Data Sheet 340kHz, 3A Synchronous DC-DC Buck Converter AP3503F General Description Features The AP3503F is a 340kHz fixed frequency, current Input Voltage Range: 4.5V to 18V mode, PWM synchronous buck (step-down) DC-DC Fixed 340kHz Frequency converter, capable of driving a 3A load with high High Efficiency: up to 95% efficiency, excellent line and load regulation. The Output Current: 3A device integrates N-channel power MOSFET Current Mode Control switches with low on-resistance. Current mode Built-in Over Current Protection control provides fast transient response and Built-in Thermal Shutdown Function cycle-by-cycle current limit. Built-in UVLO Function Built-in Over Voltage Protection The AP3503F employs complete protection to ensure Programmable Soft-start system security. Including output Over Voltage Protection, input Under Voltage LockOut, programmable soft-start, Over Temperature Applications Protection to safeguard the circuit. LCD TV This IC is available in PSOP-8 package. Set Top Box Portable DVD Digital Photo Frame PSOP-8 Figure 1. Package Type of AP3503F Oct. 2012 Rev. 1. 3 BCD Semiconductor Manufacturing Limited 1 Data Sheet 340kHz, 3A Synchronous DC-DC Buck Converter AP3503F Pin Configuration MP Package (PSOP-8) 8 1 2 7 3 6 4 5 Figure 2. Pin Configuration of AP3503F (Top View) Pin Description Pin Number Pin Name Function Bootstrap pin. A bootstrap capacitor is connected between the BS pin 1 BS and SW pin. The voltage across the bootstrap capacitor drives the internal high-side power MOSFET Supply power input pin. A capacitor should be connected between the 2 IN IN pin and GND pin to keep the input voltage constant Power switch output pin. This pin is connected to the inductor and 3 SW bootstrap capacitor 4 GND Ground pin Feedback pin. This pin is connected to an external resistor divider to program the system output voltage. When the FB pin voltage exceeds 5 FB 1.1V, the over voltage protection is triggered. When the FB pin voltage is below 0.3V, the oscillator frequency is lowered to realize short circuit protection Compensation pin. This pin is the output of the transconductance error amplifier and the input to the current comparator. It is used to 6 COMP compensate the control loop. Connect a series RC network from this pin to GND. In some cases, an additional capacitor from this pin to GND pin is required Control input pin. EN is a digital input that turns the regulator on or 7 EN off. Drive EN high/low to turn on/off the regulator. Pull up with 100k resistor for automatic startup Soft-start control input pin. SS controls the soft-start period. Connect a capacitor from SS to GND to set the soft-start period. A 0.1F 8 SS capacitor sets the soft-start period to 15ms. To disable the soft-start feature, leave SS unconnected EP Exposed pad. It should be connected to GND in PCB layout Oct. 2012 Rev. 1. 3 BCD Semiconductor Manufacturing Limited 2