View NB634EL_9030987.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

nb634 high efficiency 5a, 24v, 500khz synchronous step -down converter nb634 rev. 0.94 www.monolithicpower.com 1 12/25/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. the future of analog ic technology description the nb634 is a high efficiency synchronous rectified step-down switch mode converter with built-in internal power mosfets. it offers a very compact solution to achieve 5a continuous output current over a wide input supply range with excellent load and line regulation. the nb634 operates at high efficiency over a wide output current load range. current mode operation provides fast transient response and eases loop stabilization. full protection features include latch-off ocp and thermal shut down. the nb634 requires a minimum number of readily available standard external components and is available in a space saving qfn14 (3mm x 4mm) package. features ? wide 4.5v to 24v operating input range ? 5a output current ? low r ds (on) internal power mosfets ? proprietary switching loss reduction technique ? fixed 500khz switching frequency ? sync from 300khz to 2mhz external clock ? internal compensation ? latch-off ocp protection and thermal shutdown ? output adjustable from 0.8v ? available in a qfn14 (3mmx4mm) package applications ? notebook systems and i/o power ? networking systems ? digital set top boxes ? personal video recorders ? flat panel television and monitors ? distributed power systems all 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 o f monolithic power systems, inc. typical application for notebook 10 2,3,4,5 12,13,14 r2 8.06k rt 24.9k l1 2.3uh nb634 sw gnd fb en/sy nc in bst vcc aam c3 0.1uf r3 r4 c1 22uf 4.5v-24v c4 0.1uf c2 47uf r1 10k vin vout 1.8v on/off 6 8 1 7 11 3.3v vcc 9 pg output current (a) efficiency(%) efficiency v out =1.8v, l=1.0uh 50 55 60 65 70 75 80 85 90 95 100 0123456 v in =12v v in =7v v in =24v
nb634 ?high efficiency, 5a, 24v, 500khz synchronous step-down converter nb634 rev. 0.94 www.monolithicpower.com 2 12/25/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. ordering information part number* package top marking free air temperature (t a ) NB634EL qfn14 (3mmx4mm) 634e -20 ? c to +85 ? c * for tape & reel, add suffix ?z (eg. NB634EL?z); for rohs compliant packaging, add suffix ?lf (eg. NB634EL?lf?z) package reference top view in sw sw sw sw bst en/sync 1 2 3 4 5 6 7 agnd gnd gnd vcc aam pg fb 14 13 12 11 10 9 8 exposed pad on backside absolute maxi mum ratings (1) supply voltage v in ....................................... 28v v sw ...........................-0.3v (-5v for 10ns) to 28v v bs ....................................................... v sw + 6v all other pins ..................................-0.3v to +6v continuous power dissipation (t a = +25c) (2) ???????????????????2.6w junction temperature ...............................150 ? c lead temperature ....................................260 ? c storage temperature............... -65 ? c to +150 ? c recommended operating conditions (3) supply voltage v in ...........................4.5v to 24v maximum junction temp. (t j ) ................+125 ? c thermal resistance (4) ja jc qfn14(3mmx4mm) ................48 ...... 11 ... ? 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.
nb634 ?high efficiency, 5a, 24v, 500khz synchronous step-down converter nb634 rev. 0.94 www.monolithicpower.com 3 12/25/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. electrical characteristics v in = 12v, t a = +25 ? c, unless otherwise noted. parameters symbol condition min typ max units supply current (shutdown) i in v en = 0v 2 a supply current (quiescent) i in v en = 2v, v fb = 1v 1 ma hs switch on resistance (5) hs rds-on 120 m ? ls switch on resistance (5) ls rds-on 20 m ? switch leakage sw lkg v en = 0v, v sw = 0v or 12v 0 10 a current limit i limit 7 a oscillator frequency f sw v fb = 0.75v 350 500 650 khz fold-back frequency f fb v fb = 100mv 0.25 f sw maximum duty cycle d max v fb = 700mv 85 90 % sync frequency range f sync 0.3 2 mhz feedback voltage v fb 785 805 825 mv feedback current i fb v fb = 805mv 10 50 na en/sync input low voltage vil en 0.4 v en/sync input high voltage vih en 2 v en input current i en v en = 2v 2 a en turn off delay en td-off 5 s power good rising threshold pg vth-hi 0.9 v fb power good falling threshold pg vth-lo 0.7 v fb power good delay pg td 250 s power good sink current capability v pg sink 4ma 0.4 v power good leakage current i pg_leak v pg = 3.3v 10 na v in under voltage lockout threshold rising inuv vth 3.8 4.0 4.2 v v in under voltage lockout threshold hysteresis inuv hys 880 mv vcc regulator v cc 5 v vcc load regulation icc=5ma 5 % thermal shutdown t sd 150 c note: 5) guaranteed by design.
