TMS320F28377D: Problem with window comparator trip offset.

Fikołek

I have configured the Comparator as Window Comparator to trip when the AC current is over range. The offset of AC current sensor is constant:

Offset = 2026;

Cmpss1Regs.DACHVALS.bit.DACVAL = 2212

Cmpss1Regs.DACLVALS.bit.DACVAL = 1839

When I try to test trip using DC power supply the trip occur with about 13A offset. The trip occur below 2212 -> 2138 which means 13A difference! With the reverse polarity is the same problem.

The solution is shifting Cmpss1Regs.DACHVALS.bit.DACVAL and Cmpss1Regs.DACLVALS.bit.DACVAL to get trip in the right place but it does not satisfy me.

Why it occurs?

over 7 years ago

0 Frank Ankapong over 7 years ago

TI__Mastermind 28275 points

Hi Fikołek,

The compdac has an offset spec of -/+ 25mV. If your application requires tight trips, then you need to calibrate out the offset. Basically what this means is, for a reference voltage of 3.3V and DACVAL of 2048, the internal compdac voltage will be a value within this range: 1.625V<->1.675V (2017<->2079). You will need to figure out which voltage/DACVAL it is by manually sweeping the compdac to find it and then record that value for your application instead of the ideal 2048.

0 Fikołek over 7 years ago in reply to Frank Ankapong

Intellectual 270 points

I did almost exactly it as You described.

Thanks for explanation.

0 Frank Ankapong over 7 years ago in reply to Fikołek

TI__Mastermind 28275 points

You're welcome. Let us know if you have anymore questions.

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TMS320F28377D: Problem with window comparator trip offset.