SC4503TSKTRT

SC4503 1.3MHz Step-Up Switching Regulator with 1.4A Switch POWER MANAGEMENT Description Features 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. ‹ 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 (< 1μA) ‹ Low Profile 5-Lead TSOT-23 and 8-Lead 2X2mm MLPD-W packages ‹ Fully WEEE and RohS compliant The SC4503 is available in low-profile 5-lead TSOT-23 and 8-lead 2X2mm MLPD-W packages. The SC4503’s low shutdown current (< 1μA), high frequency operation and small size make it suitable for portable applications. Applications ‹ Local DC-DC Converters ‹ TFT Bias Supplies ‹ XDSL Power Supplies ‹ Medical Equipment ‹ Digital Cameras ‹ Portable Devices ‹ White LED Drivers Typical TypicalApplication ApplicationCircuit Circuit D1 5V 4.7µH 5 C1 1µF 90 C4 15pF SW R1 432k SC4503 OFF ON 4 SHDN/SS FB 95 12V, 0.5A 10BQ015 1 IN Efficiency vs Load Current VOUT C2 4.7µF 3 GND 2 1.3MHz 85 R2 49.9k Efficiency (%) L1 VIN 80 75 70 65 60 VOUT = 12V 55 50 0.001 C1: Murata GRM188R61A105K C2: Murata GRM21BR61C475K L1: Sumida CDC5D23B-4R7 0.100 1.000 Load Current (A) Figure 1(b). Efficiency of the 5V to 12V Boost Converter Figure 1(a). 5V to 12V Boost Converter May 4, 2007 0.010 1 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 Symbol Maximum Supply Voltage VIN -0.3 to 20 SW Voltage VSW -0.3 to 34 FB Voltages VFB -0.3 to VIN +0.3 VSHDN -0.3 to VIN +1 Thermal Resistance Junction to Ambient (TSOT - 23) θ JA 191* °C/W Thermal Resistance Junction to Ambient (2X2 mm MLPD-W) θ JA 78* °C/W Maximum Junction Temperature TJ 150 Storage Temperature Range TSTG -65 to +150 Lead Temperature (Soldering)10 sec (TSOT - 23) TLEAD 260 Peak IR Reflow Temperature (2X2mm MLPD-W) TIR 260 ESD 2000 SHDN/SS Voltage ESD Rating (Human Body Model) Units V °C 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, -40°C < TA = TJ < 85°C Parameter Conditions Min Under-Voltage Lockout Threshold Typ Max 2.2 2.5 Maximum Operating Voltage 20 Feedback Voltage Feedback Line Voltage Regulation 1.225 2.5V < VIN < 20V 1.15 V 1.275 0.02 FB Pin Bias Current Switching Frequency 1.250 Units %/V -25 -50 nA 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 ISW = 1.4A 260 430 mV Switch Leakage Current VSW = 5V 0.01 1 µA VSHDN/SS = 2V, VFB = 1.5V (not switching) 0.8 1.1 mA VSHDN/SS = 0 0.01 1 µA VIN Quiescent Supply Current VIN Supply Current in Shutdown  2007 Semtech Corp. 2 www.semtech.com SC4503 POWER MANAGEMENT Electrical Characteristics (Cont.) Unless specified: VIN = VSHDN/SS = 3V, -40°C < TA = TJ < 85°C Parameter Conditions SHDN/SS Switching Threshold Min VFB = 0V Typ Max Units 1.4 Shutdown Input High Voltage V 2 V Shutdown Input Low Voltage 0.4 SHDN/SS Pin Bias Current VSHDN/SS = 2V 22 50 VSHDN/SS = 1.8V 20 45 VSHDN/SS = 0V µA 0.1 Thermal Shutdown Temperature 155 Thermal Shutdown Hysteresis 10 °C Pin Configuration - TSOT - 23 Ordering Information Top View SW 1 GND 2 FB 3 5 IN Device(1,2) Top Mark Package SC4503TSKTRT BH00 TSOT-23 SC4503EVB 4 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. SHDN/SS 5-LEAD TSOT-23 Pin Descriptions - TSOT -23 Pin Pin Name 1 SW 2 GND 3 FB 4 5 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. 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  2007 Semtech Corp. Power Supply Pin. Bypassed with capacitor close to the pin. 3 www.semtech.com SC4503 POWER MANAGEMENT Pin Configuration - 2mm X 2mm MLPD Ordering Information Top View Device(1,2) SW 1 8 NC SW 2 7 GND IN 3 6 GND SHDN/SS 4 5 FB SC4503WLTRT SC4503_MLPD EVB Top Mark Package E00 2mmX2mm MLPD-W 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. 8-LEAD 2X2mm MLPD-W Pin Descriptions - 2X2mm MLPD-W Pin Pin Name 1,2 SW 3 IN 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. 4 SHDN/SS 5 FB 6,7 GND Ground. Tie to ground plane. 