ADS1294R: VREFP under voltage

Alex Leffell

Part Number: ADS1294R

Hello,

I am bringing up a new board using the ADS1294R. However, upon enabling the internal reference and setting it to 2.4 V (I'm using a 3V analog supply), the VREFP pin goes to the correct voltage for only a few seconds (the exact time varies). See the picture attached. The first rise is after resetting the board. The second one is after I reprogram register 3 to 0b11001100. The pin has capacitors as recommended in the datasheet. Any thoughts on why this is happening?

Thanks

over 4 years ago

0 Alex Leffell over 4 years ago

Prodigy 95 points

A few other notes: The current board has the BGA option. On another board with the 1298 QFP I don't have this issue.

0 Alexander Smith over 4 years ago in reply to Alex Leffell

TI__Mastermind 47595 points

Hi Alex,

I assume that your software is the same for both boards, so I don't think this is necessarily the issue,butt the BIOFAQ has a good post on verifying correct functionality for your device: https://e2e.ti.com/support/data-converters/f/73/p/772058/2855202

It would be good to verify that your VCAP voltages are correct - it may be that there is a timing issue in your power-up routine with a different layout.

This behavior (and how the voltage settles to ~100mV) makes me think could be an unintended short somewhere.

Do you see this behavior on all of your BGA ADS1294R boards or just the one?

0 Ryan Andrews over 4 years ago in reply to Alexander Smith

TI__Guru 57296 points

Hi Alex L.,

Along the lines of what Alex. S. was saying, you might want to verify that registers are being read/written correctly after the power-up routine. After you write to the device and enable the internal reference, can you confirm that you can read both the Device ID and the CONFIG3 registers?

If the registers look correct, you might have a short on the board somewhere. Can you measure the impedance between VREFP and VREFN when power is not applied to the board?

Regards,

0 Alex Leffell over 4 years ago in reply to Ryan Andrews

Prodigy 95 points

I measure 15kohm without power applied, but I also measure that on a board that seems to be working. VCAP4 is also ~20mV, other VCAP voltages are fine. I'm having the BGA's Xray'd, Just wanted to check if there are other possible causes.

0 Alexander Smith over 4 years ago in reply to Alex Leffell

TI__Mastermind 47595 points

Hi Alex,

15kohm sounds about right for a correctly working board. Ryan was simply asking since a measurement of 0ohms (or very low) would indicate a short circuit.

0 Alex Leffell over 4 years ago in reply to Alexander Smith

Prodigy 95 points

If it isn't a short any thoughts on what else it could be? I only see this behavior on some of my boards.

0 Alexander Smith over 4 years ago in reply to Alex Leffell

TI__Mastermind 47595 points

Hi Alex,

Like Ryan and I mentioned in previous posts - it could also be an issue with your power-up routine.

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ADS1294R: VREFP under voltage