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www.semtech.com SC2603A Simple PWM Boost Converter In Small SOT23-6 Package POWER MANAGEMENT Description Features
Applications
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 compo - nents. The small device footprint allows for compact circuit design. 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. The SC2603A operates at a fixed frequency of 200kHz, providing an optimum compromise between efficiency, external component size, and cost. Typical Application Circuit Revision: May 8, 2007 Low cost / small size Input voltage range: 5V to 30V 200kHz switching frequency Up to 95% efficiency % reference voltage accuracy Typical 800mA PWM gate drive capability Internal compensation Over current protection SOT23-6 package is fully WEEE and RoHS compliant Portable Devices Flat Panel TV TV Set Top Box Auxiliary Supplies Peripheral Card Supplies Industrial Power Supply High Density DC/DC Conversion Figure : 2V to 25V/A Boost Conveter + C1 VOUT Optional 1 2 VIN SC2603A 1 2 4VIN EN/SS FB GND CS GATE R6C4 + C2 Enable
2 2007 Semtech Corp. www.semtech.com SC2603A POWER MANAGEMENT Absolute Maximum Rating
Electrical Characteristics
Note: (1) Mounting pad has to be larger than one square inch on two sided printed circuit board with minimum 1 ounce copper 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 Input Voltage 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 Maximum Junction Temperature 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 Unless specified: VIN = 2V, VO = 25V; TA = TJ = -40°C to 25°C Parameter Symbols Conditions Min Typ Max Units General VIN Supply Voltage VIN 4.5 16 V VIN UVLO Threshold VUVLO VIN ramping up 4.2 4.5 V VIN UVLO Hysteresis VHYS 400 mV VIN Supply Current Current into VIN pin during switching 6.0 9.0 mA VIN Shutdown Current EN/SS=Low 5.0 6.0 mA Error Amplifier Reference Voltage VFB 1.225 1.250 1.275 V Feedback Bias Current IFB VIN = 12V, VFB = VEN/SS 2.0 8.0 µA Error Amplifier Gain(1) 105 V/V Oscillator Oscillator Frequency TA = 25 °C 190 200 210 kHz Oscillator Frequency Shift VFB < VREF /2 50 kHz Maximum Duty Cycle 90 95 % Internal Ramp Peak VR_PEAK 1.4 V Internal Ramp Valley VR_VALLEY 0.4 V
3 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 ISS 60 µA Enable/Soft Start Threshold Pull down below this level to disable PWM Switch gate 0.09 0.12 V Switch Current Limit Current Limit Threshold CS 65 73 80 mV Note: (1) Guaranteed by design
4 2007 Semtech Corp. www.semtech.com SC2603A POWER MANAGEMENT Pin Configurations Ordering Information TOP VIEW 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. Part Number Package SC2603ASKTRT(1,2) SOT23-6 SC2603AEVB Evaluation Board Pin Pin Name Pin Function
1 FB Error amplifier inverted input
2 GND Device ground
3 EN/SS Enable / Soft Start Pin
4 GATE PWM gate driver output
5 VIN Device input voltage
6 CS Current Sense input
(6 Pin SOT-23) Block Diagram Figure 2: SC2603A Function Diagram GND 5 CS6 VIN2 EN/SS FB GATE VIN FB GATE CS UVLO GND PWM EN/SS 70mV Current Limit VIN UV S Q R OSCILLATOR 1.25V REF 1.25V REF 25K
5 2007 Semtech Corp. www.semtech.com SC2603A POWER MANAGEMENT Applications Information Theory of Operation 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. 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. Setting the Output Voltage As shown in Fig.1, an external resistive divider R2 and R4 with its center tap tied to the FB pin sets the output volt - age. Soft-Start Soft-start prevents a DC-DC converter from drawing exces- sive 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 00mV 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. Under Voltage Lockout 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. MAXIN OUT D V V Maximum Duty Cycle The maximum duty cycle, D max defines the upper limit of power conversion ratio Clamping Diode D2 at Vin Pin Since the Vin pin of the SC2603A is rated at 20V, when the supply voltage is higher than 6V, 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 5V. Over Current Protection (OCP) 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. 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. ) 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. A RC filter at the CS pin is necessary to filter out noise to ensure accurate sensing. The value of the sensing resistor can be calculated by the following equation: Rs = 70mV/Ipeak −= V25. VRR OUT
Figure 3. Current Waveforms differentials must be understood and minimized. to not unnecessarily compromise ground plane integrity. in more reliable gate switching signals. output capacitor should be a wide trace or copper region. GND be returned to a ground inside the Cin, Q1, D1 loop.
