• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 45 subscribers
  • Views 186 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS124S08 nDRDY pin doesn't go low every time

Jake Baldwin
Prodigy 20 points
Part Number: ADS124S08

I'm having an issue with the nDRDY pin not going low after every conversion. I'm taking a single sample at the 2.5 SPS interval (~406ms for the sample). It seems that sometimes my firmware doesn't detect a low nDRDY signal within 800ms, at which time I timeout and report an error. I can verify this behavior on a scope. I have a few questions:

1) Is there an errata for this chip that may describe something like this? I wasn't able to find one.

2) I'm using the START command (the START/SYNC pin is tied to ground) to kick off a conversion. How do I tell if the conversion actually started? I can check to see if nDRDY is high after the START command but that doesn't really tell me much because nDRDY is also high after startup.

3) My application requires very very low power so I have the whole chip on switched power so I'm cutting power to it between conversion cycles. After I apply power, the firmware waits for the the power supply to settle, then waits 5ms for the ADS124S08 to boot, then sends a WAKEUP followed right away by a RESET command, then waits 5ms, then sets ups up the registers for my conversion (and reads back to verify) and starts the conversion with a START command. Is there anything wrong with this sequence?

4) Is the nDRDY pin a push-pull output? Or should I use a pull-up or pull-down on the line?

Incidentally I'm also seeing the same behavior in continuous mode. Not sure if this is relavent or not.

  • 0
    TI__Guru** 112725 points

    Hi Jake,

    Here are my responses:

    1) There are no errata for the ADS124S08.

    2) There is no particular method other than monitoring DRDY to see if a conversion took place.

    3) You may be sending to many commands.  The ADS124S08 will remain in a reset state until all supplies are at nominal operating voltage.  Once the supplies are nominal, the POR signal within the ADS124S08 will release.  There is no need to send a WAKEUP or an additional RESET command.  If you write the registers and read them back successfully, the the ADC should start converting on the START command.  I would highly recommend using the CS signal if you are not currently do so.  Toggling the CS between commands will reset the SPI bus in case there was a communication issue.

    4) Yes, the DRDY output is always active push-pull.

    Best regards,

    Bob B