 |
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
| Datasheet File OCR Text: |
| 1.3MHz Step-Up Switching Regulator with 1.4A Switch POWER MANAGEMENT Description The SC4503 is a 1.3MHz current-mode step-up switching regulator with an integrated 1.4A power transistor. Its high switching frequency allows the use of tiny surface-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 compensation network accommodates a wide range of voltage 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-profile 5-lead TSOT-23 and 8-lead 2X2mm MLPD-W packages. The SC4503's low shutdown current (< 1A), high frequency operation and small size make it suitable for portable applications. SC4503 Features 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 (< 1A) Low Profile 5-Lead TSOT-23 and 8-Lead 2X2mm MLPD-W packages Fully WEEE and RohS compliant Applications Local DC-DC Converters TFT Bias Supplies XDSL Power Supplies Medical Equipment Digital Cameras Portable Devices White LED Drivers Typical Application Circuit Typical Application Circuit D1 10BQ015 1 SW SC4503 OFF ON 4 SHDN/SS GND 2 R2 49.9k FB 3 C4 15pF R1 432k C2 4.7F VIN 5V 5 IN C1 1F L1 4.7H VOUT 12V, 0.5A Efficiency vs Load Current 95 90 85 Efficiency (%) 1.3MHz 80 75 70 65 60 55 VOUT = 12V C1: Murata GRM188R61A105K C2: Murata GRM21BR61C475K L1: Sumida CDC5D23B-4R7 Figure 1(a). 5V to 12V Boost Converter May 4, 2007 1 50 0.001 0.010 0.100 1.000 Load Current (A) Figure 1(b). Efficiency of the 5V to 12V Boost Converter www.semtech.com SC4503 POWER MANAGEMENT Absolute Maximum Ratings Exceeding the specifications below may result in permanent damage to the device or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not recommended. Parameter Supply Voltage SW Voltage FB Voltages SHDN/SS Voltage Thermal Resistance Junction to Ambient (TSOT - 23) Thermal Resistance Junction to Ambient (2X2 mm MLPD-W) Maximum Junction Temperature Storage Temperature Range Lead Temperature (Soldering)10 sec (TSOT - 23) Peak IR Reflow Temperature (2X2mm MLPD-W) ESD Rating (Human Body Model) Symbol VIN VSW VFB VSHDN JA JA TJ TSTG TLEAD TIR ESD Maximum -0.3 to 20 -0.3 to 34 -0.3 to VIN +0.3 -0.3 to VIN +1 191* 78* 150 -65 to +150 Units V C/W C/W C 260 260 2000 V *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. Electrical Characteristics Unless specified: VIN = VSHDN/SS = 3V, -40C < TA = TJ < 85C Parameter Under-Voltage Lockout Threshold Maximum Operating Voltage Feedback Voltage Feedback Line Voltage Regulation FB Pin Bias Current Switching Frequency Minimum Duty Cycle Maximum Duty Cycle Switch Current Limit Switch Saturation Voltage Switch Leakage Current VIN Quiescent Supply Current VIN Supply Current in Shutdown 2007 Semtech Corp. Conditions Min Typ 2.2 Max 2.5 20 Units V 1.225 2.5V < VIN < 20V 1.250 0.02 -25 1.275 %/V -50 1.55 0 % nA MHz 1.15 1.30 86 1.4 ISW = 1.4A VSW = 5V VSHDN/SS = 2V, VFB = 1.5V (not switching) VSHDN/SS = 0 2 90 1.9 260 0.01 0.8 0.01 2.5 430 1 1.1 1 A mV A mA A www.semtech.com SC4503 POWER MANAGEMENT Electrical Characteristics (Cont.) Unless specified: VIN = VSHDN/SS = 3V, -40C < TA = TJ < 85C Parameter SHDN/SS Switching Threshold Shutdown Input High Voltage Shutdown Input Low Voltage Conditions VFB = 0V Min Typ 1.4 Max Units V V 2 0.4 VSHDN/SS = 2V 22 20 50 45 0.1 155 C 10 A SHDN/SS Pin Bias Current VSHDN/SS = 1.8V VSHDN/SS = 0V Thermal Shutdown Temperature Thermal Shutdown Hysteresis Pin Configuration - TSOT - 23 Top View SW GND FB 1 2 3 4 SHDN/SS 5 IN Ordering Information Device(1,2) SC4503TSKTRT SC4503EVB Top Mark BH00 Package TSOT-23 Evaluation Board 5-LEAD TSOT-23 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 Descriptions - TSOT -23 Pin 1 2 3 Pin Name SW GND FB Pin Functions 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. Ground. Tie to ground plane. The inverting input of the error amplifier. Tie to an external resistive divider to set the output voltage. 