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TMS320F28388D: Same ADC module acquisition 12 and 16 bit

Part Number: TMS320F28388D

Hello,

We are currently facing an issue with sampling ADC channels on module C and D. For each module, we are sampling 1x channel at 12 bit resolution and 2x channels in differential mode at 16 bits.

There are 2 problems:

1) For module C, the channel sampled at 12 bits returns values in 16 bit...my guess is that the converter for the module is set to 16 bit regardless of which resolution we chose for the specific channel. The input voltage is read correctly and the rescaling the integer value to 16 bit solve the issue. 

2) For module D, the ADC sampled at 12 bit returns incorrect results even after rescaling...the input voltage is read incorrectly and the signal responds slowly to the changes in input voltage.

FYI:

1) The acquisition from all ADCs is triggered by the same ePWM trigger at 20 kHz

2) ADC clock frequency = 40 Mhz

3) We are using programming the target in Simulink 

Any suggestion?

thanks

Francesco 

  • Need to make a correction to point 1) above...also the module C works incorrectly and the measured voltage is wrong by 0.2 V

  • Hi Francesco,

    Each ADC module in the F28388D can be programmed independently however operating one as 12-bit and another as 16-bit mode results in asynchronous mode of operation.  The timings for 12-bit and 16-bit operations are different and this will result with the conversion phase signals coupling with the sampling phase.  Please see the technical reference manual for details.

    Would be best to operate all ADC modules in the same mode to avoid asynchronous operation that results in severely degraded performance.

    Regards,

    Joseph