nb634 ?high efficiency, 5a, 24v, 500khz synchronous step-down converter nb634 rev. 0.94 www.monolithicpower.com 4 12/25/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. pin functions pin # name description 1 in supply voltage. the nb634 operates from a +4.5v to +24v input rail. c1 is needed to decouple the input rail. use wide pcb traces and multiple vias to make the connection. 2,3,4,5 sw switch output. use wide pcb traces and multiple vias to make the connection. 6 bst bootstrap. a capacitor connected between sw and bst pins is required to form a floating supply across the high-side switch driver. 7 en/sync en=1 to enable the nb634. external clock can be applied to en pin for changing switching frequency. for automatic start- up, connect en pin to vin with 100k ? resistor. it includes an internal 1m ? pull-down resistor. 8 fb feedback. an external resistor divider fr om the output to gnd, tapped to the fb pin, sets the output voltage. to prevent current limit r un away during a short circuit fault condition, the frequency fold-back comp arator lowers the oscillator frequency when the fb voltage is below 100mv. 9 pg power good output. the output of this pin is an open drain. when the fb voltage rises to 90% of the ref voltage, power good (pg) output goes high after a 250 s delay. when the fb voltage drops to 70% of the ref voltage, pg goes low immediately. 10 aam connects to a voltage set by a resistor divider between v cc and gnd to force the nb634 into non-synchronous mode at light load. 11 vcc bias supply. decouple with 0.1f capacitor. 14 agnd analog ground. this pin is the referenc e ground of the regulated output voltage. for this reason care must be taken in pcb layout. 12, 13 gnd, exposed pad system ground. connect these pins wi th larger copper areas to the negative terminals of the input and output capaci tors. connect exposed pad to gnd plane for proper thermal performance.
nb634 ?high efficiency, 5a, 24v, 500khz synchronous step-down converter nb634 rev. 0.94 www.monolithicpower.com 5 12/25/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. typical performanc e characteristics v in =12v, v out =1.8v, l=1.0h, t a =+25c, unless otherwise noted. -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 550 555 560 565 570 575 580 585 590 peak current vs. duty cycle duty cycle(%) peak current(a) input voltage (v) output voltage (v) operating range 0 1 2 3 4 5 6 7 8 9 10 020406080100 0.1 1 10 100 0 5 10 15 20 25 load regulation normalized output voltage (%) output current (a) input voltage (v) normalized output voltage (%) output current (a) line regulation case temperature rise vs. output current output current (a) efficiency(%) efficiency v out =1.8v, l=1.0uh 50 55 60 65 70 75 80 85 90 95 100 0123456 v in =7v v in =12v v in =24v -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0 5 10 15 20 25 i o =5a i o =2.5a 0123456 0123456 dmax limit minimun on time limit v in =12v v in =7v v in =24v quiescent current vs. input voltage input voltage (v) input voltage (v) shutdown current vs. input voltage vcc(v) input voltage (v) vcc regulator line regulation 0 5 10 15 20 25 3.5 4.0 4.5 5.0 5.5 0 5 10 15 20 25 0 5 10 15 20 25 v fb =1v -0.1 -0.05 0 0.05 0.1 i out =0a 0 10 20 30 40 50
nb634 ?high efficiency, 5a, 24v, 500khz synchronous step-down converter nb634 rev. 0.94 www.monolithicpower.com 6 12/25/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. typical performanc e characteristics (continued) v in =12v, v out =1.8v, l=1.0h, t a =+25c, unless otherwise noted. 2ms/div output ripple voltage i out =5a v out 1v/div v en 10v/div v out 1v/div v en 10v/div v sw 10v/div v sw 10v/div i inductor 1a/div i inductor 5a/div v out 1v/div v en 10v/div v sw 10v/div i inductor 5a/div v out /ac 50mv/div v sw 10v/div i out 2a/div v out 1v/div v sw 10v/div i inductor 5a/div v out / ac 10mv/div v sw 10v/div i inductor 5a/div v out 1v/div v en 10v/div v sw 10v/div i inductor 500ma/div 2ms/div 400ms/div 1ms/div enable startup i out =0a enable shut down i out =0a enable shut down i out =5a enable startup i out =5a short circuit protection 20us/div 1us/div 100us/div load transient response i out =0.5a-4.5a@ 2.5a/us i inductor 5a/div v out 1v/div v in 10v/div pg 2v/div 1ms/div pg delay @ start up 250us delay 250us 90% v out
