SC2603ASKTRT

SC2603A Simple PWM Boost Converter In Small SOT23-6 Package POWER MANAGEMENT Description Features The SC2603A is a versatile, low-cost, voltage-mode PWM controller designed for DC/DC power supply applications. A simple, fixed-voltage boost regulator can be implemented using the SC2603A with a minimum of external components. The small device footprint allows for compact circuit design.  Low cost / small size  Input voltage range: 5V to 30V  200kHz switching frequency  Up to 95% efficiency  1% reference voltage accuracy  Typical 800mA PWM gate drive capability  Internal compensation  Over current protection  SOT23-6 package is fully WEEE and RoHS compliant SC2603A features include a temperature compensated voltage reference, triangle wave oscillator, current limit comparator, frequency shift over-current protection, and an internally compensated error amplifier. Pulse by pulse current limiting is implemented by sensing the differential voltage across an external resistor, or an appropriately sized PC board trace. Applications  Portable Devices  Flat Panel TV  TV Set Top Box  Auxiliary Supplies  Peripheral Card Supplies  Industrial Power Supply  High Density DC/DC Conversion The SC2603A operates at a fixed frequency of 200kHz, providing an optimum compromise between efficiency, external component size, and cost. Typical Application Circuit L1 VIN 1 R1 C3 + D1 C1 + Enable 5 3 C4 C2 Q1 D2 Optional VOUT 2 1 R2 U1 VIN EN/SS FB GATE CS GND 4 R5 6 2 C5 R6 R4 SC2603A Figure 1: 12V to 25V/1A Boost Conveter Revision: May 8, 2007  www.semtech.com SC2603A POWER MANAGEMENT Absolute Maximum Rating 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 implied. Exposure to Absolute Maximum rated conditions for extended periods of time may affect device reliability. Parameter Symbol Maximum Units VIN to GND -0.3 to 20 V GATE Pin Voltage VGATE -0.3 to 20 V EN/SS Pin Voltage VEN/SS -0.3 to 7 V FB Pin Voltage VFB -0.3 to 7 V Thermal Resistance Junction to Ambient(1) θ JA 165 °C/W Thermal Resistance Junction to Case θ JC 102 °C/W TJ 150 °C Storage Temperature Range TSTG -45 to +150 °C Lead Temperature (Soldering)10 sec TLEAD 300 °C ESD Rating (Human Body Model) ESD 2 kV Input Voltage Maximum Junction Temperature Note: (1) Mounting pad has to be larger than one square inch on two sided printed circuit board with minimum 1 ounce copper Electrical Characteristics Unless specified: VIN = 12V, VO = 25V; TA = TJ = -40°C to 125°C Parameter Symbols Conditions Min Typ Max Units 16 V 4.5 V General VIN Supply Voltage VIN VIN UVLO Threshold VUVLO VIN UVLO Hysteresis VHYS VIN Supply Current VIN Shutdown Current 4.5 VIN ramping up 4.2 400 mV Current into VIN pin during switching 6.0 9.0 mA EN/SS=Low 5.0 6.0 mA 1.250 1.275 V 2.0 8.0 µA Error Amplifier Reference Voltage VFB Feedback Bias Current IFB 1.225 VIN = 12V, VFB = VEN/SS Error Amplifier Gain(1) 105 V/V Oscillator Oscillator Frequency TA = 25 °C Oscillator Frequency Shift 190 VFB < VREF /2 Maximum Duty Cycle 90 200 210 kHz 50 kHz 95 % Internal Ramp Peak VR_PEAK 1.4 V Internal Ramp Valley VR_VALLEY 0.4 V  2007 Semtech Corp.  www.semtech.com SC2603A POWER MANAGEMENT Electrical Characteristics (Cont.) Parameter Symbols Conditions Min Typ Max Units Regulation Load Regulation IO = 0.1A to 1A 0.3 0.5 % Line Regulation VIN = 5V to 15V, Io = 0.1A 0.5 1.0 % PWM Gate Drive GATE Source Current VIN = 12V, CGATE = 10nF 0.5 0.8 1.1 A GATE Sink Current VIN = 12V, CGATE = 10nF 0.5 0.8 1.1 A Enable and Soft Start Soft Start Charge Current Enable/Soft Start Threshold ISS 60 µA V Pull down below this level to disable PWM Switch gate 0.09 0.12 CS 65 73 Switch Current Limit Current Limit Threshold 80 mV Note: (1) Guaranteed by design  2007 Semtech Corp.  www.semtech.com SC2603A POWER MANAGEMENT Ordering Information Pin Configurations Part Number Package SC2603ASKTRT(1,2) SOT23-6 SC2603AEVB Evaluation Board TOP VIEW FB 1 6 CS GND 2 5 VIN EN/SS 3 4 GATE Notes: (1) Only available in tape and reel packaging. A reel contains 3000 devices. (2) Lead free product. This product is fully WEEE and RoHS compliant. (6 Pin SOT-23) Pin Descriptions Pin Pin Name Pin Function 1 FB 2 GND 3 EN/SS Enable / Soft Start Pin 4 GATE PWM gate driver output 5 VIN Device input voltage 6 CS Current Sense input Error amplifier inverted input Device ground Block Diagram OSCILLATOR VIN S PWM FB R GATE Q GND 25K Current Limit CS EN/SS UV VIN 1.25V REF 1.25V REF 70mV UVLO Figure 2: SC2603A Function Diagram  2007 Semtech Corp.  www.semtech.com SC2603A POWER MANAGEMENT Applications Information Theory of Operation Maximum Duty Cycle The SC2603A is a versatile, low-cost, voltage-mode PWM controller designed for DC/DC power supply applications. In normal condition, the SC2603A operates at a fixed 200kHz. One exception is that when the FB pin voltage drops to one half, the frequency will be shifted to one fourth of 200kHz. The maximum duty cycle, Dmax defines the upper limit of power conversion ratio VOUT  = VIN  − D MAX SC2603A features include a temperature compensated voltage reference, triangle wave oscillator, current limit comparator, frequency shift over-current protection, and an internally compensated error amplifier. Pulse by pulse current limiting is implemented by sensing the differential voltage across an external resistor, or an appropriately sized PC board trace. Clamping Diode D2 at Vin Pin Since the Vin pin of the SC2603A is rated at 20V, when the supply voltage is higher than 16V, a Zener diode D2 is required to limit the SC2603A supply voltage, as shown in Fig.1. The clamping voltage of D2 has to be not higher than 15V. Setting the Output Voltage Over Current Protection (OCP) As shown in Fig.1, an external resistive divider R2 and R4 with its center tap tied to the FB pin sets the output voltage. The over-current protection is implemented by a sensing resistor and an internal current-limit comparator with a threshold of 70mV. In each switching cycle, if the switching current through the sensing resistor causing the voltage at the CS pin reaches 70mV, the SC2603A will immediately turn the gate pulse off to limit the current through the power switch.  V  R 2 = R 4  OUT −    . 25 V   Soft-Start The figure below shows the current waveforms run into over-current protection. At t1, the input current Iin begins to increase as the load Iout builds up until it hits the OCP threshold at t2. At t2, Vout begins to drop as Iout starts increasing toward t3 while Vin and Iin remain the same. At t3, there two events are happening. 1) Vout is at half of its regulating voltage. At this point, the internal oscillator runs into frequency shift mode and shifts the frequency to one fourth of the operating frequency. 2) The diode starts conducting current without limit causing Vin to fall due to supply current limit. Finally, Vin and Vout both drops to zero and Iin becomes the input supply current limit. Soft-start prevents a DC-DC converter from drawing excessive current from the power source during start up. If the soft-start time is made sufficiently long, then the output will enter regulation without overshoot. An external capacitor is connected from the EN/SS pin to the ground. After the part’s input voltage surpasses the UVLO, the EN/SS pin is allowed to charge its capacitor with 60µA. When 100mV is reached at the EN/SS pin, the internal comp node is at 0.4V. The SC2603A will start switching, and the converter output comes into regulation. Because the FB pin voltage follows EN/SS pin voltage, finally, the EN/SS pin voltage will be clamped at 1.25V same as the reference voltage. A RC filter at the CS pin is necessary to filter out noise to ensure accurate sensing. Under Voltage Lockout The value of the sensing resistor can be calculated by the following equation: The under voltage lockout circuit of the SC2603A assures that the Gate output remains in the off state whenever the supply voltage drops below set parameters. Lockout occurs if Vin falls below 3.8V. Normal operation resumes once Vin rises above 4.2V.  2007 Semtech Corp. Rs = 70mV/Ipeak  www.semtech.com SC2603A POWER MANAGEMENT Applications Information (Cont.) in more reliable gate switching signals. where Ipeak is the input peak current through the power MOSFET. Normal Loading SS 3) The connection between the junction of Q1, D1 and the output capacitor should be a wide trace or copper region. It should be as short as practical. Since this connection has fast voltage transitions, keeping this connection short will minimize EMI. Supply Current Limiting OCP 4) The Output Capacitor(s) (Cout) should be located as close to the load as possible, fast transient load currents are supplied by Cout only, and connections between Cout and the load must be short, wide copper areas to minimize inductance and resistance. IIN IOUT Layout Guidelines 5) The SC2603A is best placed over an isolated ground plane area. The soft-start capacitor, the Vin decoupling capacitor, and the current sensing filter capacitor