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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 5 287 (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 9 287 287 ? ? ? ? = ? (2) the percentage error of a v out = 5v converter with r 1 = 100k ? and r 2 = 301k ? is ( ) 9 n n q$ 9 9 287 287 ? = ? ? ? ? = ? 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: ' 287 &(6$7 ' 287 ,1 9 9 9 9 9 9 ' + ? + ? = (3) where v cesat is the switch saturation voltage and v d is volt- age drop across the rectifying diode. maximum output current in a boost switching regulator the inductor is connected to the input. the inductor dc current is the input current. when the power switch is turned on, the inductor current ows into the switch. when the power switch is off, the inductor current ows through the rectifying diode to the output. the output current is the average diode current. the diode current waveform is trapezoidal with pulse width (1 ? d)t (see figure 4). the output current available from a boost converter therefore depends on the converter oper- ating duty cycle. the power switch current in the sc4503 is internally limited to at least 1.4a. this is also the maximum peak inductor or the peak input current. by estimating the conduction losses in both the switch and the diode, an expression of the maximum available output current of a boost converter can be derived: () ? ? o ? ? a ? ? ? ? = ,1 &(6$7 ' ' 287 ,1 /,0 2870$; 9 9 9 ' 9 ' 9 9 , , (4) switch current diode current on on off on on off on off (1-d)t dt inductor current 0 0 in i out i switch current diode current on on off on on off on off (1-d)t dt inductor current 0 0 in i out i figure 4. current waveforms in a boost converter figure 4. current waveforms in a boost converter switch current diode current on on off on on off on off (1-d)t dt inductor current 0 0 in i out i switch current diode current on on off on on off on off (1-d)t dt inductor current 0 0 in i out i figure 4. current waveforms in a boost converter figure 4. current waveforms in a boost converter where i lim is the switch current limit. it is worth noting that i outmax is directly proportional to the ratio 287 ,1 9 9 and that switching losses are neglected in its derivation. equation (4) therefore over-estimates the maximum output current, however it is a useful rst-order approximation. using v cesat = 0.3v, v d = 0.5v and i lim =1.4a in (3) and (4), the maximum output current for three v in and v out combi- nations are tabulated (table 1). maximum duty-cycle limitation the power transistor in the sc4503 is turned off every switching period for 80ns. this minimum off time limits the maximum duty cycle of the regulator. a boost converter with high ,1 287 9 9 ratio requires long switch on time and high duty cycle. if the required duty cycle is higher than the attain- able maximum, then the converter will operate in dropout. (dropout is a condition in which the regulator cannot attain its set output voltage below current limit.) note: dropout can occur when operating at low input volt- ages (<3v) and with off times approaching 100ns. shorten the pcb trace between the power source and the device input pin, as line drop may be a signi cant percentage of the input voltage. a regulator in dropout may appear as if it is in current limit. the cycle-by-cycle current limit of the sc4503 is duty-cycle and input voltage invariant and should be at least 1.4a. if the converter output is below its set value and switch current limit is not reached (1.4a), then the converter is likely in dropout. example : determine the highest attainable output voltage when boosting from a single li-ion cell. equation (3) can be re-arranged as: table 1. calculated maximum output currents v in (v) v out (v) d i out (a) 3.3 12 0.754 0.34 3.3 5 0.423 0.80 5 12 0.615 0.53 v in (v) v out (v) d i out (a) 3.3 12 0.754 0.34 3.3 5 0.423 0.80 5 12 0.615 0.53 table 1. calculated maximum output currents v in (v) v out (v) d i out (a) 3.3 12 0.754 0.34 3.3 5 0.423 0.80 5 12 0.615 0.53 v in (v) v out (v) d i out (a) 3.3 12 0.754 0.34 3.3 5 0.423 0.80 5 12 0.615 0.53
10 ? 2007 semtech corp. www.semtech.com power management sc4503 ' &(6$7 ,1 287 9 ' ' 9 9 9 ? ? ? = (5) assuming that the voltage of a nearly discharged li-ion cell is 2.6v. using v d =0.5v, v cesat =0.3v and d=0.86 in (5), 9 9 287 = ? ? ? ? < transient headroom requirement further reduces the maxi- mum achievable output voltage to below 16v. minimum controllable on-time the operating duty cycle of a boost converter decreases as v in approaches v out . sensed switch current ramp modulates the pulse width in a current-mode switching regulator. this current ramp is absent unless the switch is turned on. the intersection of this ramp with the error ampli er output determines the switch on-time. the propagation delay time required to immediately turn off the switch after it is turned on is the minimum controllable on time. measured minimum on time of the sc4503 is load-dependent and ranges from 180ns to 220ns at room temperature. the switch in the sc4503 is either not turned on, or, for at least this minimum. if the regulator requires a switch on-time less than this controllable minimum, then it will either skip cycles or start to jitter. inductor selection the inductor ripple current i l of a boost converter in con- tinuous-conduction mode is ( ) i/ 9 9 ' , &(6$7 ,1 / ? = ? (6) where f is the switching frequency and l is the induc- tance. substituting (3) into (6) and neglecting v cesat , ? ? 