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1 www.semtech.com SC339 ultra low output voltage linear fet controller power management sept 11, 2006 description features the SC339 is an ultra-low output voltage, linear power supply controller designed to simplify power manage- ment for notebook pcs. it is part of semtech?s smart ldo tm family of products. the SC339 has a user adjustable output that can be set anywhere between 0.5v and 3.3v using two external resistors. SC339 features include tight output voltage regulation ( 1% over 0c to +85c), enable control, open drain power good signal, under-voltage protection and soft-start. the enable pin allows the part to enter a very low power standby mode. pulling it high enables the output. the power good pin is an open drain and asserts low when the voltage at the adjust pin is below 88% (typ) of nominal. if the voltage at the adjust pin is below 50% (typ) of nominal, the under- voltage protection circuitry will shut down the output. the SC339 is available in a tiny sot-23 6-pin surface mount package. 1% voltage accuracy over-temperature low shutdown current runs off 5v supply ultra-fast transient response enable control for the output power good monitoring and signaling for the output gate drive from input supply enables use of n-channel mosfet user selectable dropout voltage under-voltage protection for the output sot-23 6-pin surface mount package compatible with ceramic capacitors low ripple output internal 1ms soft-start requires no external compo- nents fully weee and rohs compliant notebook pcs desktop computers battery powered devices portable instruments typical application circuit applications 1.05v @ 3a SC339 in drv adj pgd en gnd c1 c2 c4 5v in 1.05v enable 1.05v power good 1.2v +/-5% in irf7311 or similar v out = (1+r1/r2)*0.5 notes: (1) optional components to use with ceramic output capacitors (c2) c3 (1) r3 (1) r1 r2
2 ? 2006 semtech corp. www.semtech.com SC339 preliminary power management absolute maximum ratings parameter symbol maximum units input supply voltage v in -0.3 to +6 v drive pin v drv -0.3 to v in + 0.3v v adjust and power good pin v adj , v pgd -0.3 to v in + 0.3v v enable pin v en -0.3 to v in + 0.3v v thermal impedance junction to ambient ja 190 c/w thermal impedance junction to case jc 81 c/w operating ambient temperature range t a -40 to +85 c operating junction temperature range t j -40 to +125 c storage temperature range t stg -65 to +150 c lead temperature (soldering) 10 sec. t lead 300 c esd rating (human body model) v esd 2kv electrical characteristics unless speci ed: t a = 25c, v in = v en = 5v 5%, v pwr (1) = 1.5v 5%, 0a i out 3a. values in bold apply over full operating ambient temperature range. exceeding the speci cations below may result in permanent damage to the device or device malfunction. operation outside of the parameters speci ed in the electrical characteristics section is not implied. exposure to absolute maximum rated conditions for extended periods of time may affect device reliability. parameter symbol conditions min typ max units supply voltage v in 4.5 5 5.5 v quiescent current i q v in = 5v 130 200 a standby current i q(off) en low 0.1 1.0 a input under-voltage lockout start threshold v uvlo v in rising 4.20 v hysteresis v hyst v in falling 0.10 v en enable input threshold v ih output on 2.8 v v il output off 1.8 enable input bias current v in = v en = 5v -1 +1 a
3 ? 2006 semtech corp. www.semtech.com SC339 power management parameter symbol conditions min typ max units adj adjust input bias current i adj v adj = 0.5v -100 0 +100 na reference voltage v adj 0c t a +85c -1% 0.500 1% v drv output current i drv sourcing 5 20 ma sinking 5 20 ma output voltage v drv full on, i drv = 0ma, v in = 5v 4.70 4.85 v output under-voltage protection trip threshold (2) v th(uv) measured at adj pin 40 50 60 %v adj pgd power good threshold (3) v th(pgd) measured at adj pin -15 -12 -8 %v adj output logic low voltage v pgd v adj = 0.4v, i pgd = -1ma 0.4 v power good leakage current i pgd v adj = 0.5v, 0v v pgd v in -1 0 +1 a soft-start output rise time 10% vout to 90% vout, vout = 1.05v t r from en rising to 99% of v out 500 1000 2000 s electrical characteristics notes: 1) v pwr = input voltage to pass device drain (or source depending upon orientation of fet). 2) if v th(uv) is exceeded for longer than 1ms (nom.) the protection circuitry will shut down the output. 3) during start-up only, v th(pgd) is -6% (typical), then switches to -12% (typical).
