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1 www.semtech.com SC194A 1a synchronous buck converter with integrated power devices power management july 05, 2006 typical application circuit applications the SC194A is a synchronous step-down converter with integrated power devices. the SC194A is designed for single-cell li-ion battery applications, but can also be used in xed 3.3v or 5v applications. the switching frequency is nominally set to 1mhz, allowing the use of small inductors and capacitors. the 1.3a maximum current rating of the internal mosfet switches allows a dc output current of 1a. the SC194A has a exible clocking methodology that allows it to be synchronized to an external oscillator or controlled by the internal oscillator. the device can operate in either forced pwm mode or in psave mode. if psave mode is enabled the part will automatically enter pfm at light loads to maintain maximum ef ciency across the full load range. for noise sensitive applications, psave mode can be disabled by synchronizing to an external oscillator, or pulling the sync/pwm pin high. shutdown turns off all the control circuitry to achieve a typical shutdown current of 0.1 a. cell phones wireless communication chipset power personal media player notebook and sub-notebook computers pdas and mobile communicators wlan peripherals ? ? ? ? ? ? up to 93% ef ciency output current - 1a input range - 2.7v to 5.5v quiescent current - 17 a four selectable output voltages dynamic voltage positioning capability fixed 1mhz frequency or 750khz to 1.25mhz synchronized operation psave operation to maximize ef ciency at light loads minimal external components fast transient response 100% duty cycle in dropout soft-start over-temperature and short-circuit protection space-saving lead-free package - mlp-10, 3 x 3mm ? ? ? ? ? ? ? ? ? ? ? ? ? ? description features SC194A vin lx en sync/pwm vout vid0 vid1 pgnd mode gnd c in l1 c out 10 f 10 f 4.7 h v in 2.7v to 5.5v v out 1.8v 1a
2 ? 2006 semtech corp. www.semtech.com SC194A preliminary power management electrical characteristics unless otherwise noted: v in = 3.6v, en = v in , sync/pwm = v in , mode = v in , t a = -40 to 85c. typical values are at t a = 25c. parameter symbol conditions min typ max units input voltage range v in 2.7 5.5 v vout accuracy v out i out = 0.5a, t a = 25c 1 % vout temperature accuracy v out(t) i out = 0.5a, t a = -40 to 85c 0.3 0.7 % line regulation v out line v in = 2.7v to 5.5v, v out = 1.8v, i out = 0.5a, t a = -40 to 85c 0.4 0.65 % load regulation (pwm) v out load i out = 0a to 1a, t a = -40 to 85c 0.3 0.65 % psave regulation v out psave sync/pwm =gnd, c out =22 f +1.3 -0.3 +1.6 -0.6 % p-channel on resistance r dsp i lx = 100ma 0.275 n-channel on resistance r dsn i lx = 100ma 0.165 start-up time t start 5ms p-channel current limit i lim(p) 1.33 1.9 2.47 a 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 recommended. parameter symbol maximum units input supply voltage v in -0.3 to 7 v logic inputs (sync/pwm, en, mode, vid0, vid1) v n -0.3 to v in +0.3, 7v max v output voltage v out -0.3 to v in +0.3, 7v max v lx voltage v lx -1 to v in +1, 7v max v thermal impedance junction to ambient (1) ja 40 c/w vout short-circuit to gnd t sc continuous s operating ambient temperature range t a -40 to +85 c storage temperature t s -60 to +160 c junction temperature t jc -40 to +150 c peak ir re ow temperature t lead 260 c esd protection level (2) v esd 2kv absolute maximum ratings note: 1) calculated from package in still air, mounted to 3? x 4.5?, 4 layer fr4 pcb with thermal vias under the exposed pad per jesd 51 standards. 2) tested according to jedec standard jesd22-a114-b.