1 ? + ? = ? ' 287 ,1 ,1 / 9 9 9 i/ 9 , (7) in current-mode control, the slope of the modulating (sensed switch current) ramp should be steep enough to applications information (cont.) lessen jittery tendency but not so steep that large ux swing decreases ef ciency. for continuous-conduction mode operation, inductor ripple current i l between 0.35a and 0.6a is a good compromise. setting i l = 0.43a, v d = 0.5v and f = 1.3mhz in (7), ? ? 1 ? + ? = ? ? 1 ? + ? ? = 9 9 9 9 9 9 , i 9 / 287 ,1 ,1 ' 287 ,1 / ,1 (8) where l is in h. equation (7) shows that for a given v out , i l is the highest when ( ) 9 9 9 ' 287 ,1 + = . if v in varies over a wide range, then choose l based on the nominal input voltage. the saturation current of the inductor should be 20-30% higher than the peak current limit (1.9 a). low-cost powder iron cores are not suitable for high-frequency switching power supplies due to their high core losses. inductors with ferrite cores should be used. discontinuous-conduction mode the output-to-input voltage conversion ratio ,1 287 9 9 0 = in continuous-conduction mode is limited by the maximum duty cycle d max : ' 0 0$; = ? = ? < ' 0 0$; = ? = ? < higher voltage conversion ratios can be achieved by oper- ating the boost converter in full-time discontinuous-con- duction mode (dcm). de ne out out i v r = as the equivalent output load resistance. the following inequalities must be satis ed for dcm operation: 0 0 5 /i ? < (9) and, 0 $ 5 9 , 287 287 < = (10)
11 ? 2007 semtech corp. www.semtech.com sc4503 power management switch on duty ratio in dcm is given by, 0 0 5 /i ' ? = (11) higher input current ripples and lower output current are the drawbacks of dcm operation. input capacitor the input current in a boost converter is the inductor cur- rent, which is continuous with low rms current ripples. a 2.2-4.7 f ceramic input capacitor is adequate for most applications. output capacitor both ceramic and low esr tantalum capacitors can be used as output ltering capacitors. multi-layer ceramic capacitors, due to their extremely low esr (<5m ), are the best choice. use ceramic capacitors with stable temperature and voltage characteristics. one may be tempted to use z5u and y5v ceramic capacitors for output ltering because of their high capacitance density and small sizes. however these types of capacitors have high temperature and high voltage coef cients. for example, the capacitance of a z5u capacitor can drop below 60% of its room temperature value at ?25c and 90c. x5r ceramic capacitors, which have stable temperature and voltage coef cients, are the preferred type. the diode current waveform in figure 4 is discontinuous with high ripple-content. unlike a buck converter in which the inductor ripple current ? i l determines the output ripple voltage. the output ripple voltage of a boost regulator is much higher and is determined by the absolute inductor current. decreasing the inductor ripple current does not reduce the output ripple voltage appreciably. the current flowing in the output filter capacitor is the difference between the diode current and the output current. this capacitor current has a rms value of: 9 9 , ,1 287 287 ? (12) if a tantalum capacitor is used, then its ripple current rating in addition to its esr will need to be considered. applications information (cont.) when the switch is turned on, the output capacitor supplies the load current i out (figure 4). the output ripple voltage due to charging and discharging of the output capacitor is therefore: 287 287 287 & '7 , 9 = ? (13) for most applications, a 10-22 f ceramic capacitor is suf- cient for output ltering. it is worth noting that the output ripple voltage due to discharging of a 10 f ceramic capaci- tor (13) is higher than that due to its esr. rectifying diode for high ef ciency, schottky barrier diodes should be used as rectifying diodes for the sc4503. these diodes should have an average forward current rating at least equal to the output current and a reverse blocking voltage of at least a few volts higher than the output voltage. for switching regulators operating at low duty cycles (i.e. low output voltage to input voltage conversion ratios), it is bene cial to use rectifying diodes with somewhat higher average cur- rent ratings (thus lower forward voltages). this is because the diode conduction interval is much longer than that of the transistor. converter ef ciency will be improved if the voltage drop across the diode is lower. the rectifying diodes should be placed close to the sw pin of the sc4503 to minimize ringing due to trace induc- tance. surface-mount equivalents of 1n5817 and 1n5818, mbrm120, mbr0520l, zhcs400, 10bq015 and equiva- lent are suitable. shutdown and soft-start the shutdown ( ss shdn ss shdn ) pin is a dual function pin. when driven from a logic gate with v oh >2v, the ss shdn ss shdn pin functions as an on/off input to the sc4503. when the shutdown pin is below 2v, it clamps the error ampli er output to 66 6+'1 9 66 6+'1 9 and reduces the switch current limit. connecting r ss and c ss to the ss shdn ss shdn pin (figure 5) slows the voltage rise at the pin during start-up. this forces the peak inductor current (hence the input current) to follow a slow ramp, thus achieving soft-start.
