fairly stable over a wide temperature range . the capacitors must also have a ripple current rating that exceeds the converters maximum input ripple current. estimate t he input ripple current as follows: ( 16 ) the worst - case condition occurs at v in = 2v out , where: ( 17 ) m p m 3 6 8 4 r 3 3 0 0 k 4 0 2 s w f b r 2 1 k 4 0 2 r 1 1 0 k 4 0 2 a g n d d c _ t r i m > a c _ t r i m v o u t > d c _ t r i m r t r i m c t r i m l c o u t freq on in 5.3 r (k ) t (ns) v (v) 0.4 ?? ? ? ) ns ( t ) v ( v ) k ( r ) v ( v ) v ( v ) pf ( c on ramp out in trim ? ? ? ? ? 3 ramp fb _ avg ref v (v) v (v) v (v) 2 ?? ) k ( ) ) v ( v ) v ( v ( ) k ( r avg _ fb out o ? ? ? ? ? 10 1 o trim o r (k ) 300(k ) r (k ) 300(k ) r (k ) ? ? ? ?? ? ? ? m p m 3 6 8 4 r 3 3 0 0 k 4 0 2 s w f b r 2 1 k 4 0 2 r 1 1 0 k 4 0 2 a g n d d c _ t r i m > a c _ t r i m v o u t > d c _ t r i m r t r i m c t r i m l c o u t out ref trim ref vv r (k ) 10 v ? ? ? ? ) v v 1 ( v v i i in out in out out cin ? ? ? ? 2 i i out cin ?
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 17 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. for simplification, choose an input ca pacitor with an rms current rating that exceeds half the maximum load current. the input capacitance value determines the converter input voltage ripple. select a capacitor value that meets any input voltage ripple requirement s. estimate t he input voltage ripple as follows: ( 18 ) the worst - case condition occurs at v in = 2v out , where: ( 19 ) pcb layout recommendations 1. place the input/output capacitors on the same side of the mpm3684, and as cl ose to the mpm3684 package as possible. 2. a solid system ground layer is required to be placed immediately below the surface layer with the mpm3684. 3. thermal vias (18 mil diameter and 8 mil hole size) are required to be placed underneath the gnd, in and vout pads, as well as the edges of the mpm3684 and the input/output capacitors. 4. keep the dc_trim traces as short as possible. figure 10 ) v v 1 ( v v c f i v in out in out in sw out in ? ? ? ? ? ? in sw out in c f i 4 1 v ? ? ? ? c i n 1 c i n 2 c o u t 1 c o u t 2 s w r t r i m c t r i m m p m 3 6 8 4 i n v o u t g n d c o u t 3 c i n 3 g n d g n d g n d g n d v i n v i n g n d g n d g n d g n d g n d g n d g n d n / c v o u t v i n n / c p g v c c a g n d s s a g n d e n > f e r q v i n d c _ t r i m > f r e q > a g n d n / c b s t a c _ t r i m n / c s w s w s w s w s w s w s w s w a g n d a g n d s w s w > d c _ t r i m n / c s w v o u t s w s w s w s w n / c v o u t v o u t v o u t v o u t v o u t v o u t s w
mpm3684 C 18v 15 a step - down power module mpm3684 rev. 1.0 2 www.monolithicpower.com 18 11/30/2016 mps proprietary information. patent protected. unauthorized phot ocopy and duplication prohibited. ? 2016 mps. all rights reserved. typical design parameter table the following table (table 2) include s the recommen ded component val ues for typical designs . ref vin (v) vout (v) rtrim (k ? ) ctrim (pf) rfreq (k ? ) fs (khz) cout (uf) ripple (mv) 1 12 1 6.49 560 ns 400 5x47 11.6 2 12 1 6.49 560 ns 400 3x47 16.4 3 12 1 6.49 560 300 600 5x47 5.0 4 12 1 6.49 560 300 600 3x47 7.6 5 12 1 6.49 220 178 1000 3x47 3.8 6 12 1 6.49 330 178 1000 5x4 7 2.2 7 12 1.2 10 560 649 300 5x47 24.0 8 12 1.2 10 560 649 300 3x47 38.4 9 12 1.2 10 560 ns 500 5x47 11.2 10 12 1.2 10 560 ns 500 3x47 14.8 11 12 1.2 10 270 200 1000 5x47 3.2 12 12 1.2 10 270 200 1000 3x47 4.6 13 12 1.5 15 680 806 300 5x47 32.8 14 12 1.5 15 680 806 300 3x47 46.0 15 12 1.5 15 560 ns 600 5x47 8.4 16 12 1.5 15 560 ns 600 3x47 11.6 17 12 1.5 15.8 330 243 1000 5x47 5.8 18 12 1.5 15.8 330 243 1000 3x47 7.0 19 12 1.8 21 560 750 400 5x47 25.4 20 12 1.8 21 560 750 400 3x47 49.6 21 12 1.8 21 560 ns 750 5x47 7.6 22 12 1.8 21 560 ns 750 3x47 9.4 23 12 1.8 21 470 301 1000 5x47 8.8 24 12 1.8 21 330 301 1000 3x47 12.4 25 12 2.5 34 680 1000 400 5x47 34.2 26 12 2.5 34 680 1000 400 3x47 46.4 27 12 2.5 35.7 680 715 600 5x47 18.8 28 12 2. 5 35.7 680 715 600 3x47 25.2 29 12 2.5 34 330 432 1000 5x47 9.8 30 12 2.5 34 270 432 1000 3x47 13.0 33 12 3.3 49.9 330 1000 600 5x47 31.6 34 12 3.3 49.9 330 1000 600 7x47 21.2 35 12 3.3 49.9 270 549 1000 5x47 6.0 36 12 3.3 49.9 270 549 1000 3x47 10.2 39 12 5 90.9 390 1500 600 5x47 49.2 40 12 5 90.9 390 1500 600 7x47 36.0 41 12 5 90.9 180 909 1000 5x47 20.8 42 12 5 90.9 150 909 1000 3x47 28.8 table 2: typical design examples
mpm3684 C 18v 15 a step - down power module notice: the information in this document is subject to change without 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. mpm3684 rev. 1.0 2 www.monolithicpower.com 19 11/30/2016 mps proprietary information. patent protected. unauthorized photocopy and duplication prohibited. ? 2016 mps. all rights reserved. package information qfn - 65 (12mm x 15mm x 4mm)

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