3 ? 2006 semtech corp. www.semtech.com SC194A preliminary power management electrical characteristics (cont.) parameter symbol conditions min typ max units quiescent current i q sync/pwm = gnd, i out = 0a, v out = 1.04 x v out(programmed) 17 28 a shutdown current i sd en = gnd, lx = open 0.1 1 a lx leakage current pmos i lxp lx = gnd, en = gnd 0.1 2 a lx leakage current nmos i lxn lx = 3.6v, en = gnd -2 0.1 a oscillator frequency f osc 0.85 1.0 1.15 mhz sync frequency (upper) f syncu 1.25 mhz sync frequency (lower) f syncl 750 khz uvlo threshold (upper) v uvl 2.38 2.52 2.65 v uvlo hysteresis v uvlhys 50 mv thermal shutdown t sd 145 c thermal shutdown hysteresis t sd-hys 10 c logic input high v ih en, sync/pwm, vid0, vid1, mode 1.6 v logic input low v il en, sync/pwm, vid0, vid1, mode 0.6 v logic input current high i ih en, sync/pwm, vid0, vid1, mode -2 0.1 2 a logic input current low i il en, sync/pwm, vid0, vid1, mode -2 0.1 2 a
4 ? 2006 semtech corp. www.semtech.com SC194A preliminary power management pin con guration ordering information programmable output voltage notes: 1) lead-free packaging only. this product is fully weee and rohs compliant. 2) available in tape and reel only. a reel contains 3000 devices. vid1 vid0 SC194A v out 0 0 1.0v 0 1 1.2v 1 0 1.5v 1 1 1.8v device package SC194Amltrt (1)(2) mlp 3x3-10 SC194Aevb evaluation board ordering information marking information top view 1 2 3 4 10 9 8 7 56 mlp10: 3x3 10 lead vin mode sync/ pwm en vout lx pgnd gnd vid1 vid0 t
5 ? 2006 semtech corp. www.semtech.com SC194A preliminary power management block diagram control logic plimit amp current amp nlimit amp osc & slope generator pwm comp error amp 500mv ref mode vid1 vid0 vout sync /pwm en gnd pgnd lx vin voltage select 8 9 10 1 6 5 7 2 3 4 psave comp
6 ? 2006 semtech corp. www.semtech.com SC194A preliminary power management pin descriptions pin # pin name pin function 1 vin input power supply voltage 2 mode mode select pin - mode = v in to select 100% duty cycle function, mode = gnd to disable 3 sync/pwm oscillator synchronization input - tie to v in for forced pwm mode or gnd to allow the part to enter psave mode at light loads. apply an external clock signal for frequency synchronization. 4en enable digital input - a high input enables the SC194A, a low disables and reduces quiescent current to less than 1 a. in shutdown, lx becomes high impedance. 5 vout regulated output voltage and feedback for SC194A 6 vid0 logic level bit 0 used in conjunction with vid1 to set the output voltage. connect high or low as required to select the desired output voltage. if not connected, the output voltage will be indeterminate. 7 vid1 logic level bit 1 used in conjunction with vid0 to set the output voltage. connect high or low as required to select the desired output voltage. if not connected, the output voltage will be indeterminate. 8 gnd ground 9 pgnd power ground 10 lx inductor connection to the switching fets t thermal pad pad for heatsinking purposes - not connected internally. connects to ground plane using multiple vias.
