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TMS320F280049: PGA output and ADC/CMPSS

Wayne Huang
Genius 16705 points
Part Number: TMS320F280049


Champs,

I am asking this for our customers.

On Fig 5-36 PGA Block Diagram of F28004x datasheet (sprs945d), I have some questions.

1. If we enable both PGAEN and FILTRESSEL, is it PGA_OUT or PGA_OF that "To ADC and CMPSS" gets internally?

2. Take pin 36 on the 100-pin F280049 as an example. Is PGA2 output (PGA_OUT or PGA_OF) only to ADC-A4 or ADC B8 or CMPSS-2 High or CMPSS-2 Low internally?

If we want to connect PGA2 to another ADC pin (say, pin ADC-A1), we should use PGA_OF and wire pin36 to ADC-A1 (pin 22)?

Is our understanding correct?

Wayne Huang

  • 0
    TI__Mastermind 28275 points

    Hi Wayne,

    Every PGA has 2 outputs, PGA_OUT and PGA_OF. They both go to the ADC and CMPSS however, PGA_OF comes out on a pin but PGA_OUT does not. The PGAs, ADCs and CMPSSs are grouped. Internal connections are only possible for PGAs, ADCs and CMPSS within a group. If you would like to mix and match across groups, you would need to use a jumper wire. This is of course only possible for signals that come out on a pin.

    Also keep in mind that if you do the mix and match across groups, you actually lose ADC channels. I'll give you an example; Take PGA6_OF for instance. PGA6_OF and A8 are on the same pin so ADCA can sample PGA6_OF on A8 without any other connections. Now let's say you want to sample PGA6_OF on A6 rather than on A8. Since PGA6_OF and A6 are not in the same group, you would have to jumper PGA6_OF to A6. This will work but you can't use A8 to sample anything else because it's tied to PGA6_OF even though you aren't using A8 to sample PGA6_OF. This is a bit wordy but i hope it explains it.

    So to answer your questions:

    1. Yes, if you enable PGAEN and FILTRESSEL, PGA_OUT and PGA_OF go to the ADC and CMPSS internally.

    2. Yes, PGA2_OF only goes to  A4, B8 and the CMPSS mux options on that line. See explanation above.