4 ? 2006 semtech corp. www.semtech.com SC339 preliminary power management pin descriptions notes: 1) only available in tape and reel packaging. a reel contains 2500 devices. 2) v in = 5v 3) v adj is 1% over 0c t a +85c. 4) lead-free product. this product is fully weee and rohs compliant. pin con guration ordering information part number package SC339sktrt sot-23 6 pin SC339evb evaluation board pin pin name pin function 1 in 5v supply 2 gnd ground 3 en active high enable control - connect to in if not being used - do not allow to oat 4 pgd power good signal output for v out 5 adj regulator sense input - used for sensing the output voltage for power good and under-voltage and to set the output voltage 6 drv output of regulator - drives the gate of an n-channel mosfet to maintain v out set by r1 and r2 marking information 1 4 5 6 3 2 drv in en pgd gnd adj top view (sot-23 6l) marking for sot23, 6 lead package: yyww = datecode (example: e652)
5 ? 2006 semtech corp. www.semtech.com SC339 power management block diagram shutdown control under voltage control + - + + - - vref 0.5 vbg 0.88 vbg (0.95 vbg at start-up) power good comparator vref ( 0.5v) en drv pgd in adj 0.5v bandgap reference undervoltage comparator error amplifier gnd
6 ? 2006 semtech corp. www.semtech.com SC339 preliminary power management applications information theory of operation the SC339 linear fet controller provides a simple way to drive an n-channel mosfet to produce tightly regulated output voltages from an available, higher, supply voltage. it takes its power from the 5v system supply, drawing 130 a (typ) while operating. it contains an internal bandgap reference which is compared to the output voltage via a resistor divider. the resistor divider is external and user selectable. the drive pin (drv) can pull up to a guaranteed minimum of 4.7v. thus, the device can be used to regulate a large range of output voltages by careful selection of the external mosfets (s ee component selection on this page) . the SC339 includes an active high enable control (en). if this pin is pulled low, the drive pin is pulled low, turning off the n-channel mosfet. if the pin is pulled up to 2.8v v en v in , the drive pin is enabled. this pin should not be allowed to oat. the SC339 has a power good output (pgd) which is an open drain output that pulls low if the related output is below the power good threshold (-12% of the programmed output voltage typical). the power good circuitry is active if the device is enabled, regardless of the state of the over-current latch. an over-current protection circuit monitors the output voltage. if the output voltage drops below 50% (typical) of nominal, as would occur during an over-current or short condition, the device will pull the drive pin low and latch off. toggle the power supply or enable pin to reset the latch condition. drive output the drive output is source and sink capable. the drivers both source and sink 20ma of current typically at 5v in. soft-start and power good timing at start-up, the internal reference is switched from its normal 0.5vdc to a 1ms (typical) linear ramp. the output voltage tracks the ramp until 0.5v is reached. the pwrgd signal is held low until the output has been in regulation approximately 500 sec to allow the output voltage to stabilize. the power-up is very smooth and monotonic. ocp and power supply sequencing the SC339 has output under-voltage protection that looks at the output to see if it is: a) less than 50% (typi- cal) of its nominal value and, b) v drv for that output is within 350mv (typical) of maximum. if both of these criteria are met, there is a 1ms (typical) delay and then the output is shut down. this provides inherent immunity to uv shutdown at start-up (which may occur while the output capacitors are being charged). at start-up, it is necessary to ensure the power supplies and enable are sequenced correctly to avoid erroneous latch-off. for uv latch-off not to oc- cur at start-up due to sequencing issues, the volt- age supplied to the mosfet drain should be greater than the output under-voltage threshold when that output is enabled. this assumes that the drop through the pass mosfet is negligible. if not, then this drop needs to be taken into account also since: v out = v drain - (i out x r ds(on) ) if the supply to the SC339 in pin comes up before the supply to the mosfet drain, then that output should be enabled after the supply to the mosfet drain is applied - the power good signal for this rail would be ideal. if the power supply to the mosfet drain comes up before the power supply to the SC339 in pin, then the output can either be enabled with the supply to the in pin or afterwards. please note the following example: SC339 powered from 5v, the mosfet (v drain ) powered from 1.8v, set for 1.5v out . worst-case: under-voltage threshold is 60% (over temperature) of 1.5v, or 0.9v. the typical enable threshold is ~2.4v, see figure 1 on page 7. component selection output capacitors: low esr capacitors such as sanyo poscaps or panasonic sp-caps are recommended for bulk capacitance, with ceramic bypass capacitors for decoupling high frequency transients. ceramic output capacitors may be used; however, use of ceramic output capacitors requires compensation on the drv output.
