RE: Having Trouble Getting the ADS1259 to work at 5V DVDD

Gordon Cowen

Other Parts Discussed in Thread: PGA280, ADS1259

The ADS1259 and PGA280 work great as a pair with a 3.3V DVDD. Much better noise performance than the previous AD parts.

However, with another design using these parts I have only 5V at the moment. When I transferred the design it does not work. The VREFOUT from the ADC collapses from 2.5V after a few seconds (configuration?) and the START input to the ADC oscillates. Is this a problem with the voltage levels?

Design 1 Good PGA280 VSN/P +10V, VSOP 5VA, DVDD 3.3V, ADS1259 AVDD 5VA, DVDD 3.3V

Design 2 Bad PGA280 VSN/P +14V, VSOP 5VA, DVDD 5V, ADS1259 AVDD 5VA, DVDD 5V

The datasheets imply both these setups are OK.

over 9 years ago

0 Christopher Hall over 9 years ago

TI__Mastermind 44550 points

Hi Gordon,

Welcome to the TI E2E Forums!

Would you be able to share a schematic? (You can email it to me at pa_deltasigma_apps@ti.com instead of posting it to the forum).

It sounds like their may be a grounding issue... It does not make much sense for the ADS1259 voltage reference to be affected by increasing the digital supply voltage.

Also, I'm unsure what could possibly drive an oscillation on the START pin, because this is GPIO signal that takes on a high or low value - there should be no positive feedback loop to cause an oscillation (EXCEPT, and I mean a big except, perhaps a feedback loop could be made through the power supplies).

Have you probed all of your power supplies to make sure they are coming up correctly and settling to a stable value?

The only other thing that I think might cause odd behavior would be some sort of latch-up caused by the power-up sequencing. How are you currently powering on the circuit? Do you have any input signals applied before the supplies ramp up?

Best Regards,
Chris

0 Gordon Cowen over 9 years ago in reply to Christopher Hall

Prodigy 50 points

Hi Chris, I have sent the info you requested via email.

0 Christopher Hall over 9 years ago in reply to Gordon Cowen

TI__Mastermind 44550 points

Hi Gordon,

I just replied via email. Let me know if applying 5V DVDD to the PGA fixes the issue!

Best Regards,
Chris

0 Gordon Cowen over 9 years ago in reply to Christopher Hall

Prodigy 50 points

The schematic was not accurate as there is no 3.3V on the prototype board.

I have both PGA and ADC DVDD connected to +5V.

0 Christopher Hall over 9 years ago in reply to Gordon Cowen

TI__Mastermind 44550 points

Hi Gordon,

Hmm...bummer, I thought I had it figured out :)

Would you be able to take a picture of the proto-board and send it to me? Maybe there is something else that is not matching up with the schematic, or maybe there are parasitic elements in your circuit.

Best Regards,
Chris

0 Gordon Cowen over 9 years ago in reply to Christopher Hall

Prodigy 50 points

I have emailed you a jpg of the PCB. Would the Gerber help or is another format better?

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RE: Having Trouble Getting the ADS1259 to work at 5V DVDD