4 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 connected to this pin soft-start the switching regulator. The SC4503 will try to pull the SHDN/SS pin SHDN/SS 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. IN Power Supply Pin. Bypassed with capacitor close to the pin. 3 www.semtech.com 5 2007 Semtech Corp. SC4503 POWER MANAGEMENT Pin Configuration - 2mm X 2mm MLPD Top View Ordering Information Device(1,2) Top Mark E00 Package 2mmX2mm MLPD-W SW 1 8 NC SC4503WLTRT SC4503_MLPD EVB SW 2 7 GND Evaluation Board IN 3 6 GND SHDN/SS 4 5 FB 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. 8-LEAD 2X2mm MLPD-W Pin Descriptions - 2X2mm MLPD-W Pin 1,2 Pin Name SW Pin Functions 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. Power Supply Pin. Bypassed with capacitor close to the pin. 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 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. The inverting input of the error amplifier. Tie to an external resistive divider to set the output voltage. Ground. Tie to ground plane. No Connection. Solder to the ground plane of the PCB. 3 IN 4 SHDN/SS 5 6,7 8 EDP FB GND N.C. 2007 Semtech Corp. 4 www.semtech.com SC4503 POWER MANAGEMENT Block Diagram IN 5 SW 1 + Z1 REF NOT READY Q2 SHDN/SS 4 VOLTAGE REFERENCE THERMAL SHUTDOWN CLK T > 155C J 1V - 1.25V FB 2 + EA - - R S Q + PWM Q3 D1 Q1 ILIM + - I-LIMIT R SENSE + + ISEN + 2 GND OSCILLATOR SLOPE COMP Figure 2. SC4503 Block Diagram 2007 Semtech Corp. 5 www.semtech.com SC4503 POWER MANAGEMENT Typical Characteristics FB Voltage vs Temperature 1.30 1.5 1.4 Switching Frequency vs Temperature 1.25 Frequency (MHz) -50 -25 0 25 50 75 100 125 FB Voltage (V) 1.3 1.20 1.2 1.1 1.0 -50 -25 0 25 50 75 100 125 1.15 1.10 Temperature ( C) Temperature ( C) VIN Under-voltage Lockout Threshold vs Temperature 2.6 2.4 Switch Current Limit vs Temperature 2.0 1.8 Current Limit (A) UVLO Threshold (V) 2.2 2.0 1.8 1.6 -50 -25 0 25 50 75 100 125 Temperature ( C) 1.6 1.4 1.2 VSHDN/SS = 3V 1.0 -50 -25 0 25 50 75 100 125 Temperature ( C) Switch Saturation Voltage vs Switch Current 400 125 C 300 VCESAT (mV) VIN Quiescent Current vs Temperature 0.80 VIN Current (mA) 25 C 0.75 200 0.70 100 -40 C 0.65 VFB = 1.5V 0 0.0 0.5 1.0 1.5 2.0 Switch Current (A) 0.60 -50 -25 0 25 50 75 100 125 Temperature ( C) 2007 Semtech Corp. 6 www.semtech.com SC4503 POWER MANAGEMENT Typical Characteristics (Cont.) Shutdown Pin Current vs Shutdown Pin Voltage 70 Shutdown Pin Current ( A) Shutdown Pin Current vs Shutdown Pin Voltage 50 Shutdown Pin Current ( A) 60 50 40 30 20 10 0 0 5 10 85 C 25 C -40 C 40 -40 C 30 25 C 20 10 85 C 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 15 20 Shutdown Pin Voltage (V) Shutdown Pin Voltage (V) VIN Quiescent Current vs Shutdown Pin Voltage 1000 VIN = 3V 800 VFB = 1.5V 1.5 Shutdown Pin Thresholds vs Temperature SHDN Thresholds (V) Switching 1.0 VIN Current ( A) 600 400 200 0 0.0 125 C 25 C 0.5 Shutting Down To IIN < 1A -40 C 0.0 0.5 1.0 1.5 2.0 -50 -25 0 25 50 75 100 125 Shutdown Pin Voltage (V) Temperature ( C) Switch Current Limit vs Shutdown Pin Voltage 2.5 D = 50% 2.0 Switch Current Limit vs Shutdown Pin Voltage 2.5 