nb634 ?high efficiency, 5a, 24v, 500khz synchronous step-down converter nb634 rev. 0.94 www.monolithicpower.com 7 12/25/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. block diagram 50pf 1meg bst rsen in oscillator 250us delay vcc regulator boost regulator pg comparator vcc currrent sense amplifer vcc pg current limit comparator error amplifier reference en/sync fb + + - + - + - + - aam sw gnd ls driver hs driver comparator on time control logic control 1pf 400k figure 1?functional block diagram
nb634 ?high efficiency, 5a, 24v, 500khz synchronous step-down converter nb634 rev. 0.94 www.monolithicpower.com 8 12/25/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. operation the nb634 is a high efficiency synchronous rectified step-down switch mode converter with built-in internal power mosfets. it offers a very compact solution to achieve more than 5a continuous output current over a wide input supply range with excellent load and line regulation. the nb634 operates in a fixed frequency, peak current control mode to regulate the output voltage. a pwm cycle is initiated by the internal clock. the integrated high-side power mosfet is turned on and remains on until its current reaches the value set by the comp voltage. when the power switch is off, it remains off until the next clock cycle starts. if, in 90% of one pwm period, the current in the power mosfet does not reach the comp set current value, the power mosfet will be forced to turn off. error amplifier the error amplifier compares the fb pin voltage with the internal 0.8v reference (ref) and outputs a current proportional to the difference between the two. this output current is then used to charge or discharge the internal compensation network to form the comp voltage, which is used to control the power mosfet current. the optimized internal compensation network minimizes the external component counts and simplifies the control loop design. enable/sync control the nb634 has a dedicated enable/sync control pin (en/sync). by pulling it high or low, the ic can be enabled and disabled. tie en to vin through a resistor for automatic start up. to disable the part, en must be pulled low for at least 5s. the nb634 can be synchronized to an external clock ranging from 300 khz to 2mhz through the en/sync pin. the internal clock rising edge is synchronized to the external clock rising edge. under-voltage lockout (uvlo) under-voltage lockout (uvlo) is implemented to protect the chip from operating at insufficient supply voltage. the nb634 uvlo comparator monitors the output voltage of the internal regulator, vcc. the uvlo rising threshold is about 4.0v while its falling threshold is a consistent 3.2v. internal soft-start the soft-start is implemented to prevent the converter output voltage from overshooting during startup. when the chip starts, the internal circuitry generates a soft-start voltage (ss) ramping up from 0v to 1.2v. when it is lower than the internal reference (ref), ss overrides ref so the error amplifier uses ss as the reference. when ss is higher than ref, ref regains control. over-current protection and latch-off the nb634 has cycle-by-cycle overcurrent limit when the inductor current peak value exceeds the set current limit threshold. when output voltage drops below 70% of the reference, and inductor current exceeds the current limit. the nb634 will be latched off. this is especially useful to ensure system safety under fault condition. the nb634 clears the latch once the en or input power is recycled. the latch-off function is disabled during soft-start duration. thermal shutdown thermal shutdown is implemented to prevent the chip from operating at exceedingly high temperatures. when the silicon die temperature is higher than 150 ? c, it shuts down the whole chip. when the temperature is lower than its lower threshold, typically 140 ? c, the chip is enabled again.