7 ? 2006 semtech corp. www.semtech.com SC339 power management applications information (cont.) note: r ds(on) must be met at all temperatures and at the mini- mum v gs condition. setting the output voltage: the adjust pin connects directly to the inverting input of the error ampli er, and the output voltage is set using external resistors (please refer to the typical application circuit on page 1). using output 1 as an example, the output voltage can be calculated as follows: r1 v out = 0.5 ? ( 1 + ?? ) r2 the input bias current for the adjust pin is so low that it can be safely ignored. to avoid picking up noise, it is recommended that the total resistance of the feedback chain be less than 100k . with ceramic capacitors, a recommended divider current of >100 a is recommended to keep the fet conducting during light load conditions to improve transient response. SC339 supply comes up before mosfet drain supply mosfet drain supply comes up before SC339 supply 2.8v 2.7v power supply sequencing input capacitors: placement of low esr capacitors such as sanyo poscaps or panasonic sp-caps at the input to the mosfet (v drain ) will help to hold up the power supply during fast load changes, thus improving overall transient response. if v drain is located at the bulk capacitors for the upstream voltage regulator, additional capacitance may not be required. in this case a 0.1 f ceramic capacitor will suf ce. the 5v bias supply to the SC339 should be bypassed with a 0.1 f ceramic capacitor. mosfets: very low or low threshold n-channel mosfets are required. select fets rated for v gs of 2.7v or lower. for the device to work under all operating conditions, a maximum r ds(on) must be met to ensure that the output will never go into dropout: v in(min) D v out(max) r dson(max) = ??????? i out(max)
8 ? 2006 semtech corp. www.semtech.com SC339 preliminary power management table 1 lists recommended resistor values for some stan- dard output voltages. all resistors are 1%, 1/10w. the maximum output voltage that can be obtained from each output is determined by the input supply voltage and the r ds(on) and gate threshold voltage of the external mosfet. assuming that the mosfet gate threshold voltage is sufficiently low for the output voltage chosen and the worst-case drive voltage, v out(max) is given by: v out (max) = v drain(min) D i out(max) ? r dson(max) recommended resistor values for SC339 design example goal: 1.05v5% @ up to 2.5a from 1.2v5% and 5v5% solution 1: no passive droop total window for dc error, ripple and transient is 52.5mv. since this device is linear and assuming that it has been designed to not ever enter dropout, there is negligible ripple on the output. the dc error for this output is the sum of: v adj accuracy = 1% = 10.5mv feedback chain tolerance = 1% = 10.5mv load regulation = 0.25% = 2.6mv resistors per table 1 should be 11.0k (top) and 10.0k (bottom). v out (v) r1 or r3 (k ) r2 or r4 (k ) 1.05 11.0 10.0 1.2 14.0 10.0 1.5 20.0 10.0 2.5 45.3 11.3 3.3 63.4 11.3 applications information (cont.) total dc error = 2.25% = 23.6mv this leaves 2.75% = 28.875mv for the load transient esr spike, therefore: 28.875mv r esr(max) = ?????? = 11.55m 2.5a bulk capacitance required is given by: dl ? c bulk(min) = ??? = f dv where di is the maximum load current step, t is the maximum regulator response time and dv is the allowable voltage droop. therefore with di = 2.5a, t = 1 s, and dv = 28.875mv: 2.5 ? 1 ? 10 6 c bulk(min) = ???????? = 87 f 28.875 ? 10 3 so if we use 1% v out set resistors we would select 100 f, 12m poscap for output capacitance (which assumes that local ceramic bypass capacitors will absorb the balance of the (12 - 11.55)m esr requirement - otherwise 10m capacitors should be used). if we use 0.1% set resistors, then the total dc error becomes 1.35% = 15.75mv, leaving 3.65% = 38.33mv for the esr spike. in this case: 38.33mv r esr(max) = ???? = 15.33m and, 2.5a = 2.5 ? 1 ? 10 6 c bulk(min) ??????? = 65 f 38.33 ? 10 3 so for 0.1% resistors we could use 1 x 100 f, 15m poscap for output capacitance.