7 2007 Semtech Corp. www.semtech.com SC2603A POWER MANAGEMENT Applications Information (Cont.) Layout diagram for the SC2603A Figure 4: SC2603A Layout Diagram Note: Heavy lines indicate the critical loop carrying high pulsating current. The inductance of the loop needs to be minimized. Vout 12VIN Cout 2.2 0.1uF 0.1uF SC2603A GND VIN5 CS6 GATE FB Rb Ra Rs EN/SS Cin
8 2007 Semtech Corp. www.semtech.com SC2603A POWER MANAGEMENT Applications Information (Cont.) Typical application schematic with 12V input and 24V/1A output Bill of materials Item Quantity Reference Part Vendor 1 1 C1 220uF/16V Panasonic 2 1 C2 330uF/35V Nichicon, VR 3 2 C3,C10 1uF/16V Vishay 4 1 C4 0.1uF Vishay 5 1 C5 120pF Vishay 6 1 C11 1uF/50V Vishay 7 1 Cc 56nF Vishay 8 1 D1 CMSH2-40M Central Semi 9 1 L1 33uH/5.1A (HC8-330) Coiltronics 10 1 Q1 IRF7821 IR 11 1 R1 2R2 Vishay 12 1 R2 226k Vishay 13 1 R4 12.4k Vishay 14 1 R5 1k Vishay 15 1 R6 20m Vishay 16 1 Rc 2.3k Vishay 17 1 U1 SC2603A Semtech 0.1uF 120pF SC2603A 3 4 6FB GND EN/SS GATE VIN CS + C1 220uF Cc 56nF 12V INPUT 20m 24V/1A OUTPUT 12.4k Rc 2.3k 226k + C2 330uF 33uH 1 2 C10 1uF R1 2R2 CMSH2-40M IRF7821 C11 1uF 1uF
2007 Semtech Corp. www.semtech.com SC2603A POWER MANAGEMENT Semtech Corporation Power Management Products Division
200 Flynn Road, Camarillo, CA 302
Phone: (805)48-2 FAX (805)48-3804 Contact Information Land Pattern - SOT23-6 Outline Drawing - SOT23-6 .110 BSC .037 BSC DETAIL aaa C SEATING ccc C 2X N/2 TIPS 2X E/2 SEE DETAIL AA2 bxN A .008 1 2 N E .060 .114 .063 .122 .010 - A 0.20 1.60 3.10
2.80 BSC
0.95 BSC
.069 1.50 2.90 .020 0.25 1.75 0.50- EI L (L1) c 0.25 PLANE GAGE H 2.80.110 bbb C A-B D .008 .004 .012 .003 (.024) .018 .035 .000 .035 .045 0.10 0.20 10° 0° - 10° 1.15 (0.60) 0.45.024 .009 0.30 0.08 .057 .051 .006 0.00 .90 0.90 0.22 0.60 0.15 1.45 1.30 1.90 BSC.075 BSC A e1 D e B C PLANE D DATUMS AND TO BE DETERMINED AT DATUM PLANE CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS3. OR GATE BURRS. NOTES: 2. -A- -B- -H- SIDE VIEW NOM INCHES DIMENSIONS aaa bbb ccc N DIM c e L E D b A MIN MILLIMETERS MAX MIN NOM MAX DIMENSIONS INCHES Y Z DIM G P X C MILLIMETERS P (C) Z Y G .043 .141 .055 (.098) .037 .024 1.40 (2.50) 0.95 0.60 1.10 3.60 X DIMENSIONS INCHES Y Z DIM G P X C MILLIMETERS THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. NOTES: