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  • PIC12F1501 Based Buck Converter

  • Created: Mar 14, 2017

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This reference design features an asynchronous buck converter that is based on the PIC12F1501 microcontroller. It can accept an input voltage from 8VDC up to 16VDC and outputs a 5V voltage level with a maximum of 2A output current. The design utilizes the PIC12F1501’s 10-bit ADCs, 5-bit DAC, comparator, numerically controlled oscillator, and complementary waveform generator. It utilizes 452 out of 1024 words of the PIC12F1501 program ROM and 31 out of 64 bytes data RAM.

The design uses a PIC12F1501 microcontroller with an MCP1416 IC MOSFET driver, NTMS4177PR2G MOSFET, inductor-capacitor network, and other components to step down the 8-16VDC input from a battery or 8-16VDC power supply. The voltage regulation and overcurrent limit is done by programming the PIC12F1501 microcontroller. The design uses the PIC12F1501 numerically controlled oscillator peripheral to generate a fixed on time, variable frequency control signal for the buck converter. The “on time” is fixed to 2us and the duty cycle is limited to about 90% at 450kHz. The numerically controlled oscillator frequency step is about 16Hz using a 16MHz clock source. A control loop modifies the numerically controlled oscillator frequency to regulate the converter output. The decisions are made based on the ADC values read from the output voltage resistor divider (R1 and R2) and the output current shunt (R3). Since only one control loop is running for both voltage and current regulation, a special function decides on each update which of the two needs to be regulated. In normal operating conditions, the control loop tries to match the output voltage to the reference. If the output current goes over the limit, the loop tries to match the output current to the maximum-allowed value by reducing the output voltage.

This PIC12F1501 based buck converter uses digital proportional control for output voltage regulation with only 4kHz update rate. Since the update rate is not so fast, the system responds slowly to abrupt changes in the input voltage and the load. For this reason, the output voltage is clamped by a very fast comparator-based, overvoltage protection mechanism. The PIC12F1501 peripheral configuration allows 15 bits of duty-cycle resolution for the transistor control signal, which enables very fine control of output voltage and current. This PIC12F1501 based buck converter can be used in applications such as battery charger, LED driver, thermoelectric cell driver, programmable bias generator, etc.