TMS320F280049: TMS320F280049: "DAC to ADC loopback Check" vs "Opens/Shorts Detection Circuit for ADC"

Hi Davide,

See below for the updated description of the ADCDACLOOPBACK register from the F28003x TRM. The description will be updated in the next release of the F28004x TRM.

Davide Dentoni said:

"Setting this bit to 1, will override the CHSEL specification for the ADC. ADC would sample DACA output irrespective of the value of CHSEL."

What does it mean exactly ?

Setting this bit to 1 for the ADC will cause it to sample the internal output of CMPSS1 DACL rather than the ADC pin.

Davide Dentoni said:

Setting ENLB2ADCC to 1 (together with KEY = 0xA5A5) creates an internal connection between DACA and the ADCC peripheral, so that I can read the DACA value from any ADCC ADCRESULTx register (when properly configured) ?

You will still need to configure SOC. The only difference is the CHSEL field of the SOC is ignored and the SOC will sample CMPSS1 DACL.

Davide Dentoni said:

If so, can you confirm that with this strategy just the functionality of Sample+Hold circuit is tested, therefore reading a single ADCRESULTx is enough to know about the integrity of the ADCx S+H (reading more channels is useless) ?

Correct, just the S/H is tested. This is an internal loopback connection so the ADC pins are bypassed.

Davide Dentoni said:

On the other hand, OSDETECT circuitry is useful to detect situations of Open/Short inputs (but in this case I'm not testing microcontroller internal hardware, rather external connections) and in this case it is necessary to apply the strategy explained at par. 13.9 of TRM to all the channels that I need to guarantee?

Yes, you would use OSDETECT to detect pins faults such as open and shorts.