7 ? 2006 semtech corp. www.semtech.com SC194A preliminary power management applications information SC194A detailed description the SC194A is a synchronous step-down pulse width modulated (pwm), dc-dc converter utilizing a 1mhz xed-frequency current mode architecture. the device is designed to operate in a xed-frequency pwm mode across the full load range and can enter power save mode (psave) utilizing pulse frequency modulation (pfm) at light loads to maximize ef ciency. operation during normal operation the pmos mosfet is activated on each rising edge of the internal oscillator. current feedback for the switching regulator uses the pmos current path, and it is ampli ed and summed with the internal slope compensation network. the voltage feedback loop uses an internal feedback divider. the on- time is determined by comparing the summed current feedback and the output of the error ampli er. the period is set by the onboard oscillator or by an external clock attached to the sync/pwm pin. the SC194A has an internal synchronous nmos recti er and does not require a schottky diode on the lx pin. programmable output voltage the SC194A has four pre-determined output voltage values which can be individually selected by the correct programming of the vid0 and vid1 pins (see programmable output voltage table on page 4). this eliminates the need for external programming resistors saving pcb area and inventory. the vid pins can be statically tied to gnd or vin for xed output con gurations or they may be driven by a microprocessor enabling the possibility of dynamic voltage adjustment for host equipment "sleep" states. continuous conduction & oscillator synchronization the SC194A is designed to operate in continuous conduction, xed-frequency mode. when the sync/ pwm pin is tied high the part runs in pwm mode using the internal oscillator. the part can be synchronized to an external clock by driving a clock signal into the sync/ pwm pin. the part synchronizes to the rising edge of the clock. protection features the SC194A provides the following protection features: ? thermal shutdown ? current limit ? over-voltage protection ? soft-start thermal shutdown the device has a thermal shutdown feature to protect the SC194A if the junction temperature exceeds 145c. in thermal shutdown the on-chip power devices are disabled, tri-stating the lx output. switching will resume when the temperature drops by 10c. during this time if the output voltage decreases by more than 60% of its programmed value, a soft-start will be invoked. current limit the pmos and nmos power devices of the buck switcher stage are protected by current limit functions. in the case of a short to ground on the output, the part enters frequency foldback mode, that causes the switching frequency to divide by a factor determined by the output voltage. this prevents the inductor current from "stair- casing". over-voltage protection over-voltage protection is provided on the SC194A. in the event of an over-voltage on the output in switcher mode, the pwm drive is disabled, tri-stating the lx output. the part will not resume switching until the output voltage has fallen below 2% of the regulation voltage. soft-start the soft-start mode is enabled after every shutdown cycle to limit in-rush current. in conjunction with the frequency foldback, this controls the maximum current during start- up. the pmos current limit is stepped up through seven soft-start levels to the full value by a timer driven from the internal oscillator. during soft-start, the switching frequency is stepped by 1/8, 1/4, and 1/2 of the internal oscillator frequency up to the full value, under control of three output voltage thresholds. as soon as the output voltage is within 2% of the regulation voltage, soft-start mode is disabled. power save mode operation the psave mode may be selected by tying the sync/pwm pin to gnd. selecting psave mode will enable the SC194A to automatically activate/deactivate operation at light loads maximizing ef ciency across the full load range. the SC194A automatically detects the load current at which it should enter psave mode. the SC194A is optimized to track maximum ef ciency with respect to v in .
8 ? 2006 semtech corp. www.semtech.com SC194A preliminary power management applications information (cont.) in psave mode v out is driven from a lower level to an upper level by a switching burst. once the upper level has been reached the switching is stopped and the quiescent current is reduced. v out falls from the upper to lower levels in this low current state as the load current discharges the output capacitor. the burst-to-off period in psave will decrease as the load current reduces. the psave switching burst frequency is controlled so that the inductor current ripple is similar to that in pwm mode. the minimum switching frequency during this period is limited to 650khz. the SC194A automatically detects when to exit psave mode by monitoring v out . for the SC194A to exit psave mode, the load must be increased, causing v out to decrease until the power save exit threshold is reached. psave levels are set high to minimize the undershoot when exiting psave. the lower psave comparator level is set +0.7% above v out , and the upper comparator level at +1.5% above v out , with the exit threshold at -2% below v out . if psave operation