9 ? 2006 semtech corp. www.semtech.com SC339 power management this is a very severe example, since the output voltage is so low, therefore the allowable window is very small. see solution 2 for an alternate circuit. for higher output voltages the components required will be less stringent. the input capacitance needs to be large enough to stop the input supply from collapsing below -5% (i.e., the design minimum) during output load steps. if the input to the pass mosfet is not local to the supply bulk capacitance then additional bulk capacitance may be required. mosfet selection: since the input voltage to the SC339 is 5v5%, the minimum available gate drive is: v gs = (4.4 D 1.1025 ) = 3.3v so a mosfet rated for v gs = 2.7v will be required, with an r ds(on)(max) (over-temperature) given by: ( v in(min) D v out ) ( 1.14 D 1.05 ) r dson(max) = ?????? = ?????? = 36m i out(max) 2.5 mosfet selection so-8 footprint vgs rds-on imax fds6682 1.7v 9m 14a irf7456 1.5v 6.5m 16a 1206 footprint vgs rds-on imax si5406dc 0.6v 20m 9.5a nths5404 0.6v 25m 7.2a sot-23 footprint vgs rds-on imax irlms2002 1v 30m 5.2a fdn337n (when input is > 1.2v for 1.05v output) 0.7v 65m 2.2a solution 2: using passive droop passive droop allows us to use almost the full output tolerance window for transients, therefore making the output capacitor selection simpler and less expensive. the trade-offs are the cost of the droop resistor versus the reduction in output capacitor cost, and the reduction in headroom which impacts mosfet selection. the top of the feedback chain connects to the input side of r droop , and the output is set for 1.075v. thus at no load, v out will be 1.075v (or 1.05v + 2.4%) and at i out = 2.5a, v out will be 1.025v (or 1.05v - 2.4%). if 1% set resistors are used, the total dc error will be 2.25% = 24mv. thus, at no load, the minimum output voltage will be given by: v out(min_no_load) = 1.075 D 0.024 = 1.051v this leaves 53.5mv for transient response, giving: 53.5mv = 21.4m and, r esr(max) = ???? 2.5a 2.5 ? 1 ? 10 6 = 47 f c bulk(min) = ??????? 53.5 ?10 3 instead of 2 x 100 f, 12m capacitors, we can use 1 x 47 f, 15m capacitor. applications information (cont.) 1.075v 1.2v +/-5% in 1.05v @ 2.5a c1 0.1uf r1 11.0k c3 100uf, 25mohm poscap 4 5 6 r2 10.0k rdroop 20mohm q1 in gnd en drv adj pgd 1 3 2 u1 SC339
10 ? 2006 semtech corp. www.semtech.com SC339 preliminary power management applications information (cont.) using ceramic capacitors SC339 is capable of operation using an all-ceramic so- lution, needing only an external r-c compensation. the typical application schematic (r3, c3) from page 1 is re- produced here: 1.05 v @ 3a SC339 in drv adj pgd en gnd c1 c2 c4 5 v in 1.05v enable 1.05 v power good 1.2 v +/-5 % in irf7311 or similar v out = (1+r1/r2)*0.5 notes : (1 ) optional components to use with ceramic output capacitors c3 (1) r3 (1) r1 r2 () c2 typical applications circuit 100 1k 10k 100k 1meg 10meg -40 -20 20 40 60 0,0 gain (db) freq (hz) low frequency pole generated internally pin low frequency zero generated internally zin rout / cout pole, moves with the load current prout high frequency pole generated by esr and output capacitor ceramic capacitor operation with very low esr for the output capacitor . we get a three pole 1 zero system as shown above and is unstable without external compensation pcout -60 -90 -180 90 180 270 -270 phase phase (deg) typical frequency response without compensation and ceramic output capacitors: SC339 frequency response with ceramic output capacitors and no compensation from this response we see that the system is not stable as it has a phase margin of approximately 0 degrees. for stable operation we introduce a low frequency pole and a zero. the low frequency pole is used to roll off the gain quicker and the zero is used to increase the band- width of the system. the pole-zero location: 100 1k 10k 100k 1meg 10meg -40 -20 20 40 60 0,0 gain (db) freq (hz) pin + pcomp zin + zcomp prout ceramic capacitor operation with compensation on drv pin pcout -60 -90 -180 90 180 270 -270 phase phase (deg) SC339 frequency response with ceramic output capacitors and r-c compensation from the above gure we can see that the overall re- sponse of the system is stable with a decent phase margin it is important to select the external compensation zero to be between 1 khz and 5 khz for optimum bandwidth and phase margin. in this example we have selected zero at approximately 3 khz. the compensation values are calculated by the following empirical equation: we chose a low r3 compensation value to roll off gain. r3 = 100 . ? ? ? r3 ? c3 = 3khz
11 ? 2006 semtech corp. www.semtech.com SC339 power management applications information (cont.) now, we choose c3 = 470nf as the standard value. soft-start behavior at start-up, v out rst ramps linearly from ground at the rate of ~0.5v/ms (+/- 25%) for about 800us. the linear ramping is followed by a phase of smooth settling for about 700us at the end of which the output has fully settled (to better than 1%). the total start-up time of about 1.5ms is kept within 1ms - 2ms window, and this is regardless of the loading and of the external components connected to the device. SC339 start-up response c3 = ? ? ? r3 ? 3khz = 530nf layout guidelines the advantages of using the SC339 to drive external mosfets are: a) that the bandgap reference and control circuitry are in a die that does not contain high power dissipating devices and, b) that the device itself does not need to be located right next to the power devices. thus very accurate output voltages can be obtained since changes due to heating effects will be minimal. the 0.1 f bypass capacitor should be located close to the supply (in) and gnd pins, and connected directly to the ground plane. the feedback resistors should be located at the device, with the sense line from the output routed from the load (or top end of the droop resistor if passive droop is being used) directly to the feedback chain. if passive droop is being used, the droop resistor should be located next to the load to avoid adding additional unplanned droop. sense and drive lines should be routed away from noisy traces or components. for very low input to output voltage differentials, the input to output/load path should be as wide and short as possible. where greater headroom is available, wide traces may suf ce. power dissipation within the device is practically negligible, thus requiring no special consideration dur- ing layout. the mosfet pass devices should be laid out according to the manufacturer?s guidelines for the power being dissipated within them.
