UCC21750: Resolution of the analog to PWM Converter

Matthias,

The isolated APWM channel duty cycle can effectively be considered as a completely linear relationship with VIN based on the equation in the datasheet.

We don't quote a resolution and it is not as useful for this APWM because so the minimum step size of VIN is miniscule and is determined by the internal comparator metastability. It is completely different structure from something like a SAR or sigma delta.

The minimum step size of the APWM output is more useful (change of duty cycle), we quote it as 0.1% based on our measurements.

Compared with a standalone ADC, there are going to be some difference when compared with something like Isolated sigma-delta which is commonly seen in the applications like inverter, motor drive, etc.

Isolated sigma delta can be used to be get a higher degree of accuracy or speed than +/- 1.5% of APWM, and directly converts output to digital. The APWM output must be low-pass filtered before it is converted by another ADC. such as a discrete ADC or internal ADC in the controller. There is a limitation of the bandwidth of the APWM (10kHz) as well.

APWM channel helps to reduce BOM cost and area for measurements that don't need extreme accuracy or speed, like DC bus voltage, temperature monitoring, etc. So it isn't a catch-all for EVERYthing that requires isolated sensing, like phase current measurement, position monitoring, etc.

As far as further information, we have a Report on accuracy of the APWM, I think it could be helpful

If this has answered your question, Please let me know by pressing the green button, and let us know if you have any more questions.

Best

Dimitri

Matthias, Youre welcome!

please dont hesitate to reach out if you have any questions in the future.

best

dimitri