12 ? 2007 semtech corp. www.semtech.com power management sc4503 methods of driving the shutdown pin and soft-starting the sc4503 (a) directly driven from a logic gate. r lim limits the gate output current during fault, (b) soft-start only, (c) driven from a logic gate with soft-start, (d) driven from a logic gate with soft-start (1.7v < v oh < 2v), (e) driven from an open-collector npn transistor with soft-start and (f) driven from a logic gate (whose v oh > v in ) with soft-start. figure 5. applications information (cont.) the minimum ss shdn ss shdn voltage for switching is 1.4v. the graph ?switch current limit vs. shutdown pin voltage? in the ?typical characteristics? shows that the ss shdn ss shdn pin voltage needs to be at least 2v for the sc4503 to deliver its rated power. the effect of the ss shdn ss shdn voltage on the sc4503 is analog between 1.4v and 2v. within this range the switch current limit is determined not by ilim but in- stead by the pwm signal path (see figure 2). moreover it varies with duty cycle and the shutdown pin voltage. pulling the ss shdn ss shdn pin below 0.4v shuts down the sc4503, drawing less than 1a from the input power supply. for voltages above 2v and below 0.4v, the ss shdn ss shdn pin can be regarded as a digital on/off input. figure 5 shows several ways of interfacing the control logic to the shutdown pin. in figure 5(a) soft-start is not used and the logic gate drives the shutdown pin through a small ( 1k ? ) optional resistor r ss . r ss limits the current drawn by the sc4503 internal (a) sc4503 shdn/ss in v oh > 2v v ol < 0.4v r lim sc4503 shdn/ss in v ol < 0.4v r ss c ss i shdn/ss end of soft-start v shdn/ss > 2v (c) (b) sc4503 in shdn/ss c ss r ss end of soft-start v shdn/ss > 2v v in sc4503 in shdn/ss c ss r ss end of soft-start v shdn/ss > 2v v in (e) (d) sc4503 shdn/ss in v ol 0 c ss i shdn/ss r ss cmdsh-3 d ss 1.7v < v oh < 2v v in (f) 1n4148 sc4502 in v in r ss c ss v oh > v in shdn/ss
13 ? 2007 semtech corp. www.semtech.com sc4503 power management applications information (cont.) circuit from the driving logic gate during fault condition. in figure 5(f) the shutdown pin is driven from a logic gate whose v oh is higher than the supply voltage to the sc4503. the diode clamps the maximum shutdown pin voltage to one diode voltage above the input power supply. during soft-start, c ss is charged by the difference between the r ss current and the shutdown pin current, 66 6+'1 , 66 6+'1 , . in steady state, the voltage drop across r ss reduces the shut- down pin voltage according to the following equation: 66 6+'1 66 (1 66 6+'1 , 5 9 9 ? = 66 6+'1 66 (1 66 6+'1 , 5 9 9 ? = (14) in order for the sc4503 to achieve its rated switch current, 66 6+'1 9 66 6+'1 9 must be greater than 2v in steady state. this puts an upper limit on r ss for a given enable voltage v en (= voltage applied to r ss ). the maximum speci ed 66 6+'1 , 66 6+'1 , is 50 a with 9 9 66 6+'1 = 9 9 66 6+'1 = (see ?electrical characteristics?). the largest r ss can be found using (14): $ 9 5 0,1 (1 66 ? < $ 9 5 0,1 (1 66 ? < if the enable signal is less than 2v, then the interfacing options shown in figures 5(d) and 5(e) will be preferred. the methods shown in figures 5(a) and 5(c) can still be used however the switch current limit will be reduced. variations of 66 6+'1 , 66 6+'1 , and switch current limit with ss shdn ss shdn pin voltage and temperature are shown in the ?typical characteristics?. shutdown pin current decreases as temperature increases. switch current limit at a given 66 6+'1 9 66 6+'1 9 also decreases as temperature rises. lower shutdown pin current owing through r ss at high temperature results in higher shutdown pin voltage. however reduction in switch current limit (at a given 66 6+'1 9 66 6+'1 9 ) at high temperature is the dominant effect. feed-forward compensation figure 6 shows the equivalent circuit of a boost converter. important poles and zeros of the overall loop response are: low frequency integrator pole, & 2 s & 5 ? = , output lter pole, 287 287 s 5& & 9 , ? = ? = 287 287 s 5& & 9 , ? = ? = , compensating zero, & & = & 5 ? = & & = & 5 ? = and right half plane (rhp) zero, () / ' 5 = ? = () / ' 5 = ? = . the poles p 1 , p 2 and the rhp zero z 2 all increase phase shift in the loop response. for stable operation, the over- all loop gain should cross 0db with -20db/decade slope. due to the presence of the rhp zero, the 0db crossover frequency should not be more than ] . the internal compensating zero z 1 provides phase boost beyond p 2 . in general the converter is more stable with widely spaced lter pole p 2 and the rhp zero z 2 . the rhp zero moves to low frequency when either the duty-cycle d or the output current i out increases. it is bene cial to use small inductors and larger output capacitors especially when operating at high ,1 287 9 9 ,1 287 9 9 ratios. a feed-forward capacitor c 4 is needed for stability. the value of c 4 can be determined empirically by observing the induc- tor current and the output voltage during load transient. starting with a value between 5 v 5 v and 5 v 5 v , c 4 is adjusted until there is no excessive ringing or overshoot in inductor current and output voltage during load transient. sizing the inductor such that its ripple current is about 0.5a also improves phase margin and transient response. power stage reference voltage 1.252v gm - + r c c c r o r2 comp r1 fb c4 esr c2 r v out v in i out r o is the equivalent output resistance of the error amplifier power stage reference voltage 1.252v gm - + r c c c r o r2 comp r1 fb c4 esr c2 r v out v in i out r o is the equivalent output resistance of the error amplifier simpli ed equivalent model of a boost converter figure 6. simpli ed equivalent model of a boost converter figure 6. power stage reference voltage 1.252v gm - + r c c c r o r2 comp r1 fb c4 esr c2 r v out v in i out r o is the equivalent output resistance of the error amplifier power stage reference voltage 1.252v gm - + r c c c r o r2 comp r1 fb c4 esr c2 r v out v in i out r o is the equivalent output resistance of the error amplifier simpli ed equivalent model of a boost converter figure 6. simpli ed equivalent model of a boost converter figure 6.
14 ? 2007 semtech corp. www.semtech.com power management sc4503 applications information (cont.) figures 7(a)-7(c) show the effects of different values of inductance and feed-forward capacitance on transient re- sponses. in a battery-operated system if c 4 is optimized for the minimum v in and the maximum load step, the converter will be stable over the entire input voltage range. different inductances and feed-forward capaci- tances affect the load transient responses of the 3.3v to 12v step-up converter in figure 10(a). i out is switched between 90ma and 280ma. figure 7. i l1 0.5a/div v out 0.5v/div 40 s/div (a) l 1 = 5.6 h and c 4 = 2.2pf 40 s/div i l1 0.5a/div v out 0.5v/div (b) l 1 = 5.6 h and c 4 = 3.3pf 40 s/div i l1 0.5a/div v out 0.5v/div (c) l 1 = 3.3 h and c 4 = 2.7pf board layout considerations in a step-up switching regulator, the output lter capacitor, the main power switch and the rectifying diode carry pulse currents with high di/dt. for jitter-free operation, the size of the loop formed by these components should be minimized. since the power switch is integrated inside the sc4503, grounding the output lter capacitor next to the sc4503 ground pin minimizes size of the high di/dt current loop. the input bypass capacitors should also be placed close to the input pins. shortening the trace at the sw node reduces the parasitic trace inductance. this not only reduces emi but also decreases switching voltage spikes. figure 8 shows how various external components are placed around the sc4503. the large surrounding ground plane acts as a heat sink for the device. shdn/ss l1 d1 r3 c3 u1 gnd r2 vin vout jp c1 r1 c4 c2 sw fb figure 8. suggested pcb layout for the sc4503.
