Using PWM Output as a Digital-to-Analog Converter on a TMS320F280x (Rev. A)

This application report presents a method for utilizing the on-chip pulse width modulated (PWM) signal generators on the TMS320F280x™ family of digital signal controllers as a digital-to-analog converter (DAC). The method involves analog low-pass filtering the PWM signal to remove high frequency components, leaving only the low-frequency content. Theoretical and experimental results are presented to quantify the achievable bit resolution and bandwidth, which depend upon the analog low-pass filter employed, the PWM frequency, and the DSP operating frequency. When coupled with a second order passive RLC filter, the hi-resolution PWM module on the TMS320F280x device is seen capable of providing greater than 9 bits of DAC resolution with 100 kHz bandwidth. Alternately, 50 kHz DAC bandwidth is possible with better than 10 bits of resolution. These resolutions and bandwidths make the PWM/DAC a legitimate lower cost alternative to dedicated off-chip DACs in TMS320F280x based systems.