should also connected to this ground pad area. This isolated ground area should be connected to the main ground by a trace that runs from the GND pin to the ground side of the output capacitor. If this is not possible, the GND pin may be connected to the ground path between the Output Capacitor and the Cin, Q1, D1 loop. Under no circumstances should GND be returned to a ground inside the Cin, Q1, D1 loop. Careful attentions to layout requirements are necessary for successful implementation of the SC2603A PWM controller. High currents switching at 200kHz are present in the application and their effect on ground plane voltage differentials must be understood and minimized. 6) Input voltage of the SC2603A should be supplied from the power rail through a 2.2~10Ω resistor, the Vin pin should be decoupled directly to GND by a 0.1µF~1µF ceramic capacitor, trace lengths should be as short as possible. 1) The high power parts of the circuit should be laid out first. A ground plane should be used. The number and position of ground plane interruptions should be such as to not unnecessarily compromise ground plane integrity. Isolated or semi-isolated areas of the ground plane may be deliberately introduced to constrain ground currents to particular areas, for example the input capacitor and bottom Schottky ground. 7) An RC low pass filter is required to filter out leading edge current spikes on the current sensing resistor. The filter capacitor needs to be very close to the CS and GND to reduce noise pickup. VOUT VIN t0 t1 t2 t3 t4 Figure 3. Current Waveforms 2) The loop formed by the output Capacitor(s) (Cout), the FET (Q1), the current sensing resistor, and the Schottky (D1) must be kept as small as possible, as shown on the layout diagram in Fig.4. This loop contains all the high current, fast transition switching. Connections should be as wide and as short as possible to minimize loop inductance. Minimizing this loop area will reduce EMI, lower ground injection currents, resulting in electrically “cleaner” grounds for the rest of the system and minimize source ringing, resulting  2007 Semtech Corp.  www.semtech.com SC2603A POWER MANAGEMENT Applications Information (Cont.) Layout diagram for the SC2603A Vout 12VIN Ra L1 D1 Cin 2.2 5 3 0.1uF Q1 SC2603A 0.1uF 6 VIN FB EN/SS GATE CS GND Rb 1 + Cout 4 Rs 2 Note: Heavy lines indicate the critical loop carrying high pulsating current. The inductance of the loop needs to be minimized. Figure 4: SC2603A Layout Diagram  2007 Semtech Corp.  www.semtech.com SC2603A POWER MANAGEMENT Applications Information (Cont.) Typical application schematic with 12V input and 24V/1A output 12V INPUT 1 + C1 220uF D1 L1 C11 1uF CMSH2-40M 33uH C10 1uF 24V/1A OUTPUT 2 R1 2R2 Q1 IRF7821 R2 226k + C2 330uF Rc 2.3k U1 1 Cc 2 3 56nF FB CS GND VIN EN/SS C4 0.1uF GATE SC2603A R5 6 R4 12.4k 1k 5 4 C3 1uF C5 120pF R6 20m Bill of materials Item Quantity Reference 1 1 C1 2 1 C2 3 2 C3,C10 4 1 C4 5 1 C5 6 1 C11 7 1 Cc 8 1 D1 9 1 L1 10 1 Q1 11 1 R1 12 1 R2 13 1 R4 14 1 R5 15 1 R6 16 1 Rc 17 1 U1  2007 Semtech Corp. Part 220uF/16V 330uF/35V 1uF/16V 0.1uF 120pF 1uF/50V 56nF CMSH2-40M 33uH/5.1A (HC8-330) IRF7821 2R2 226k 12.4k 1k 20m 2.3k SC2603A Vendor Panasonic Nichicon, VR Vishay Vishay Vishay Vishay Vishay Central Semi Coiltronics IR Vishay Vishay Vishay Vishay Vishay Vishay Semtech  www.semtech.com SC2603A POWER MANAGEMENT Outline Drawing - SOT23-6 DIM A e1 2X E/2 ccc C 2X N/2 TIPS A A1 A2 D N EI 1 b c D E1 E e e1 L L1 N 01 aaa bbb ccc E 2 e B D aaa C SEATING PLANE A2 DIMENSIONS INCHES MILLIMETERS MIN NOM MAX MIN NOM MAX .057 .035 .000 .006 .035 .045 .051 .010 .020 .003 .009 .110 .114 .122 .060 .063 .069 .110 BSC .037 BSC .075 BSC .012 .018 .024 (.024) bxN bbb 10° 0° 6 0.10 0.20 0.20 10° A H A1 C 6 .004 .008 .008 0° 1.45 0.90 0.00 0.15 .90 1.15 1.30 0.25 0.50 0.08 0.22 2.80 2.90 3.10 1.50 1.60 1.75 2.80 BSC 0.95 BSC 1.90 BSC 0.30 0.45 0.60 (0.60) C A-B D c GAGE PLANE 0.25 L (L1) SEE DETAIL A DETAIL 01 A SIDE VIEW NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. DATUMS -A- AND -B- TO BE DETERMINED AT DATUM PLANE -H- 3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. Land Pattern - SOT23-6 X DIM (C) G Z Y P C G P X Y Z DIMENSIONS INCHES MILLIMETERS (.098) .055 .037 .024 .043 .141 (2.50) 1.40 0.95 0.60 1.10 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. Contact Information Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805)498-2111 FAX (805)498-3804  2007 Semtech Corp.  www.semtech.com