15 ? 2007 semtech corp. www.semtech.com sc4503 power management l1: murata lqh32c c1: murata grm219r60j475k 5v c1 4.7 f zhcs400 d1 0.22 f c2 c5 22nf l1 c3 56nf 10 h sc4503 3 1 5 2 gnd shdn/ss in sw fb 4 c4 220pf r1 63.4 301k r4 r2 63.4 d2 24v _ + mm5z24vt1 r3 54.9k driving two 6 white led strings from 5v. zener diode d 2 protects the converter from over-voltage damage when both led strings become open. figure 9. typical application circuits
16 ? 2007 semtech corp. www.semtech.com power management sc4503 typical application circuits 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 figure 10(b). ef ciency vs load current upper trace : output voltage, ac coupled, 0.5v/div lower trace : input inductor current, 0.5a/div load transient response of the circuit in figure 10(a). i out is switched between 90ma and 280ma figure 10(c). 40 s/div 2.2 f c1 3.3v vin vout sc4503 3 1 5 2 gnd shdn/ss in sw fb 4 10bq015 d1 l1 c2 4.7 f r2 100k r1 866k 12v 2.7 h r3 15k c3 56nf c4 2.2pf figure 10(a) . 3.3v to 12v boost converter with soft-start l1: coiltronics ld1 c1: murata grm188r61a225k c2: murata grm21br61c475k
17 ? 2007 semtech corp. www.semtech.com sc4503 power management typical application circuits vout c1 4.7 f sc4503 3 1 5 2 gnd shdn/ss in sw fb 4 10bq015 d1 l1 c2 10 f r2 60.4k r1 187k 5v 1.5 h r3 15k c3 56nf 2.6 - 4.2v 1-cell li-ion on off 3.3v < 0.4v c4 10pf 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 = 5v 1.3mhz v in = 3.6v v in = 2.6v v in = 4.2v upper trace : output voltage, ac coupled, 0.2v/div lower trace : inductor current, 0.5a/div upper trace : output voltage, ac coupled, 0.2v/div lower trace : inductor current, 0.5a/div load transient response. i out is switched between 0.15a and 0.9a figure 11(d). load transient response. i out is switched between 0.1a and 0.5a figure 11(c). v in = 2.6v v in = 4.2v 40 s/div 40 s/div ef ciency of the li-ion cell to 5v boost converter figure 11(b). figure 11(a). single li-ion cell to 5v boost converter l1: tdk vlf4012at c1: murata grm188r60j475k c2: murata grm21br60j106k
18 ? 2007 semtech corp. www.semtech.com power management sc4503 typical application circuits 2.6 - 4.2v vout c1 1 f 10bq015 d1 c2 10 f r2 249k r1 412k 3.3v, 0.45a l1 3.3 h c5 2.2 f l2 3.3 h sc4503 3 1 5 2 gnd shdn/ss in sw fb 4 r3 8.06k c3 c4 15pf 1-cell li-ion 0.22 f efficiency vs load current 30 35 40 45 50 55 60 65 70 75 80 85 0.001 0.010 0.100 1.000 load current (a) efficiency (%) v out = 3.3v v in = 3.6v v in = 2.6v v in = 4.2v v in = 3.6v l1 and l2: coiltronics drq73-3r3 c1: murata grm188r61a105k c2: murata grm21br60j106k c5: murata grm188r61a225k figure 12(b). ef ciency vs load current upper trace : output voltage, ac coupled, 0.2v/div lower trace : input inductor current, 0.2a/div load transient response of the circuit in figure 12(a). i out is switched between 100ma and 500ma figure 12(c). 40 s/div figure 12(a). single li-ion cell to 3.3v sepic converter.
19 ? 2007 semtech corp. www.semtech.com sc4503 power management typical application circuits 3.3v 26v (10ma) c1 4.7 f out1 10bq015 d1 4.7 f x 2 r1 c2 r2 49.9k 309k 9v (0.3a) c9 0.1 f d6 d7 c10 1 f d2 0.1 f c5 d3 0.1 f c6 d4 0.1 f c7 d5 1 f c8 out2 out3 -8.5v (10ma) l1 c3 56nf 4.7 h 17.8k r3 sc4503 3 1 5 2 gnd shdn/ss in sw fb 4 3.3v < 0.4v on off c4 12pf run d2 - d7 : bat54s l1 : sumida cdc5d23b-4r7m c2: murata grm21br61c475k c1: murata grm188r61a105k figure 13(a). triple-output tft power supply with soft-start ch3 ch2 ch1 ch4 ch1 : out1 voltage, 5v/div ch2 : out2 voltage, 20v/div ch3 : out3 voltage, 5v/div ch4 : run voltage, 5v/div 400 s/div upper trace : output voltage, ac coupled, 0.5v/div lower trace : inductor current, 0.5a/div 40 s/div tft power supply start-up transient as the run voltage is stepped from 0 to 3.3v figure 13(b). load transient response. i out1 is switched between 50ma and 350ma figure 13(c).
20 ? 2007 semtech corp. www.semtech.com power management sc4503 evb schematic r1 0r c2 n.p. r4 0r off/on r3 47k 5vin 12vout l1 4.7uh c4 15pf c3 10uf d1 ss13 u1 sc4503 1 2 34 5 sw gnd fb shdn vin c1 10uf r5 49.9k r2 432k c5 100n jp1 c1 10uf l1 4.7uh jp1 r5 49.9k 12vout off/on r3 47k d1 ss13 c4 15pf c3 10uf 5vin r4 0r c2 n.p. u1 sc4503_mlpd 1 2 3 4 5 6 7 8 sw sw vin shdn/ss fb gnd gnd n.c. c5 100nf r2 432k r1 0r
21 ? 2007 semtech corp. www.semtech.com sc4503 power management .110 bsc .037 bsc detail ccc c 2x n/2 tips 2x e/2 5 see detail a .008 12 n e .060 .114 .063 .118 .012 - 5 a 0.20 1.60 3.00 2.80 bsc 0.95 bsc .067 1.50 2.90 .020 0.30 1.70 0.50 - l (l1) c 01 0.25 plane gage 2.80 .110 0 .010 - .004 .012 .003 (.024) .018 - .028 .000 - - - - 0.10 0.25 8 0 - 8 - (0.60) 0.45 .024 .008 0.30 0.08 .039 .035 .004 0.00 0.70 - 0.20 0.60 - 0.10 1.00 0.90 - - 1.90 bsc .075 bsc seating aaa c bbb c a-b d a bxn a2 a1 d dimensions "e1" and "d" do not include mold flash, protrusions 3. or gate burrs. datums and to be determined at datum plane controlling dimensions are in millimeters (angles in degrees). -b- notes: 1. 2. -a- -h- side view a b d e1 e c h plane e1 reference jedec std mo-193, variation ab. 4. nom inches dimensions l1 ccc aaa bbb 01 n dim c e e1 l e1 e d a1 a2 b a min millimeters max min nom max outline drawing - tsot-23 land pattern - tsot-23 dimensions inches y z dim g p x c millimeters p (c) z y g .055 .141 .031 (.087) .037 .024 0.80 (2.20) 0.95 0.60 1.40 3.60 x this land pattern is for reference purposes only. consult your manufacturing group to ensure your company's manufacturing guidelines are met. notes: 1. dimensions inches y z dim g p x c millimeters
22 ? 2007 semtech corp. www.semtech.com power management sc4503 outline drawing - 8 lead 2x2mm mlpd-w land pattern - 8 lead 2x2mm mlpd-w 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 2.00 .079 pin 1 indicator (laser mark) a1 seating plane c b a aaa c 1 n e 2.10 2.10 1.90 1.90 .083 .083 .075 .075 a 2 inches .020 bsc b .007 bbb aaa n l e d .008 dim a1 a2 min .000 .028 0.30 0.18 .012 0.25 .010 0.40 0.20 .003 .003 8 .012 .079 .016 0.08 0.08 8 0.30 2.00 0.50 bsc millimeters max 0.05 0.80 dimensions min 0.00 nom (.008) .030 .001 max .002 .031 nom 0.70 0.02 (0.20) 0.75 controlling dimensions are in mi llimeters (angles in degrees). notes: 1. a2 d e/2 e bxn bbb c a b coplanarity applies to the exposed pad as well as the terminals. 2. d1 .059 .063 .067 1.50 1.60 1.70 e1 .031 .035 .039 0.80 0.90 1.00 d/2 e/2 e lxn e1 d1 a

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