nb634 ?high efficiency, 5a, 24v, 500khz synchronous step-down converter nb634 rev. 0.94 www.monolithicpower.com 9 12/25/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. floating driver and bootstrap charging the floating power mosfet driver is powered by an external bootstrap capacitor. this floating driver has its own uvlo protection. this uvlo?s rising threshold is 2.2v with a hysteresis of 150mv. the bootstrap capacitor voltage is regulated internally by vin through d1, m1, c4, l1 and c2 (figure 2). if (vin-vsw) is more than 5v, u1 will regulate m1 to maintain a 5v bst voltage across c4. v in v out d1 m1 bst c4 l1 sw u1 5v c2 figure 2?internal bootstrap charging circuit startup and shutdown if both vin and en are higher than their respective thresholds, the chip starts. the reference block starts first, generating stable reference voltage and currents, and then the internal regulator is enabled. the regulator provides stable supply for the remaining circuitry. three events can shut down the chip: en low, vin low and thermal shutdown. in the shutdown procedure, the signal path is first blocked to avoid any fault triggering. the comp voltage and the internal supply rail are then pulled down. the floating driver is not subjected to this shutdown command.
nb634 ?high efficiency, 5a, 24v, 500khz synchronous step-down converter nb634 rev. 0.94 www.monolithicpower.com 10 12/25/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. application information setting the output voltage the external resistor divider is used to set the output voltage (see typical application on page 1). the feedback resistor r1 also sets the feedback loop bandwidth with the internal compensation capacitor (see typical application on page 1). choose r1 to be around 10k ? . r2 is then given by: out r1 r2 v 1 0.805v ? ? (1) the t-type network is highly recommended when vo is low, as figure 3 shows. fb 8 rt r2 r1 vout figure 3? t-type network table 1 lists the recommended t-type resistors value for common output voltages. table 1?resistor selection for common output voltages v out (v) r1 (k ? ) r2 (k ? ) rt (k ? ) 1.05 3.09(1%) 10(1%) 24.9(1%) 1.2 4.99(1%) 10(1%) 24.9(1%) 1.8 10(1%) 8.06(1%) 24.9(1%) 2.5 10(1%) 4.75(1%) 24.9(1%) 3.3 10(1%) 3.16(1%) 24.9(1%) 5 10(1%) 1.91(1%) 24.9(1%) selecting the inductor a 1h to 10h inductor with a dc current rating of at least 25% percent higher than the maximum load current is recommended for most applications. for highest efficiency, the inductor dc resistance should be less than 15m ? . for most designs, the inductance value can be derived from the following equation. out in out 1 in l v(vv) l vifsw ?? ? ?? ? (2) where i l is the inductor ripple current. choose inductor current to be approximately 30% of the maximum load current. the maximum inductor peak current is: 2 i i i l load ) max ( l ? ? ? (3) under light load conditions below 100ma, larger inductance is recommended for improved efficiency. setting the aam voltage the aam voltage is used for setting the transition point from aam to ccm. it should be chosen to provide the best combination of efficiency, stability, ripple, and transient. if the aam voltage is set lower, then stability and ripple improve, but efficiency during aam mode and transient degrade. likewise, if the aam voltage is set higher, then the efficiency during aam and transient improve, but stability and ripple degrade. therefore, an optimal aam voltage that provides good efficiency, stability, ripple, and transient needs to be determined. as figure 4 shows, aam voltage can be set by using a resistor divider. r6 r5 vcc(5v) aam figure 4? aam network refer to figure 5 to select an optimal voltage and then use the equation below to determine the value of r6. assume r5 to be around 10k ? . generally, choose r5 to be around 10 k ? , r6 is then determined by the following equation: ? ? ? ? ? ? ? ? 1 aam vcc r5 r6 (4)