is required then a 22 f output capacitor must be used. 100% duty cycle operation the 100% duty cycle mode may be selected by connecting the mode pin high. this will allow the SC194A to maintain output regulation under low input voltage/high output voltage conditions. in 100% duty cycle operation, as the input supply drops toward the output voltage, the pmos on-time increases linearly above the maximum value in xed-frequency operation until the pmos is active continuously. once the pmos is switched on continuously, the output voltage tracks the input voltage minus the voltage drop across the pmos power device and inductor according to the following relationship: where, v out = output voltage v in = input voltage i out = output current r dsp = pmos switch on resistance r ind = series resistance of the inductor the 100% duty cycle can only operate for a programmed output voltage of 1.8v. with an output voltage of 1.8v, 100% duty cycle mode will only be required to maintain regulation if v in falls below a minimum value shown in the graph below. ) r r ( i v v ind dsp out n i out + ? = ) r r ( i v v ind dsp out n i out + ? = minimum v in for fixed frequency operation vs. r ind power save operation 2.7 2.75 2.8 2.85 2.9 2.95 3 0.05 0.1 0.15 0.2 0.25 0.3 v in (v) inductor dc resistance ( ) v out = 1.8v i out =1a v out 0.7% 1.5% psave mode at light load pwm mode at medium/ high load -2% burst off higher load applied 0 a inductor current time
9 ? 2006 semtech corp. www.semtech.com SC194A preliminary power management output voltage ripple is a combination of the voltage ripple from the inductor current charging and discharging the output capacitor and the voltage created from the inductor current ripple through the output capacitor esr. selecting an output capacitor with a low esr will reduce the output voltage ripple component, as can be seen in the following equation: v out(esr) = i l(ripple) esr cout capacitors with x7r or x5r ceramic dielectric are strongly recommended for their low esr and superior temperature and voltage characteristics. y5v capacitors should not be used as their temperature coef cients make them unsuitable for this application. table 2 lists the manufacturers of recommended capacitor options. table 1: recommended inductors manufacturer/part # value h dcr saturation current a tolerance % dimensions (lxwxh) mm bi technologies hm66304r7 4.7 0.072 1.32 20 4.7 4.7 3.0 coilcraft d01608c-472ml 4.7 0.09 1.5 20 6.6 4.5 3.0 tdk vlcf4018t- 4r7n1r0-2 4.7 0.101 1.07 30 4.3 4.0 1.8 table 2: recommended capacitors manufacturer/part # value f rated voltage vdc temperature characteristic case size murata grm21br60j226me39l 22 6.3 x5r 0805 murata grm188r60j106 mke19 10 6.3 x5r 0603 tdk c2012x5r0j106k 10 6.3 x5r 0603 note: where psave operation is required 22 f must be used for c out . applications information (cont.) the SC194A is designed for use with a 4.7 h inductor. the magnitude of the inductor current ripple is dependent on the inductor value and can be determined by the following equation: v out v out i l = ??? ( 1 - ??? ) l f osc v in this equation demonstrates the relationship between input voltage, output voltage, and inductor ripple current. the inductor should have a low dcr to minimize the conduction losses and maximize ef ciency. as a minimum requirement, the dc current rating of the inductor should be equal to the maximum load current plus half of the inductor current ripple as shown by the following equation: i l i l(pk) = i out(max) + ?? 2 final inductor selection will depend on various design considerations such as ef ciency, emi, size and cost. table 1 lists the manufacturers of practical inductor options. c in selection the source input current to a buck converter is non- continuous. to prevent large input voltage ripple a low esr ceramic capacitor is required. a minimum value of 10 f should be used for suf cient input voltage ltering and a 22 f should be used for improved input voltage ltering. c out selection the internal compensation is designed to work with a certain output lter corner frequency de ned by the equation: this single pole lter is designed to operate with a minimum output capacitor value of 10 f. larger output capacitor values will improve transient performance. if psave operation is required the minimum capacitor value is 22 f. f c = 1 2 l c out
10 ? 2006 semtech corp. www.semtech.com SC194A preliminary power management pcb layout considerations poor layout can degrade the performance of the dc-dc converter and can contribute to emi problems, ground bounce and resistive voltage losses. poor regulation and instability can result. a few simple design rules can be implemented to ensure good layout: place the inductor and lter capacitors as close to the device as possible and use short wide traces between the power components. 1. applications information (cont.) route the output voltage feedback path away from the inductor and lx node to minimize noise and magnetic interference. maximize ground metal on the component side to improve the return connection and thermal dissipation. separation between the lx node and gnd should be maintained to avoid coupling of switching noise to the ground plane. use a ground plane with several vias connecting to the component side ground to further reduce noise interference on sensitive circuit nodes. 2. 3. 4.
11 ? 2006 semtech corp. www.semtech.com SC194A preliminary power management ef ciency vs. load current v out = 1.0v typical characteristics ef ciency vs. load current v out = 1.5v ef ciency vs. load current v out = 1.2v ef ciency vs. load current v out = 1.8v pwm to psave hysteresis 70 75 80 85 90 95 0.001 0.01 0.1 1 psave entry for decreasing i out psave mode i out decreasing psave mode i out increasing psave exit for increasing i out pwm mode efficiency (%) i out (a) 0 10 20 30 40 50 60 70 80 90 100 0.0001 0.001 0.01 0.1 1 i out (a) efficiency (%) v in =3.6v psave v in =4.2v psave v in =2.7v psave v in =3.6v pwm v in =4.2v pwm v in =2.7v pwm 0 10 20 30 40 50 60 70 80 90 100 0.0001 0.001 0.01 0.1 1 v in =3.6v psave v in =4.2v psave v in =2.7v psave efficiency (%) i out (a) v in =3.6v pwm v in =4.2v pwm v in =2.7v pwm 0 10 20 30 40 50 60 70 80 90 100 0.0001 0.001 0.01 0.1 1 v in =3.6v psave v in =4.2v psave v in =2.7v psave v in =3.6v pwm v in =4.2v pwm v in =2.7v pwm i out (a) efficiency (%) 0 10 20 30 40 50 60 70 80 90 100 0.0001 0.001 0.01 0.1 1 v in =3.6v pwm v in =4.2v pwm v in =2.7v pwm v in =3.6v psave v in =4.2v psave v in =2.7v psave efficiency (%) i out (a) 70 75 80 85 90 95 100 2.5 3.0 3.5 4.0 4.5 5.0 5.5 vin(v) eff(%) v out =1.8v,pwm v out =1.8v,psave v out =1v,pwm v out t=1v,psave ef ciency vs. input voltage i out =500 ma(pwm)/50 ma(psave)
12 ? 2006 semtech corp. www.semtech.com SC194A preliminary power management typical characteristics (cont.) v out vs. i out , v out =1.8v, pwm v out vs. temperature v out =1.8v, pwm 1.7975 1.7980 1.7985 1.7990 1.7995 1.8000 1.8005 1.8010 1.8015 1.8020 1.8025 0 0.2 0.4 0.6 0.8 11.2 i out (a) v out (v) quiescent current vs. input voltage quiescent current vs. input voltage p-channel r dson vs. input voltage 1.8040 1.8045 1.8050 1.8055 1.8060 1.8065 1.8070 1.8075 1.8080 1.8085 1.8090 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 t a ( c) vout(v) 12 13 14 15 16 17 18 19 20 21 22 2.5 3 3.5 4 4.5 5 5.5 6 quiescent current ( a) v in (v) t a = 85 c t a = 25 c t a = 40 c psave mode 3 3.5 4 4.5 5 5.5 6 2.5 3 3.5 4 4.5 5 5.5 6 v in (v) quiescent current (m a) t a = 85 c t a = 25 c t a = -40 c pwm mode 0.10 0.15 0.20 0.25 0.30 0.35 0.40 2.7 3.2 3.7 4.2 4.7 5.2 t a = 85 c t a = 25 c t a = -40 c v in (v) r dson ( ) v out (v) v in (v) 1.80 1.81 1.82 1.83 1.84 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 v out =1.8v pwm i out =500ma v out =1.8v psave i out =50ma v out vs. v in
13 ? 2006 semtech corp. www.semtech.com SC194A preliminary power management typical characteristics (cont.) 100% duty cycle mode psave operation pwm operation n-channel r dson vs. input voltage switching frequency vs. temperature psave start up 0.10 0.12 0.14 0.16 0.18 0.20 0.22 2.7 3.2 3.7 4.2 4.7 5.2 t a = 85 c t a = 25 c t a = -40 c v in (v) r dson ( ) 950 960 970 980 990 1000 1010 1020 1030 1040 1050 -50 -30 -10 10 30 50 70 90 110 130 v in = 5.5v t j = ( c) switching frequency (khz ) v in = 3.6v v in = 2.7v time (400ns/div) condition v in =2.6v, v out =1.8v, l out =1.4a, sync/pwm=1.15mhz ext clock v out (50mv/div) i load (1a/div) v lx (2v/div) time (1us/div) condition v in =3.6v, v out =1.8v, l out =150ma, sync/pwm=gnd v out (20mv/div) i l (200ma/div) v lx (5v/div) time (1us/div) condition v in =3.6v, v out =1.8v, l out =150ma, sync/pwm=v in v out (10mv/div) i l (200ma/div) v lx (5v/div) en (2v/div) v out (1v/div) l in (100ma/div) time (200us/div) condition v in =3.6v, v out =1.8v, l out =10ma, sync/pwm=gnd
14 ? 2006 semtech corp. www.semtech.com SC194A preliminary power management pwm start-up typical characteristics (cont.) load transient response pwm load transient response psave vid code change en (2v/div) v out (1v/div) l in (100ma/div) time (200us/div) condition v in =3.6v, v out =1.8v, l out =10ma, sync/pwm=v in v out (100mv/div) i load (1a/div) time (100us/div) condition v in =3.6v, v out =1.8v, l out =1a to 100ma, sync/pwm=v in vid0 (2v/div) v out (200mv/div) time (400us/div) condition v in =3.6v, v out =1.8v to 1.5v, l out =1a, sync/pwm=v in time (100us/div) condition v in =3.6v, v out =1.8v, l out =1a to 100 ma, sync/pwm=gnd v out (100mv/div) i load (1a/div)
15 ? 2006 semtech corp. www.semtech.com SC194A preliminary power management SC194A vin lx en sync/pwm vout vid0 vid1 pgnd mode gnd c in l1 c out 10 f 10 f 4.7 h v in 2.7v to 5.5v v out 1v 1a applications circuits v out = 1.8v with psave and 100% duty cycle v out = 1.0v with forced pwm and no 100% duty cycle SC194A vin lx en sync/pwm vout vid0 vid1 pgnd mode gnd c in l1 c out 22 f 10 f 4.7 h v in 2.7v to 5.5v v out 1.8v 1a SC194A vin lx en sync/pwm vout vid0 vid1 pgnd mode gnd l1 c out 22 f 4.7 h v in 2.7v to 5.5v c in 10 f ?sleep? flag from uproc changes voltage from 1.8v to 1.2v v out 1.8v norm v out 1.2v ?sleep? mobile voltage positioning for reduced system dissipation in "sleep" modes
16 ? 2006 semtech corp. www.semtech.com SC194A preliminary power management outline drawing - mlp-10 min aaa bbb b e l n d c e a1 a2 a dim millimeters nom dimensions max nom inches min max .114 .118 .122 2.90 3.00 3.10 - - - - (laser mark) indicator pin 1 1 n 2 notes: controlling dimensions are in mi llimeters (angles in degrees). coplanarity applies to the ex posed pad as we ll as terminals. 2. 1. .003 .007 .042 10 .009 .048 - .000 .031 (.008) 0.08 0.23 10 .011 .052 0.18 1.06 .039 - .002 - 0.00 0.80 1.31 0.30 1.21 - 0.05 1.00 (0.20) .004 0.10 0.50 bsc .020 bsc 0.30 .012 .020 .016 0.40 0.50 a aaa c a2 seating plane a1 a bxn bbb c a b b e c c d lxn e e .074 .079 .083 1.87 2.02 2.12
17 ? 2006 semtech corp. www.semtech.com SC194A preliminary power management land pattern - mlp-10 .087 .055 2.20 1.40 .150 .020 .012 .037 3.80 0.30 0.95 0.50 (.112) .075 1.90 (2.85) k h x this land pattern is for reference purposes only. consult your manufacturing group to ensure your company's manufacturing guidelines are met. notes: 1. inches dimensions g k h x y p z c dim millimeters y z g (c) p 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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