TMS570LS3137 ADC power supplies

Richard Burke

Expert 1910 points

Other Parts Discussed in Thread: TMS570LS3137

Hello,

The TRM for the TMS570LS3137 states

"Both ADREFHI and ADREFLO must be chosen not to exceed the analog power supplies: VCCAD and VSSAD respectively."

So what happens if this is not the case? If ADREFHI is slightly below VCCAD, is it clipped to VCCAD?

Thanks,

Richard

over 9 years ago

0 Richard Burke over 9 years ago

Expert 1910 points

Sorry I meant to say if ADREFHI is slightly above VCCAD.

0 Sunil Oak over 9 years ago in reply to Richard Burke

TI__Mastermind 49120 points

Richard,

How much do you mean by "slightly"?

Regards,
Sunil

0 Sunil Oak over 9 years ago in reply to Sunil Oak

TI__Mastermind 49120 points

Richard,

The datasheet is fairly clear in that ADREFHI must not exceed VCCAD. This is critical in order to support the ADC electrical specifications listed in the datasheet.

We cannot provide any opinion that is different from what the datasheet states, regardless of how much ADREFHI exceeds VCCAD by.

Regards,
Sunil

0 Richard Burke over 9 years ago in reply to Sunil Oak

Expert 1910 points

Hi Sunil,

The only practical solution would therefore be to use the same supply for ADREFHI and VCCAD then?

In our current board, they use different supplies and we have observed that VCCAD is 4.875V compared with 4.995 on ADREFHI. I was therefore wondering if you could provide some guidance on what effects this might have.

Thanks,

Richard

0 Sunil Oak over 9 years ago in reply to Richard Burke

TI__Mastermind 49120 points

Hi Richard,

Yes, especially if the ADREFHI is not expected to be too much different from VCCAD (as in your case).

You start forward-biasing diodes when ADREFHI > VCCAD. At one point (not characterized, or even specified) ADREFHI starts powering the ADC and any other circuits powered by VCCAD.

Regards,
Sunil

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TMS570LS3137 ADC power supplies