nb634 ?high efficiency, 5a, 24v, 500khz synchronous step-down converter nb634 rev. 0.94 www.monolithicpower.com 11 12/25/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 aam (v) v o =1.05v v o =1.8v v o =3.3v v o =5v figure 5? aam selection for common output voltages (v in =7v-24v) selecting the input capacitor the input current to the step-down converter is discontinuous, therefore a capacitor is required to supply the ac current to the step-down converter while maintaining the dc input voltage. use low esr capacitors for the best performance. ceramic capacitors with x5r or x7r dielectrics are highly recommended because of their low esr and small temperature coefficients. for most applications, a 22f capacitor is sufficient. since the input capacitor (c1) absorbs the input switching current, it requires an adequate ripple current rating. the rms current in the input capacitor can be estimated by: ? ? ? ? ? ? ? ? ? ? ? ? in out in out load 1 c v v 1 v v i i (5) the worst case condition occurs at vin = 2vout, where: 2 i i load 1 c ? (6) for simplification, choose the input capacitor whose rms current rating is greater than half of the maximum load current. the input capacitor can be electrolytic, tantalum or ceramic. when using electrolytic or tantalum capacitors, a small, high quality ceramic capacitor, i.e. 0.1 f, should be placed as close to the ic as possible. when using ceramic capacitors, make sure that they have enough capacitance to provide sufficient charge to prevent excessive voltage ripple at input. the input voltage ripple caused by capacitance can be estimated by: load out out in in sw in iv v v1 fc1v v ?? ?? ? ?? ?? ? ?? (7) selecting the output capacitor the output capacitor (c2) is required to maintain the dc output voltage. ceramic, tantalum, or low esr electrolytic capacitors are recommended. low esr capacitors are preferred to keep the output voltage ripple low. the output voltage ripple can be estimated by: out out out esr sw 1 in sw vv 1 v1r fl v 8fc2 ?? ?? ?? ?? ? ? ?? ?? ??? ?? ?? (8) where l 1 is the inductor value and resr is the equivalent series resistance (esr) value of the output capacitor. in the case of ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance. the output voltage ripple is mainly caused by the capacitance. for simplification, the output voltage ripple can be estimated by: out out out 2 sw 1 in vv v1 8f l c2 v ?? ??? ?? ??? ?? (9) in the case of tantalum or electrolytic capacitors, the esr dominates the impedance at the switching frequency. for simplification, the output ripple can be approximated to: out out out esr in sw 1 vv v1r fl v ?? ???? ?? ? ?? (10) the characteristics of the output capacitor also affect the stability of the regulation system. the nb634 can be optimized for a wide range of capacitance and esr values.
nb634 ?high efficiency, 5a, 24v, 500khz synchronous step-down converter nb634 rev. 0.94 www.monolithicpower.com 12 12/25/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. external bootstrap diode an external bootstrap diode may enhance the efficiency of the regulator, the applicable conditions of external bst diode are: ? v out is 5v or 3.3v; and ? duty cycle is high: d= in out v v >65% in these cases, an external bst diode is recommended from the vcc pin to bst pin, as shown in figure 6. sw bst nb634 c l bst c out external bst diode vcc in4148 figure 6?add optional external bootstrap diode to enhance efficiency the recommended external bst diode is in4148, and the bst cap is 0.1~1 f. pc board layout the high current paths (gnd, in and sw) should be placed very close to the device with short, direct and wide traces. the input capacitor needs to be as close as possible to the in and gnd pins. the external feedback resistors should be placed next to the fb pin. keep the switching node sw short and away from the feedback network. en agnd vcc 14 12 11 10 9 8 1 2 3 4 5 6 7 pg in fb sw sw sw sw bst aam gnd c2 l1 r1 rt c1 gnd r3 c3 r2 r4 r5 c4 13 gnd top layer bottom layer figure 7?pcb layout
nb634 ?high efficiency, 5a, 24v, 500khz synchronous step-down converter notice: the information in this document is subject to change wi thout notice. users should warra nt and guarantee that third party intellectual property rights are not infringed upon w hen integrating mps products into any application. mps will not assume any legal responsibility for any said applications. nb637 rev. 0.94 www.monolithicpower.com 13 12/25/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. package information qfn14 (3mm x 4mm) side view top view 1 14 87 bottom view 2. 90 3. 10 1.60 1.80 3.90 4.10 3.20 3.40 0.50 bsc 0.18 0.30 0.80 1.00 0.00 0.05 0.20 ref pin 1 id marking 1.70 0.50 0.25 recommended land pattern 2.90 note: 1) all dimensions are in millimeters . 2) exposed paddle size does not include mold flash . 3) lead coplanarity shall be 0.10 millimeter max. 4) jedec reference is mo-229, variation vged-3. 5) drawing is not to scale. pin 1 id see detail a 3.30 0.70 pin 1 id option b r0.20 typ. pin 1 id option a 0.30x45 o typ. detail a 0.30 0.50 pin 1 id index area

▲Up To Search▲

Price & Availability of NB634EL

	To Download NB634EL Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .