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power management sc4503 1.3mhz step-up switching regulator with 1.4a switch the sc4503 is a 1.3mhz current-mode step-up switch- ing regulator with an integrated 1.4a power transistor. its high switching frequency allows the use of tiny sur- face-mount external passive components. the sc4503 features a combined shutdown and soft-start pin. the optional soft-start function eliminates high input current and output overshoot during start-up. the internal com- pensation network accommodates a wide range of volt- age conversion ratios. the internal switch is rated at 34v making the device suitable for high voltage applications such as boost and sepic. the sc4503 is available in low-pro le 5-lead tsot-23 and 8-lead 2x2mm mlpd-w packages. the sc4503?s low shutdown current (< 1 a), high frequency operation and small size make it suitable for portable applications. ? low saturation voltage switch: 260mv at 1.4a ? 1.3mhz constant switching frequency ? peak current-mode control ? internal compensation ? programmable soft-start ? input voltage range from 2.5v to 20v ? output voltage up to 27v ? uses small inductors and ceramic capacitors ? low shutdown current (< 1 a) ? low pro le 5-lead tsot-23 and 8-lead 2x2mm mlpd-w packages ? fully weee and rohs compliant ? local dc-dc converters ? tft bias supplies ? xdsl power supplies ? medical equipment ? digital cameras ? portable devices ? white led drivers 1 f c1 5v vin vout sc4503 3 1 5 2 gnd shdn/ss in sw fb 4 on off 10bq015 d1 l1 c2 4.7 f r2 49.9k r1 432k 12v, 0.5a 4.7 h c4 15pf efficiency vs load current 50 55 60 65 70 75 80 85 90 95 0.001 0.010 0.100 1.000 load current ( a ) efficiency (%) v out = 12v 1.3mhz www.semtech.com 1 may 4, 2007 description features typical application circuit features typical application circuit applications c1: murata grm188r61a105k c2: murata grm21br61c475k l1: sumida cdc5d23b-4r7 figure 1(a). 5v to 12v boost converter figure 1(b). ef ciency of the 5v to 12v boost converter
2 ? 2007 semtech corp. www.semtech.com power management sc4503 absolute maximum ratings 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. *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 jes d51 standards. electrical characteristics absolute maximum ratings unless speci ed: v in = v shdn/ss = 3v, -40c < t a = t j < 85c parameter symbol maximum units supply voltage v in -0.3 to 20 v sw voltage v sw -0.3 to 34 fb voltages v fb -0.3 to v in +0.3 shdn/ss voltage v shdn -0.3 to v in +1 thermal resistance junction to ambient (tsot - 23) ja 191* c/w thermal resistance junction to ambient (2x2 mm mlpd-w) ja 78* c/w maximum junction temperature t j 150 c storage temperature range t stg -65 to +150 lead temperature (soldering)10 sec (tsot - 23) t lead 260 peak ir re ow temperature (2x2mm mlpd-w) t ir 260 esd rating (human body model) esd 2000 v parameter conditions min typ max units under-voltage lockout threshold 2.2 2.5 v maximum operating voltage 20 feedback voltage 1.225 1.250 1.275 feedback line voltage regulation 2.5v < v in < 20v 0.02 %/v fb pin bias current -25 -50 na switching frequency 1.15 1.30 1.55 mhz minimum duty cycle 0 % maximum duty cycle 86 90 switch current limit 1.4 1.9 2.5 a switch saturation voltage i sw = 1.4a 260 430 mv switch leakage current v sw = 5v 0.01 1 a v in quiescent supply current v shdn/ss = 2v, v fb = 1.5v (not switching) 0.8 1.1 ma v in supply current in shutdown v shdn/ss = 0 0.01 1 a 3 ? 2007 semtech corp. www.semtech.com sc4503 power management parameter conditions min typ max units shdn/ss switching threshold v fb = 0v 1.4 v shutdown input high voltage 2 v shutdown input low voltage 0.4 shdn/ss pin bias current v shdn/ss = 2v 22 50 a v shdn/ss = 1.8v 20 45 v shdn/ss = 0v 0.1 thermal shutdown temperature 155 c thermal shutdown hysteresis 10 electrical characteristics (cont.) unless speci ed: v in = v shdn/ss = 3v, -40c < t a = t j < 85c pin con guration - tsot - 23 ordering information in fb gnd sw shdn/ss 5 4 1 2 3 top view device (1,2) top mark package sc4503tsktrt bh00 tsot-23 sc4503evb evaluation board 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. pin pin name pin functions 1sw collector of the internal power transistor. connect to the boost inductor and the freewheeling diode. the maximum switching voltage spike at this pin should be limited to 34v. 2 gnd ground. tie to ground plane. 3fb the inverting input of the error ampli er. tie to an external resistive divider to set the output volt- age. 4 shdn/ss shutdown and soft-start pin. pulling this pin below 0.4 shuts down the converter. applying more than 2v at this pin enables the sc4503. an external resistor and an external capacitor con- nected to this pin soft-start the switching regulator. the sc4503 will try to pull the shdn/ss pin below its 1.4v switching threshold regardless of the external circuit attached to the pin if vin is below the under-voltage lockout threshold. tie this pin through an optional resistor to in or to the output of a controlling logic gate if soft-start is not used. see applications information for more details. 5in power supply pin. bypassed with capacitor close to the pin. pin descriptions - tsot -23 5-lead tsot-23 4 ? 2007 semtech corp. www.semtech.com power management sc4503 8-lead 2x2mm mlpd-w device (1,2) top mark package SC4503WLTRT e00 2mmx2mm mlpd-w sc4503_mlpd evb evaluation board 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. ordering information pin descriptions - 2x2mm mlpd-w pin pin name pin functions 1,2 sw collector of the internal power transistor. connect to the boost inductor and the free- wheeling diode. the maximum switching voltage spike at this pin should be limited to 34v. 3 in power supply pin. bypassed with capacitor close to the pin. 4 shdn/ss shutdown and soft-start pin. pulling this pin below 0.4 shuts down the converter. apply- ing more than 2v at this pin enables the sc4503. an external resistor and an external capacitor connected to this pin soft-start the switching regulator. the sc4503 will try to pull the shdn/ss pin below its 1.4v switching threshold regardless of the external circuit attached to the pin if vin is below the under-voltage lockout threshold. tie this pin through an optional resistor to in or to the output of a controlling logic gate if soft-start is not used. see applications information for more details. 5fb the inverting input of the error ampli er. tie to an external resistive divider to set the output voltage. 6,7 gnd ground. tie to ground plane. 8 n.c. no connection. edp solder to the ground plane of the pcb. top view pin con guration - 2mm x 2mm mlpd 1 2 3 4 8 7 6 5 sw sw in shdn/ss nc gnd gnd fb 1 2 3 4 8 7 6 5 sw sw in shdn/ss nc gnd gnd fb 5 ? 2007 semtech corp. www.semtech.com sc4503 power management block diagram ref not ready ea - fb 2 reference voltage in 5 4 shdn/ss shutdown thermal 1.25v + + r q s pwm clk - + + + - isen ilim + - i - limit gnd 2 sw 1 oscillator slope comp r sense t > 155 c j 1v + - q1 d1 q2 z1 q3 figure 2. sc4503 block diagram 6 ? 2007 semtech corp. www.semtech.com power management sc4503 typical characteristics switching frequency vs temperature 1.0 1.1 1.2 1.3 1.4 1.5 -50-250 255075100125 temperature (c) frequency (mhz) fb voltage vs temperature 1.10 1.15 1.20 1.25 1.30 -50-25 0 255075100125 temperature (c) fb voltage (v) v in under-voltage lockout threshold vs temperature 1.6 1.8 2.0 2.2 2.4 2.6 -50-250 255075100125 temperature (c) uvlo threshold (v) switch current limit vs temperature 1.0 1.2 1.4 1.6 1.8 2.0 -50-25 0 255075100125 temperature (c) current limit (a) v shdn/ss = 3v switch saturation voltage vs switch current 0 100 200 300 400 0.0 0.5 1.0 1.5 2.0 switch current (a) v cesat (mv) 25c -40c 125c v in quiescent current vs temperature 0.60 0.65 0.70 0.75 0.80 -50-25 0 255075100125 temperature (c) v in current (ma) v fb = 1.5v 7 ? 2007 semtech corp. www.semtech.com sc4503 power management switch current limit vs shutdown pin voltage 0.0 0.5 1.0 1.5 2.0 2.5 1.2 1.4 1.6 1.8 2.0 shutdown pin voltage (v) current limit (a) 25c -40c 85c d = 50% switch current limit vs shutdown pin voltage 0.0 0.5 1.0 1.5 2.0 2.5 1.2 1.4 1.6 1.8 2.0 shutdown pin voltage (v) current limit (a) 25c -40c 85c d = 80% shutdown pin thresholds vs temperature 0.0 0.5 1.0 1.5 -50-250 255075100125 temperature (c) shdn thresholds (v) switching shutting down to i in < 1 a shutdown pin current vs shutdown pin voltage 0 10 20 30 40 50 0.0 0.5 1.0 1.5 2.0 2.5 3.0 shutdown pin voltage (v) shutdown pin current ( a) 25c -40c 85c shutdown pin current vs shutdown pin voltage 0 10 20 30 40 50 60 70 0 5 10 15 20 shutdown pin voltage (v) shutdown pin current ( a) 25c -40c 85c v in quiescent current vs shutdown pin voltage 0 200 400 600 800 1000 0.0 0.5 1.0 1.5 2.0 shutdown pin voltage (v) v in current ( a) 25c -40c 125c v in = 3v v fb = 1.5v typical characteristics (cont.) 8 ? 2007 semtech corp. www.semtech.com power management sc4503 applications information operation the sc4503 is a 1.3mhz peak current-mode step-up switching regulator with an integrated 1.4a (minimum) power transistor. referring to the block diagram, figure 2, the clock clk resets the latch and blanks the power transistor q 3 conduction. q 3 is switched on at the trailing edge of the clock. switch current is sensed with an integrated sense resistor. the sensed current is summed with the slope-compensat- ing ramp and fed into the modulating ramp input of the pwm comparator. the latch is set and q 3 conduction is terminated when the modulating ramp intersects the error ampli er (ea) output. if the switch current exceeds 1.9a (the typical current-limit), then the current-limit comparator ilim will set the latch and turn off q 3 . due to separate pulse- width modulating and current limiting paths, cycle-by-cycle current limiting is not affected by slope compensation. the current-mode switching regulator is a dual-loop feed- back control system. in the inner current loop the ea output controls the peak inductor current. in the outer loop, the error ampli er regulates the output voltage. the double reactive poles of the output lc lter are reduced to a single real pole by the inner current loop, allowing the internal loop compensation network to accommodate a wide range of input and output voltages. applying 0.9v at the ss shdn pin enables the voltage refer- ence. the signal ?ref not ready? does not go low until v in exceeds its under-voltage lockout threshold (typically 2.2v). assume that an external resistor is placed between the in and the ss shdn pins during startup. the voltage reference is enabled when the ss shdn voltage rises to 0.9v. before v in reaches 2.2v, ?ref not ready? is high. q 2 turns on and the zener diode z 1 loosely regulates the ss shdn voltage to 1v (above the reference enabling volt- age). the optional external resistor limits the current drawn during under-voltage lockout. when v in exceeds 2.2v, ?ref not ready? goes low. q 2 turns off, releasing ss shdn . if an external capacitor is connected from the ss shdn pin to the ground, the ss shdn voltage will ramp up slowly. the error ampli er output, which is clamped by d1 and q1, follows the voltage at the ss shdn pin. the input inductor current, which is in turn controlled by the error ampli er output, also ramps up gradually. soft-starting the sc4503 in this manner eliminates high input current and output overshoot. under fault condition (v in < 2.2v or over-temperature), the soft-start capacitor is discharged to 1v. when the fault condition disappears, the converter again undergoes soft-start. setting the output voltage an external resistive divider r 1 and r 2 with its center tap tied to the fb pin (figure 3) sets the output voltage. ? 1 ? ? = 9 9 5 5 2 8 7 (1) figure 3. r 1 - r 2 divider sets the output voltage the input bias current of the error ampli er will introduce an error of: ( ) 9 5 5 q $ 9 9 2 8 7 2 8 7 ? ? ? ? = ? (2) the percentage error of a v out = 5v converter with r 1 = 100k ? and r 2 = 301k ? is ( ) 9 n n q $ 9 9 2 8 7 2 8 7 ? = ? ? ? ? = ? this error is much less than the ratio tolerance resulting from the use of 1% resistors in the divider string. vout r2 r1 25na fb 3 sc4503 vout r2 r1 25na fb 3 sc4503 vout r2 r1 25na fb 3 sc4503 vout r2 r1 25na fb 3 sc4503 9 ? 2007 semtech corp. www.semtech.com sc4503 power management applications information (cont.) duty cycle the duty cycle d of a boost converter in continuous-conduc- tion mode (ccm) is: ' 2 8 7 & |