12 ? 2006 semtech corp. www.semtech.com SC339 preliminary power management performance characteristics supply current vs. supply voltage v cc = 4.5v to 5.5v, i out = 2.5a, v in = 1.5v, v en = 5v 125.0e-6 130.0e-6 135.0e-6 140.0e-6 145.0e-6 150.0e-6 155.0e-6 160.0e-6 4.500 4.600 4.700 4.800 4.900 5.000 5.100 5.200 5.300 5.400 5.500 v cc (v) i cc (a) supply current figure 1: supply current v/s supply voltage adjust voltage vs. output current i out = 0a to 3a, v in = 1.5v, v cc = 5.0v, v en = 5v 0.4940 0.4960 0.4980 0.5000 0.5020 0.5040 0.5060 0.000 0.500 1.000 1.500 2.000 2.500 3.000 i out (a) v adj (v) adjust voltage +1% -1% figure 2: adjust voltage v/s output current (1% accurate) figure 3: soft start waveform shows the pwrgd delay figure 4: input uvlo test (rising) figure 5: input uvlo test (falling) figure 6: enable threshold detect (rising)
13 ? 2006 semtech corp. www.semtech.com SC339 power management performance characteristics figure 7: enable threshold detect (falling) figure 8: transient load rising edge figure 9: transient load falling edge
14 ? 2006 semtech corp. www.semtech.com SC339 preliminary power management outline drawing - sot-23 6 .110 bsc .037 bsc detail aaa c seating ccc c 2x n/2 tips 2x e/2 6 see detail a1 a a2 bxn a .008 12 n e .060 .114 .063 .118 .010 - 6 a 0.20 1.60 3.00 2.80 bsc 0.95 bsc .069 1.50 2.90 .020 0.25 1.75 0.50 - ei l (l1) c 01 0.25 plane gage h 2.80 .110 bbb c a-b d 0 .008 - .004 .012 .003 (.024) .018 - .035 .000 .035 - - .045 0.10 0.20 10 0 - 10 1.15 (0.60) 0.45 .024 .009 0.30 0.08 .057 .051 .006 0.00 .90 0.90 0.22 0.60 - 0.15 1.45 1.30 - - 1.90 bsc .075 bsc a e1 d e b c h nom inches dimensions l1 aaa bbb ccc 01 n dim c e e1 l e1 e d a1 a2 b a min millimeters max min nom max plane d datums and to be determined at datum plane controlling dimensions are in mi llimeters (angles in degrees). dimensions "e1" and "d" do no t include mold flash, protrusions 3. or gate burrs. notes: 1. 2. -a- -b- -h- side view
15 ? 2006 semtech corp. www.semtech.com SC339 power management this land pattern is for re ference purposes only. consult your manufacturin g group to ensure your company's manufacturing guidelines are met. notes: 1. dimensions inches y z dim g p x c millimeters p (c) z y g .043 .141 .055 (.098) .037 .024 1.40 (2.50) 0.95 0.60 1.10 3.60 x dimensions inches y z dim g p x c millimeters land pattern - sot-23 6 semtech corporation power management products division 200 flynn road, camarillo, ca 93012 phone: (805) 498-2111 fax: (805) 498-3804 contact information www.semtech.com

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