D = 80% 2.0 Current limit (A) 1.5 1.0 0.5 0.0 1.2 -40 C 25 C 85 C Current limit (A) 1.5 1.0 0.5 0.0 -40 C 25 C 85 C 1.4 1.6 1.8 2.0 1.2 1.4 1.6 1.8 2.0 Shutdown Pin Voltage (V) Shutdown Pin Voltage (V) 2007 Semtech Corp. 7 www.semtech.com SC4503 POWER MANAGEMENT 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 Q3 conduction. Q3 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-compensating ramp and fed into the modulating ramp input of the PWM comparator. The latch is set and Q3 conduction is terminated when the modulating ramp intersects the error amplifier (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 Q3. Due to separate pulsewidth 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 feedback control system. In the inner current loop the EA output controls the peak inductor current. In the outer loop, the error amplifier regulates the output voltage. The double reactive poles of the output LC filter 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 SHDN SS pin enables the voltage reference. The signal "REF NOT READY" does not go low until VIN exceeds its under-voltage lockout threshold (typically 2.2V). Assume that an external resistor is placed between the IN and the SHDN SS pins during startup. The voltage reference is enabled when the SHDN SS voltage rises to 0.9V. Before VIN reaches 2.2V, "REF NOT READY" is high. Q2 turns on and the Zener diode Z1 loosely regulates the SHDN SS voltage to 1V (above the reference enabling voltage). The optional external resistor limits the current drawn during under-voltage lockout. clamped by D1 and Q1, follows the voltage at the SHDN SS pin. The input inductor current, which is in turn controlled by the error amplifier output, also ramps up gradually. Soft-starting the SC4503 in this manner eliminates high input current and output overshoot. Under fault condition (VIN < 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 R1 and R2 with its center tap tied to the FB pin (Figure 3) sets the output voltage. = - VOUT (1) R1 25nA 3 SC4503 FB R2 Figure 3. R1- R2 Divider Sets the Output Voltage The input bias current of the error amplifier will introduce an error of: =- * ( )* (2) The percentage error of a VOUT = 5V converter with R1 = 100k and R2 = 301k is =- * ( )* =- When VIN exceeds 2.2V, "REF NOT READY" goes low. Q2 turns off, releasing SHDN SS. If an external capacitor is connected from the SHDN SS pin to the ground, the SHDN SS voltage will ramp up slowly. The error amplifier output, which is 2007 Semtech Corp. 8 This error is much less than the ratio tolerance resulting from the use of 1% resistors in the divider string. www.semtech.com SC4503 POWER MANAGEMENT Applications Information (Cont.) Duty Cycle The duty cycle D of a boost converter in continuous-conduction mode (CCM) is: - = - + + where ILIM is the switch current limit. It is worth noting that IOUTMAX is directly proportional to the ratio and that switching losses are neglected in its (3) derivation. Equation (4) therefore over-estimates the maximum output current, however it is a useful first-order approximation. Using VCESAT = 0.3V, VD = 0.5V and ILIM =1.4A in (3) and (4), the maximum output current for three VIN and VOUT combinations are tabulated (Table 1). VIN (V) 3.3 3.3 5 VOUT (V) 12 5 12 D 0.754 0.423 0.615 IOUT (A) 0.34 0.80 0.53 where VCESAT is the switch saturation voltage and VD is voltage 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 flows into the switch. When the power switch is off, the inductor current flows 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 IIN Inductor Current ON 0 Diode Current OFF ON Table 1. Calculated Maximum Output Currents 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 ratio requires long switch on time and high duty Switch Current DT ON 0 OFF (1-D)T I OUT ON OFF ON cycle. If the required duty cycle is higher than the attainable 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 voltages (<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 significant 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: Figure 4. Current Waveforms in a Boost Converter a boost converter therefore depends on the converter operating 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: = - - - ( - ) (4) 2007 Semtech Corp. 9 www.semtech.com SC4503 POWER MANAGEMENT Applications Information (Cont.) = - - - (5) lessen jittery tendency but not so steep that large flux swing decreases efficiency. For continuous-conduction mode operation, inductor ripple current IL between 0.35A and 0.6A is a good compromise. Setting IL = 0.43A, VD = 0.5V and f = 1.3MHz in (7), = - = - Assuming that the voltage of a nearly discharged Li-ion cell is 2.6V. Using VD=0.5V, VCESAT=0.3V and D=0.86 in (5), < - - * - = + + (8) where L is in H. Transient headroom requirement further reduces the maximum achievable output voltage to below 16V. Minimum Controllable On-Time The operating duty cycle of a boost converter decreases as VIN approaches VOUT. 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 amplifier 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 IL of a boost converter in continuous-conduction mode is Equation (7) shows that for a given VOUT, IL is the highest ( + ) . If V varies over a wide range, then when = IN 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 = in continuous-conduction mode is limited by the maximum duty cycle DMAX: < - = - = = ( - ) (6) where f is the switching frequency and L is the inductance. Substituting (3) into (6) and neglecting VCESAT, = - Higher voltage conversion ratios can be achieved by operating the boost converter in full-time discontinuous-conV duction mode (DCM). Define R = OUT as the equivalent IOUT output load resistance. The following inequalities must be satisfied for DCM operation: < (7) and, - (9) + In current-mode control, the slope of the modulating (sensed switch current) ramp should be steep enough to 2007 Semtech Corp. 10 = < (10) www.semtech.com SC4503 POWER MANAGEMENT Applications Information (Cont.) Switch on duty ratio in DCM is given by, When the switch is turned on, the output capacitor supplies the load current IOUT (Figure 4). The output ripple voltage due to charging and discharging of the output capacitor is therefore: = - (11) Higher input current ripples and lower output current are the drawbacks of DCM operation. Input Capacitor = (13) For most applications, a 10-22F ceramic capacitor is sufThe input current in a boost converter is the inductor cur- ficient for output filtering. It is worth noting that the output rent, which is continuous with low RMS current ripples. A ripple voltage due to discharging of a 10F ceramic capaci2.2-4.7F ceramic input capacitor is adequate for most tor (13) is higher than that due to its ESR. applications. Rectifying Diode Output Capacitor For high efficiency, Schottky barrier diodes should be used Both ceramic and low ESR tantalum capacitors can be as rectifying diodes for the SC4503. These diodes should used as output filtering capacitors. Multi-layer ceramic have an average forward current rating at least equal to the capacitors, due to their extremely low ESR (<5m), are output current and a reverse blocking voltage of at least the best choice. Use ceramic capacitors with stable a few volts higher than the output voltage. For switching temperature and voltage characteristics. One may be regulators operating at low duty cycles (i.e. low output tempted to use Z5U and Y5V ceramic capacitors for output voltage to input voltage conversion ratios), it is beneficial filtering because of their high capacitance density and to use rectifying diodes with somewhat higher average cursmall sizes. However these types of capacitors have high rent ratings (thus lower forward voltages). This is because temperature and high voltage coefficients. For example, the diode conduction interval is much longer than that of the capacitance of a Z5U capacitor can drop below 60% the transistor. Converter efficiency will be improved if the of its room temperature value at -25C and 90C. X5R voltage drop across the diode is lower. ceramic capacitors, which have stable temperature and voltage coefficients, are the preferred type. The rectifying diodes should be placed close to the SW pin of the SC4503 to minimize ringing due to trace inducThe diode current waveform in Figure 4 is discontinuous tance. Surface-mount equivalents of 1N5817 and 1N5818, with high ripple-content. Unlike a buck converter in which MBRM120, MBR0520L, ZHCS400, 10BQ015 and equivathe inductor ripple current IL determines the output ripple lent are suitable. voltage. The output ripple voltage of a boost regulator is much higher and is determined by the absolute inductor Shutdown and Soft-Start current. Decreasing the inductor ripple current does not reduce the output ripple voltage appreciably. The current The shutdown ( SHDN SS ) pin is a dual function pin. When flowing in the output filter capacitor is the difference driven from a logic gate with VOH>2V, the SHDN SS pin between the diode current and the output current. This functions as an on/off input to the SC4503. When the shutdown pin is below 2V, it clamps the error amplifier capacitor current has a RMS value of: output to and reduces the switch current limit. Connecting RSS and CSS to the SHDN SS pin (Figure 5) slows - (12) the voltage rise at the pin during start-up. This forces the peak inductor current (hence the input current) to follow a If a tantalum capacitor is used, then its ripple current rating slow ramp, thus achieving soft-start. in addition to its ESR will need to be considered. 2007 Semtech Corp. 11 www.semtech.com SC4503 POWER MANAGEMENT Applications Information (Cont.) The minimum SHDN SS voltage for switching is 1.4V. The graph "Switch Current Limit vs. Shutdown Pin Voltage" in the "Typical Characteristics" shows that the SHDN SS pin voltage needs to be at least 2V for the SC4503 to deliver its rated power. The effect of the SHDN SS voltage on the SC4503 is analog between 1.4V and 2V. Within this range the switch current limit is determined not by ILIM but instead by the PWM signal path (see Figure 2). Moreover it varies with duty cycle and the shutdown pin voltage. Pulling the SHDN SS 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 SHDN SS 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 RSS. RSS limits the current drawn by the SC4503 internal IN VOH > 2V VOL < 0.4V SC4503 RLIM SHDN/SS VIN End of Soft-start VSHDN/SS > 2V RSS IN SC4503 SHDN/SS CSS (a) (b) End of Soft-start VSHDN/SS > 2V VOL < 0.4V RSS ISHDN/SS CSS IN SC4503 SHDN/SS 1.7V < VOH < 2V VOL 0 VIN RSS DSS ISHDN/SS CSS IN SC4503 SHDN/SS CMDSH-3 (c) (d) VIN End of Soft-start VSHDN/SS > 2V RSS IN SC4503 SHDN/SS VIN VOH > VIN 1N4148 IN SC4502 SHDN/SS RSS CSS CSS (e) (f) Figure 5. Methods of Driving the Shutdown Pin and Soft-starting the SC4503 (a) Directly Driven from a Logic Gate. RLIM 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 < VOH < 2V), (e) Driven from an Open-collector NPN Transistor with Soft-start and (f) Driven from a Logic Gate (whose VOH > VIN) with Soft-start. 2007 Semtech Corp. 12 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 VOH 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, CSS is charged by the difference between the RSS current and the shutdown pin current, . In steady state, the voltage drop across RSS reduces the shutdown pin voltage according to the following equation: Output filter pole, =- =- =- and = , Compensating zero, Right half plane (RHP) zero, (-) . I V IN POWER STAGE C4 R1 OUT V OUT = - (14) + RC RO CC 1.252V VOLTAGE REFERENCE R2 FB ESR C2 R In order for the SC4503 to achieve its rated switch current, must be greater than 2V in steady state. This puts an upper limit on RSS for a given enable voltage VEN (= voltage applied to RSS). The maximum specified is = 50A with (see "Electrical Characteristics"). The largest RSS can be found using (14): < - COMP Gm RO is the equivalent output resistance of the error amplifier Figure 6. Simplified Equivalent Model of a Boost Converter The poles p1, p2 and the RHP zero z2 all increase phase shift in the loop response. For stable operation, the overall loop gain should cross 0dB with -20dB/decade slope. Due to the presence of the RHP zero, the 0dB crossover . The internal frequency should not be more than compensating zero z1 provides phase boost beyond p2. In general the converter is more stable with widely spaced filter pole p2 and the RHP zero z2. The RHP zero moves to low frequency when either the duty-cycle D or the output current IOUT increases. It is beneficial to use small inductors and larger output capacitors especially when operating at high ratios. 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 and switch current limit with SHDN SS pin voltage and temperature are shown in the "Typical Characteristics". Shutdown pin current decreases as temperature increases. also decreases as Switch current limit at a given temperature rises. Lower shutdown pin current flowing through RSS at high temperature results in higher shutdown pin voltage. However reduction in switch current limit (at a given ) 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, A feed-forward capacitor C4 is needed for stability. The value of C4 can be determined empirically by observing the inductor current and the output voltage during load transient. and , C4 is Starting with a value between 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. 13 www.semtech.com =- , 2007 Semtech Corp. SC4503 POWER MANAGEMENT Applications Information (Cont.) Figures 7(a)-7(c) show the effects of different values of inductance and feed-forward capacitance on transient responses. In a battery-operated system if C4 is optimized for the minimum VIN and the maximum load step, the converter will be stable over the entire input voltage range. VOUT 0.5V/div Board Layout Considerations In a step-up switching regulator, the output filter 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 filter 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. IL1 0.5A/div 40s/div (a) L1 = 5.6H and C4 = 2.2pF VOUT 0.5V/div VOUT D1 L1 VIN IL1 0.5A/div R1 C4 C2 SW JP C1 U1 R2 40s/div (b) L1 = 5.6H and C4 = 3.3pF FB C3 R3 SHDN/SS GND VOUT 0.5V/div Figure 8. Suggested PCB Layout for the SC4503. IL1 0.5A/div 40s/div (c) L1 = 3.3H and C4 = 2.7pF Figure 7. Different inductances and feed-forward capacitances affect the load transient responses of the 3.3V to 12V step-up converter in Figure 10(a). IOUT is switched between 90mA and 280mA. 2007 Semtech Corp. 14 www.semtech.com SC4503 POWER MANAGEMENT Typical Application Circuits 5V L1 10H D1 ZHCS400 R3 54.9k C1 4.7F 5 IN SC4503 4 SHDN/SS GND C3 56nF 2 FB 3 1 SW + 24V _ D2 MM5Z24VT1 C4 220pF R4 301k C2 0.22F C5 22nF R1 63.4 R2 63.4 L1: Murata LQH32C C1: Murata GRM219R60J475K Figure 9. Driving Two 6 White LED Strings from 5V. Zener diode D2 protects the converter from over-voltage damage when both LED strings become open. 2007 Semtech Corp. 15 www.semtech.com SC4503 POWER MANAGEMENT Typical Application Circuits VIN 3.3V R3 15k C1 2.2F 5 IN L1 2.7H 1 SW SC4503 4 C3 56nF SHDN/SS GND 2 FB 3 D1 10BQ015 C4 2.2pF R1 866k VOUT 12V C2 4.7F R2 100k L1: Coiltronics LD1 C1: Murata GRM188R61A225K C2: Murata GRM21BR61C475K Figure 10(a). 3.3V to 12V Boost Converter with Soft-start Efficiency vs Load Current 95 90 85 Efficiency (%) 1.3MHz 80 75 70 65 60 55 50 0.001 0.010 VOUT = 12V 40s/div 0.100 1.000 Load Current (A) Upper Trace : Output Voltage, AC Coupled, 0.5V/div Lower Trace : Input Inductor Current, 0.5A/div Figure 10(b). Efficiency vs Load Current Figure 10(c). Load Transient Response of the Circuit in Figure 10(a). IOUT is switched between 90mA and 280mA 16 www.semtech.com 2007 Semtech Corp. SC4503 POWER MANAGEMENT Typical Application Circuits 2.6 - 4.2V 3.3V ON L1 1.5H 5 IN R3 15k SC4503 4 SHDN/SS GND 2 FB 3 1 SW D1 10BQ015 C4 10pF R1 187k VOUT 5V Efficiency vs Load Current 95 90 85 VIN = 4.2V OFF < 0.4V 1-CELL LI-ION C1 4.7F C2 10F Efficiency (%) 80 75 70 65 60 55 VOUT = 5V 1.3MHz VIN = 3.6V VIN = 2.6V C3 56nF R2 60.4k L1: TDK VLF4012AT C1: Murata GRM188R60J475K C2: Murata GRM21BR60J106K Figure 11(a). Single Li-ion Cell to 5V Boost Converter 50 0.001 0.010 0.100 1.000 Load Current (A) Figure 11(b). Efficiency of the Li-ion Cell to 5V Boost Converter VIN = 2.6V VIN = 4.2V 40s/div Upper Trace : Output Voltage, AC Coupled, 0.2V/div Lower Trace : Inductor Current, 0.5A/div 40s/div Upper Trace : Output Voltage, AC Coupled, 0.2V/div Lower Trace : Inductor Current, 0.5A/div Figure 11(c). Load Transient Response. IOUT is switched between 0.1A and 0.5A Figure 11(d). Load Transient Response. IOUT is switched between 0.15A and 0.9A 2007 Semtech Corp. 17 www.semtech.com SC4503 POWER MANAGEMENT Typical Application Circuits L1 3.3H R3 8.06k 1-CELL LI-ION C1 1F 4 5 IN SC4503 SHDN/SS GND 2 FB 3 1 SW C5 2.2F D1 10BQ015 L2 3.3H C4 15pF R1 412k C2 10F R2 249k VOUT 3.3V, 0.45A 2.6 - 4.2V C3 0.22F L1 and L2: Coiltronics DRQ73-3R3 C1: Murata GRM188R61A105K C2: Murata GRM21BR60J106K C5: Murata GRM188R61A225K Figure 12(a). Single Li-ion Cell to 3.3V SEPIC Converter. Efficiency vs Load Current 85 80 75 70 Efficiency (%) VOUT = 3.3V VIN = 3.6V 65 60 55 50 45 40 35 30 0.001 0.010 VIN = 2.6V VIN = 3.6V VIN = 4.2V 40s/div Upper Trace : Output Voltage, AC Coupled, 0.2V/div Lower Trace : Input Inductor Current, 0.2A/div 0.100 1.000 Load Current (A) Figure 12(b). Efficiency vs Load Current Figure 12(c). Load Transient Response of the Circuit in Figure 12(a). IOUT is switched between 100mA and 500mA 18 www.semtech.com 2007 Semtech Corp. SC4503 POWER MANAGEMENT Typical Application Circuits D2 D3 D4 D5 OUT2 26V (10mA) C8 1F C5 0.1F C6 0.1F C7 0.1F 3.3V L1 4.7H 5 3.3V ON < 0.4V IN SC4503 R3 4 SHDN/SS GND C3 56nF 2 FB 3 1 SW D1 10BQ015 C4 12pF R1 309k OUT1 9V (0.3A) OFF C2 4.7F X 2 RUN 17.8k C1 4.7F C9 0.1F R2 49.9k D7 OUT3 -8.5V (10mA) C10 1F D6 D2 - D7 : BAT54S L1 : Sumida CDC5D23B-4R7M C2: Murata GRM21BR61C475K C1: Murata GRM188R61A105K Figure 13(a). Triple-Output TFT Power Supply with Soft-Start CH4 CH1 CH2 CH3 400s/div CH1 : OUT1 Voltage, 5V/div CH2 : OUT2 Voltage, 20V/div CH3 : OUT3 Voltage, 5V/div CH4 : RUN Voltage, 5V/div Figure 13(b). TFT Power Supply Start-up Transient as the RUN Voltage is Stepped from 0 to 3.3V 2007 Semtech Corp. 19 40s/div Upper Trace : Output Voltage, AC Coupled, 0.5V/div Lower Trace : Inductor Current, 0.5A/div Figure 13(c). Load Transient Response. IOUT1 is switched between 50mA and 350mA www.semtech.com SC4503 POWER MANAGEMENT EVB Schematic 12VOUT D1 SS13 L1 4.7uH 5VIN U1 R1 0R R2 432K C2 N.P. C3 10uF 8 7 6 C4 15pF 5 R5 49.9K R4 0R FB SHDN/SS 4 N.C. GND GND SW SW VIN 1 2 3 R3 47K C1 10uF OFF/ON SC4503_MLPD C5 100nF JP1 L1 4.7uH D1 SS13 1 SW VIN 5 12VOUT 5VIN R1 0R C4 15pF R2 432K C2 N.P. C3 10uF 2 GND R3 47K C1 10uF 3 R4 0R R5 49.9K FB SHDN 4 OFF/ON U1 SC4503 C5 100n JP1 2007 Semtech Corp. 20 www.semtech.com SC4503 POWER MANAGEMENT Outline Drawing - TSOT-23 DIMENSIONS INCHES MILLIMETERS MIN NOM MAX MIN NOM MAX .000 .028 .012 .003 .110 .060 .039 .004 .035 .020 .008 .118 .067 0.00 0.70 0.30 0.08 2.80 1.50 1.00 0.10 0.90 0.50 0.20 3.00 1.70 A e1 N E1 1 ccc C 2X N/2 TIPS B D aaa C A2 SEATING PLANE C A1 bxN bbb C A-B D A 2 E D DIM A A1 A2 b c D E1 E e e1 L L1 N 01 aaa bbb ccc 2X E/2 e .114 .063 .110 BSC .037 BSC .075 BSC .012 .018 .024 (.024) 5 0 8 .004 .008 .010 2.90 1.60 2.80 BSC 0.95 BSC 1.90 BSC 0.30 0.45 0.60 (0.60) 5 0 8 0.10 0.20 0.25 H GAGE PLANE 0.25 L (L1) DETAIL SEE DETAIL c 01 A A SIDE VIEW NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. DATUMS -A- AND -B- TO BE DETERMINED AT DATUM PLANE -H3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. 4. REFERENCE JEDEC STD MO-193, VARIATION AB. Land Pattern - TSOT-23 X DIM (C) G Y P Z C G P X Y Z DIMENSIONS INCHES MILLIMETERS (.087) .031 .037 .024 .055 .141 (2.20) 0.80 0.95 0.60 1.40 3.60 NOTES: 1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. 2007 Semtech Corp. 21 www.semtech.com SC4503 POWER MANAGEMENT Outline Drawing - 8 Lead 2X2mm MLPD-W A D B DIM PIN 1 INDICATOR (LASER MARK) E A aaa C A1 A2 C SEATING PLANE A A1 A2 b D D1 E E1 e L N aaa bbb .028 .030 .031 .000 .001 .002 (.008) .007 .010 .012 .075 .079 .083 .059 .063 .067 .075 .079 .083 .031 .035 .039 .020 BSC .008 .012 .016 8 .003 .003 DIMENSIONS INCHES MILLIMETERS MIN NOM MAX MIN NOM MAX 0.70 0.75 0.80 0.00 0.02 0.05 (0.20) 0.18 0.25 0.30 1.90 2.00 2.10 1.50 1.60 1.70 1.90 2.00 2.10 0.80 0.90 1.00 0.50 BSC 0.20 0.30 0.40 8 0.08 0.08 D1 1 E/2 LxN E1 2 N bxN e e/2 D/2 bbb CAB NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS THE TERMINALS. Land Pattern - 8 Lead 2X2mm MLPD-W Contact Information Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805) 498-2111 Fax: (805) 498-3804 www.semtech.com 2007 Semtech Corp. 22 www.semtech.com |
Price & Availability of SC4503TSKTRT
 |
|
|
|
|
All Rights Reserved © IC-ON-LINE 2003 - 2022 |
| [Add Bookmark] [Contact Us] [Link exchange] [Privacy policy] |
|
Mirror Sites : [www.datasheet.hk]
[www.maxim4u.com] [www.ic-on-line.cn]
[www.ic-on-line.com] [www.ic-on-line.net]
[www.alldatasheet.com.cn]
[www.gdcy.com]
[www.gdcy.net] |