SLAAE21 April 2021 DAC43701 , DAC43701-Q1 , DAC53701 , DAC53701-Q1
Key Input Parameter | Key Output Signal | Recommended Device |
---|---|---|
0-V to 5.5-V analog input, programmable triangular waveform | Pulse-width modulation (PWM) output | DAC53701, DAC43701, DAC53701-Q1, DAC43701-Q1 |
Objective: Translate digital inputs to a variable duty cycle PWM output.
This design uses a buffered voltage output smart DAC to decode two general-purpose inputs (GPIs) into a constant-frequency PWM output with four selectable duty cycle levels. This design can be expanded to increase the number of GPIs and duty cycle levels. The 8-bit DAC43701 and 10-bit DAC53701 have an integrated continuous waveform generator (CWG) that can produce square, triangular, and sawtooth waveforms. In this design, the integrated buffer acts as a comparator and a triangle waveform generated by the CWG acts as the threshold for the comparator. The DAC43701 and DAC53701 integrated buffer has an exposed feedback path via the feedback pin (FB) which acts as the voltage input to the comparator. The comparator generates a PWM output with the same frequency as the triangle wave, and a duty cycle dependent on the FB input. All register settings can be saved using the non-volatile memory (NVM) on the DAC43701 and DAC53701 meaning that the devices can be used without a processor, even after a power cycle. This circuit can be used in applications such as automotive rear lights, rear light fault indication, and fault communication in factory automation and control designs.
The equation becomes:
This is rounded to 819d and 205d to give a VTRIANGLE_HIGH of 3.999V and VTRIANGLE_LOW of 1V.
SLEW_RATE and CODE_STEP are selected in the GENERAL_CONFIG Register. A CODE_STEP of 8 least significant bits (LSBs) and SLEW_RATE of 32μs per code step can be selected to produce a frequency of 203.25Hz:
This schematic is used for the following simulations of the DAC53701 GPI to PWM.
The simulation shows the DAC53701 output responding to the changes on GPI1 and GPI2. The DAC_POS value reflects the triangle wave generated by the CWG. The value at VFB changes with the voltage levels on the GPI pins and adjusts the duty cycle of the PWM output.