8 N.C. No Connection. EDP  2007 Semtech Corp. The inverting input of the error amplifier. Tie to an external resistive divider to set the output voltage. Solder to the ground plane of the PCB. 4 www.semtech.com SC4503 POWER MANAGEMENT Block Diagram IN 5 SW 1 + Z1 1V - REF NOT READY Q2 SHDN/SS 4 TJ > 155°°C VOLTAGE THERMAL REFERENCE SHUTDOWN 1.25V + EA - FB 2 CLK - R + S PWM Q3 Q D1 ILIM Q1 + I-LIMIT R SENSE Σ OSCILLATOR + + SLOPE COMP + ISEN 2 GND Figure 2. SC4503 Block Diagram  2007 Semtech Corp. 5 www.semtech.com SC4503 POWER MANAGEMENT Typical Characteristics Switching Frequency vs Temperature FB Voltage vs Temperature 1.30 1.5 1.4 Frequency (MHz) FB Voltage (V) 1.25 1.20 1.15 1.2 1.1 1.10 1.0 -50 -25 0 25 50 75 100 125 -50 -25 0 25 50 75 100 125 Temperature (°C) Temperature (°C) VIN Under-voltage Lockout Threshold vs Temperature Switch Current Limit vs Temperature 2.6 2.0 2.4 1.8 Current Limit (A) UVLO Threshold (V) 1.3 2.2 2.0 1.6 1.4 1.8 1.2 1.6 1.0 VSHDN/SS = 3V -50 -25 0 25 50 75 100 125 -50 -25 0 Temperature (°C) 25 50 75 100 125 Temperature (°C) VIN Quiescent Current vs Temperature Switch Saturation Voltage vs Switch Current 400 0.80 125°C 0.75 25°C VIN Current (mA) VCESAT (mV) 300 200 100 -40°C 0.70 0.65 VFB = 1.5V 0.60 0 0.0 0.5 1.0 1.5 -50 2.0 0 25 50 75 100 125 Temperature (°C) Switch Current (A)  2007 Semtech Corp. -25 6 www.semtech.com SC4503 POWER MANAGEMENT Typical Characteristics (Cont.) Shutdown Pin Current vs Shutdown Pin Voltage Shutdown Pin Current vs Shutdown Pin Voltage 50 -40°C 60 50 Shutdown Pin Current ( µ A) Shutdown Pin Current ( µ A) 70 25°C 40 30 20 85°C 10 -40°C 0 20 10 85°C 5 10 15 0.0 20 0.5 1.0 1.5 2.0 2.5 Shutdown Pin Voltage (V) Shutdown Pin Voltage (V) VIN Quiescent Current vs Shutdown Pin Voltage Shutdown Pin Thresholds vs Temperature 1000 3.0 1.5 VIN = 3V VFB = 1.5V 600 SHDN Thresholds (V) 800 125°C 25°C 400 200 Switching 1.0 0.5 Shutting Down To IIN < 1µA -40°C 0.0 0 0.0 0.5 1.0 1.5 -50 2.0 -25 0 25 50 75 100 125 Temperature (°C) Shutdown Pin Voltage (V) Switch Current Limit vs Shutdown Pin Voltage Switch Current Limit vs Shutdown Pin Voltage 2.5 2.5 D = 50% D = 80% 2.0 Current limit (A) 2.0 Current limit (A) 25°C 30 0 0 VIN Current (µ A) 40 -40°C 1.5 85°C 25°C 1.0 -40°C 1.5 1.0 25°C 85°C 0.5 0.5 0.0 0.0 1.2 1.4 1.6 1.8 1.2 2.0  2007 Semtech Corp. 1.4 1.6 1.8 2.0 Shutdown Pin Voltage (V) Shutdown Pin Voltage (V) 7 www.semtech.com SC4503 POWER MANAGEMENT Applications Information 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. 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. 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. 9 5 = 5 §¨ 287 −  ·¸ ¹ ©  9 (1) VOUT SC4503 R1 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. 25nA 3 FB R2 Figure 3. R1- R2 Divider Sets the Output Voltage The input bias current of the error amplifier will introduce an error of: 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 ( ) Q$ • 5°«5 •  ∆9287  =− 9287  9 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 (2) The percentage error of a VOUT = 5V converter with R1 = 100kΩ and R2 = 301kΩ is ( SHDN SS voltage to 1V (above the reference enabling voltage). The optional external resistor limits the current drawn during under-voltage lockout. ) Q$ • N°«N •  ∆9287 =− = − 9287  9 This error is much less than the ratio tolerance resulting from the use of 1% resistors in the divider string. 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 www.semtech.com SC4503 POWER MANAGEMENT Applications Information (Cont.) where ILIM is the switch current limit. Duty Cycle It is worth noting that IOUTMAX is directly proportional to the 9 ratio ,1 and that switching losses are neglected in its 9287 derivation. Equation (4) therefore over-estimates the maximum output current, however it is a useful first-order approximation. The duty cycle D of a boost converter in continuous-conduction mode (CCM) is: 9,1 9287 + 9' '= 9  − &(6$7 9287 + 9' − (3) 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). 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 ON OFF ON Switch Current OFF ON I OUT ON OFF 3.3 12 0.754 0.34 3.3 5 0.423 0.80 5 12 0.615 0.53 ON 0 Note: dropout can occur when operating at low input voltages (