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description october 19, 2006 typical application circuit the SC198 is a high-ef ciency, dual synchronous buck converter designed for use in low power applications. each converter is capable of supplying up to 600ma of average current at one of eight programmable output voltages commonly used as microprocessor supply voltages. the SC198 uses a single control logic block for the two converters, but their controls can be set independently. the SC198 employs a exible clocking scheme that allows the user to use the xed internal 1mhz oscillator or synchronize the clock to an external source. the device also has an optional power-save mode that optimizes ef ciency for light loads. the SC198 provides output voltage exibility while conserving board space by using control pins to select the output voltage instead of external resistor voltage divider circuits. this eliminates at least four parts from the traditional dual buck converter bill of materials. dual buck converters with independent control high ef ciency - over 90% peak 8 programmable output voltages input voltage range between 2.7v to 5.5v fixed-frequency operation - 1mhz optional sync clock input optional power-save under light-load conditions shutdown current <1 a soft-start to limit in-rush current 4mm x 4mm mlpq package features applications 4.7 h 4.7 h vina vinr vinb ena ctla0 ctla1 ctla2 enb ctlb0 ctlb1 ctlb2 lxa vouta gnda lxb voutb gndb sync gndr voutb 1 18 15 5 6 7 16 11 10 9 17 2 4 3 14 12 13 8 20 10 f 10 f vouta 10 f SC198 mobile phones cordless phones mp3 players digital cameras pdas single li-ion cell or (3) nimh/nicd cell devices digital multimedia broadcast (dmb) devices portable gaming systems www.semtech.com 1 SC198 dual dc-dc buck converter with high current capability power management
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. unless otherwise noted: v in = 3.6v, sync = v in , l = 4.7 h, c = 10 f, t a = -40c 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 (1) ? v out i out = 10ma to 600ma -3 3 % line regulation v linereg v in = 2.7 to 5.5v, v out = 1.8v, i out = 300ma 0.2 %/v load regulation v loadreg i out = 10ma to 600ma 0.0008 %/ma minimum duty cycle dc min 18 % lxa, lxb current limit i lim 0.9 a quiescent current i q i out = 0ma, sync = 0, ena, enb = v in 50 a shutdown current i sd ena, enb = 0, lxa, lxb = open 0.1 1 a lxa and lxb leakage current i lxa , i lxb v in = 5.5v, lx = 0v, pmos 0.1 1 a v in = 5.5v, lx = v in , nmos -2 0.1 a p-channel on resistance r dsp i lxa , i lxb = 100ma 0.35 n-channel on resistance r dsn i lxa , i lxb = 100ma 0.25 absolute maximum ratings electrical characteristics parameter symbol maximum units vin v in -0.3 to 7 v en, sync input v en , v sync -0.3 to v in +0.3 v lxa and lxb voltages v lxa , v lxb -1 to v in +1 v vout v out -0.3 to v in +0.3 v ctla0, ctla1, ctla2, ctlb0, ctlb1 & ctlb2 voltages -0.3 to v in +0.3 v output short circuit to gnd t sc inde nite s lxa and lxb currents i lxa and i lxb 1.2 a thermal impedance (junction to ambient) (1) ja 40 oc/w operating ambient temperature t a -40 to +85 oc maximum junction temperature t j 150 oc storage temperature t s -65 to +150 oc re ow solder temperature t pkg 260 c esd protection level (2) v esd 2kv 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 as per jesd51 standards. (2) tested according to jedec standard jesd22-a114-b. 2 ? 2006 semtech corp. www.semtech.com SC198 power management
electrical characteristics (cont.) parameter symbol conditions min typ max units start-up time t start 5 ms oscillator frequency f osc 0.85 1.1 1.25 mhz sync frequency (upper) f syncu 1.25 mhz sync frequency (lower) f syncl 0.75 mhz thermal shutdown t hi 145 c thermal shutdown hysteresis t hysr 10 c uvlo threshold v uvl decreasing v in 2.4 2.5 2.6 v uvlo hysteresis v uvlhys 50 mv logic input high (2) v ih 1.6 v logic input low (2) v il 0.6 v logic input high (2) i ih -2 0.1 2 a logic input low (2) i il -2 0.1 2 a notes : (1) see output voltage options table in the application information section. (2) for ena, enb, sync, ctla0, ctla1, ctla2, ctlb0, ctlb1, ctlb2. 3 ? 2006 semtech corp. www.semtech.com SC198 power management
electrical characteristics (cont.) pin con guration device package (1) SC198mltrt (2)(1) (1)(2) mlpq-20 SC198evb evaluation board ordering information notes: (1) available in tape and reel only. a reel contains 3,000 devices. (2) available in lead-free package only. device is weee and rohs compliant. marking information SC198 yyww xxxxx xxxxx yy = two digit year of manufacture ww = two digit week of manufacture xxxxx = lot number top view 1 2 3 4 12 11 10 9 16 15 14 13 5 678 mlpq20: 4x4 20 lead 17 18 19 20 t vina lxa gnda vouta ctla0 vinb lxb gndb voutb ctlb0 ena nc vinr sync enb ctla1 ctla2 gndr ctlb2 ctlb1 4 ? 2006 semtech corp. www.semtech.com SC198 power management
pin # pin name pin function 1 vina input power supply voltage converter a 2 lxa connection point for the inductor on converter a 3 gnda ground reference to converter a 4 vouta feedback control input for converter a 5 ctla0 voltage select control pin 0 for output a (see table a ? output voltage options). (1) 6 ctla1 voltage select control pin 1 for output a (see table a ? output voltage options). (1) 7 ctla2 voltage select control pin 2 for output a (see table a ? output voltage options). (1) 8 gndr ground for reference supply 9 ctlb2 voltage select control pin 2 for output b (see table a ? output voltage options). (1) 10 ctlb1 voltage select control pin 1 for output b (see table a ? output voltage options). (1) 11 ctlb0 voltage select control pin 0 for output b (see table a ? output voltage options). (1) 12 voutb feedback control input for converter b 13 gndb ground reference for converter b 14 lxb connection point for the inductor on converter b 15 vinb input power supply voltage for converter b 16 enb enable pin for output b 17 sync oscillator synchronization input - connect to vin for forced pwm mode, ground for power-save mode or connect to an external clock for frequency synchronization. 18 vinr reference supply input 19 nc not connected 20 ena enable pin for output a t thermal pad thermal pad for heatsinking purposes ? connect to ground plane using multiple vias ? not connected internally pin descriptions note: (1) all ctl pins must be pulled high or low for proper operation. 5 ? 2006 semtech corp. www.semtech.com SC198 power management
block diagram current amp vinb lxb gndb p limit amp switching control logic n limit amp oscillator and slope generator error amp a voltage select error amp b voutb voltage select ctlb0 ctlb1 ctlb2 error amp a error amp b current amp p limit amp pwm comp pwm comp n limit amp vina lxa gnda vouta ctla0 ctla1 ctla2 sync voltage references vref3 vref3 vref2 vref2 vref1 vref1 vref1 vref2 vref3 gndr ena enb vinr 6 ? 2006 semtech corp. www.semtech.com SC198 power management
applications information 7 ? 2006 semtech corp. www.semtech.com SC198 power management SC198 detailed description the SC198 is a dual step-down, pulse-width modulated dc-dc converter with programmable output voltage and power-save mode. this device has a 1mhz internal oscillator that can be used during forced pwm mode or power-save mode (psave). operation during normal operation, the pmos switch is activated on each rising edge of the internal oscillator. current feedback for the switching regulator is through 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. when synchronizing to an external frequency, the SC198 operates in pwm mode only. the device has an internal synchronous nmos recti er and does not require a schottky diode on the lx pin. the device is designed to operate as a buck converter in pwm mode with a xed frequency of 1mhz. at light loads the part can enter psave mode to maximize ef ciency. output filter the SC198 converter also has internal loop compensa- tion. the internal compensation is designed to work with a certain output lter corner frequency de ned by the equation: 1 f c = ????? 2 lc ??? when selecting output lter components, the lc product should not vary over a wide range. selection of smaller inductor and capacitor values will move the corner fre- quency, potentially impacting system stability. due to this issue the practical lower limit for the inductor value is 4.7 h. the internal compensation is designed to oper- ate with a single-pole output lter, l = 4.7 h and c out = 10 f. programmable output voltage the SC198 has three control pins per output to allow the user to select a voltage level from eight predetermined output voltage levels (see table a, output voltage options below). the output voltage can be selected at any time, including while the output is enabled and loaded. table a ? output voltage options programmable output voltage ctla2/b2 ctla1/b1 ctla0/b0 nominal output voltage (v) 000 1 0 0 1 1.2 0 1 0 1.375 0 1 1 1.4 1 0 0 1.5 1 0 1 1.575 1 1 0 1.8 1 1 1 1.875 continuous conduction and oscillator synchronization the SC198 is designed to operate in a continuous conduction mode, where it maintains a xed frequency. when the sync pin is tied high, the part runs under control of the internal oscillator in pwm mode. the part can be synchronized to an external clock by connecting a clock signal to the sync pin. the part synchronizes to the rising edge of the clock. power-save mode operation the SC198 has a power-save mode (psave) which may be selected by tying the sync pin to gnd. selecting psave mode enables automatic activation of psave mode at light loads, thus maximizing ef ciency across the full load range. the SC198 will automatically detect the load current at which it should enter psave mode. the SC198 is optimized to track maximum ef ciency with respect to v in .
applications information (cont.) 8 ? 2006 semtech corp. www.semtech.com SC198 power management v out upper threshold limit psave mode at light load pwm mode at medium/ high load psave exit threshold burst off higher load applied 0 a inductor current time lower threshold limit psave operation in psave mode, v out regulation is controlled by bursts in switching. while the output voltage is between the low and high voltage thresholds, switching is stopped to reduce loss in the regulator due to switching. when the voltage drops to the lower threshold, the switch bursts at a xed on time until the upper threshold is met. at this point the output voltage is allowed to ramp down to the lower threshold again without switching to conserve power. in the psave mode, less switching is used. less switching results in less power loss which can be seen in the difference of ef ciency between pwm mode and psave mode at light loads. the psave switching burst frequency is controlled such that the inductor current ripple during the burst is similar to that in pwm mode. the minimum switching frequency during this period is limited to 650khz. the SC198 automatically detects when to exit psave mode. the device sets a maximum peak current in psave mode, and then detects when v out falls due to the load increasing above the level that the peak current will support. for the SC198 to exit psave mode, the load must be increased, which causes v out to decrease until the psave exit threshold is reached. psave levels are set high to minimize the undershoot when the SC198 exits psave. protection features the SC198 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 SC198 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 frequen- cy foldback mode, that causes the switching frequency to divide by a factor determined by the output voltage. this prevents the inductor current from ?staircasing?. over-voltage protection over-voltage protection is provided on the SC198. hysteresis is provided to prevent toggling in and out of operation. soft-start the soft-start mode operates by limiting the current through the inductor and controlling the switching frequency. the current limit is increased over several milliseconds the in discrete steps. this has the desired effect of limiting in- rush current from the input supply. the soft-start mode is cancelled once the output reaches regulation. soft-start is only re-enabled by power cycling, toggling enable, uvlo event, or shutdown.
applications information (cont.) 9 ? 2006 semtech corp. www.semtech.com SC198 power management inductor selection the SC198 was designed for optimum performance when using 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 in- put voltage, output voltage, and inductor ripple current. the inductor should also have a low dcr to minimize the conduction losses and maximize ef ciency. the minimum 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 con- siderations such as ef ciency, emi, size and cost. table b lists some manufactuers of practical inductor options. capacitor selection input capacitor the source input current to a buck converter is non-on- tinuous. to prevent large input voltage ripple a low esr ceramic capacitor is required. a minimum value of 4.7 f should be used for suf cient input voltage ltering and a 22 f mlcc may be used for optimum input voltage lter- ing. output capacitor a 4.7 f ceramic capacitor is the minimum recommended for the output lter capacitor. a capacitor value of at least 10 f is recommended if the part will be used in power- save mode. output voltage ripple is dominated by the l- ter capacitance esr as shown in the following equation: v out(p-p) = i l 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 unsuit- able for this application. table c lists some manufactur- ers of recommended capacitor options.
applications information (cont.) 10 ? 2006 semtech corp. www.semtech.com SC198 power management table b ? recommended inductors manufacturer part number value h dcr rated current a tolerance % dimensions (lwh) mm coilcraft lpo6610-472ml (1) 4.7 0.20 1.1 20 6.60 5.50 1.10 1812ps-472klb 4.7 0.11 2.10 20 5.87 4.89 3.81 tdk vlcf4018t- 4r7n1r0-2 4.7 0.101 1.07 30 4.3 4.0 1.8 bi technologies hm66304r7 4.7 0.072 1.32 20 4.7 4.7 3.0 table c ? recommended capacitors manufacturer part number value f rated voltage vdc type % case size murata grm 21br60j226me39l 22 6.3 x5r 0805 grm188r60j106mke19 10 6.3 x5r 0603 grm188r60g106me47 4.7 6.3 x5r 0603 tdk c2012x5r0j106k 10 6.3 x5r 0603 note: (1) this inductor was used while obtaining data for the typical characteristics section.
applications information (cont.) gnd vin lxa lxb gnd SC198 cina cinb vouta voutb cinr note: control pin routings are not shown. pcb layout considerations poor layout can degrade the performance of the dc-dc converter and can be a contributory factor in emi problems, ground bounce, thermal issues, and resistive voltage losses. poor regulation and instability can result. the following design rules are recommended: place the inductor and lter capacitors as close to the device as possible and use short wide traces between the power components. route the output voltage feedback path away from inductor and lx node to minimize noise and magnetic interference. use a ground plane to further reduce noise interference on sensitive circuit nodes. 1. 2. 3. 11 ? 2006 semtech corp. www.semtech.com SC198 power management
typical characteristics 12 ? 2006 semtech corp. www.semtech.com SC198 power management 0 10 20 30 40 50 60 70 80 90 100 0.001 0.01 0.1 1 load (a) efficiency (%) v out = 1v pwm v out = 1.8v pwm v out = 1v psave v out = 1.8v psave ena=enb=vin 0 10 20 30 40 50 60 70 80 90 100 0.001 0.01 0.1 1 load (a) efficiency (%) v out = 1v psave v out = 1.8v pwm v out = 1v pwm v out = 1.8v psave ena=enb=vin -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 2.73.13.53.94.34.75.15.5 input (v) output (%) v out = 1v v out = 1.8v -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 0.001 0.01 0.1 1 load (a) output (%) v out = 1.8v v out = 1v ef ciency vs. load @ 2.7v in ef ciency vs. load @ 3.6v in ef ciency vs. load @ 5.5v in line regulation at 300ma out load regulation at 3.6v in (pwm) 0 10 20 30 40 50 60 70 80 90 100 0.001 0.01 0.1 1 load (a) efficiency (%) v out = 1v psave v out = 1v pwm v out = 1.8v pwm v out = 1.8v psave ena=enb=vin -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 input (v) normalized frequency (khz) -40c 85c 25c oscillator frequency vs. input voltage
typical characteristics (cont.) ef ciency vs. line @ v out = 1.8v ef ciency vs. line @ v out = 1v 50 60 70 80 90 100 2.7 3.7 4.7 input (v) efficiency (%) 300ma load 30ma pwm 30ma psave output ripple for v in = 3.6v and v out = 1.8v @ i out = 10ma output ripple for v in = 3.6v and v out = 1.8v @ i out = 50ma 20mv/div 2.0v/div 20mv/div 2.0v/div 400ns/div 400ns/div 10mv/div 10mv/div vin vout lx vin vout lx psave @ 50ma load psave @ 30ma load 2ms/div 2ms/div 50mv/div 50mv/div 2v/div 50mv/div 2v/div 50mv/div vin lx vout vout vin lx 13 ? 2006 semtech corp. www.semtech.com SC198 power management 50 60 70 80 90 100 2.7 3.7 4.7 input (v) efficiency (%) 300ma load 30ma pwm 30ma psave
psave @ 50ma load with c out = 22 f transient step in psave 50mv/div 2.0v/div 200mv/div 200ma/div 400 s/div 200mv/div 50mv/div 4.0 s/div iout lx vin vout 5.0v/div input transient step from 3.1v to 3.6v input transient step from 3.6v to 3.1v 1ms/div 1ms/div 500mv/div 20mv/div 500mv/div 20mv/div vin vout vin vout typical characteristics (cont.) output transient @ pwm output transient in psave 2ms/div 2ms/div 50mv/div 50mv/div 2v/div 2v/div vin vout lx c vouta ctl0 1 and 2 vouta ctl0 1 and 2 14 ? 2006 semtech corp. www.semtech.com SC198 power management
outline drawing - mlpq-20 4 x 4 .001 max .002 - .040 nom 0.80 0.02 (0.20) 0.90 controlling dimensions are in millimeters (angles in degrees). coplanarity applies to the exposed pad as well as the terminals. notes: 2. 1. 1 2 n e1 .100 .106 .110 2.55 2.70 2.80 pin 1 indicator 4.10 3.90 4.00 4.10 3.90 .157 .153 .161 .153 .161 aaa c a c (laser mark) d e b a1 a a2 seating plane lxn e/2 bxn bbb c a b e d/2 d1 e1 inches .020 bsc b .007 bbb aaa n d1 e l e d .011 .100 dim a1 a2 a min .000 - .031 0.30 0.18 .012 0.25 .010 0.50 2.80 0.30 2.55 .004 .004 20 .016 .157 .106 .020 .110 0.10 0.10 20 0.40 4.00 2.70 0.50 bsc millimeters max 0.05 - 1.00 dimensions min 0.00 - nom (.008) .035 15 ? 2006 semtech corp. www.semtech.com SC198 power management
land pattern - mlpq-20 4 x 4 dimensions k h g z x p (c) company's manufacturing guidelines are met. 4.80 .189 z y this land pattern is for reference purposes only. consult your manufacturing group to ensure your notes: 1. dim x y h k p c g millimeters inches (3.95) .010 .033 .122 .021 .106 .106 (.155) 0.25 0.85 2.70 0.50 2.70 3.10 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 16 ? 2006 semtech corp. www.semtech.com SC198 power management

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