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ADS1291 power up requirements question and status of the analog digital pins

user4616852
Prodigy 40 points
Other Parts Discussed in Thread: ADS1291, ADS1292ECG-FE

The datasheet states:

"POWER-UP SEQUENCING

Before device power-up, all digital and analog inputs must be low. At the time of power-up, all of these signals
should remain low until the power supplies have stabilized".

However, in my application, we plan to tie RESET high, and use the opcode for reset. Also, we need to tie CLKSEL high since we are using internal CLK. We were also advised to tie IN2P and IN2N high since we are not using them.  All of these signals are high (or go hi as the power rail comes high) which technically violate the power up sequencing requirement above.

Is it OK to have these signals tied high?

  • 0
    TI__Guru**** 180961 points
    Hi user4616852,

    Welcome to our E2E forum!

    With the ADS1291 signals you described as being tied to a voltage rail (they go hi as the power rail comes high) is fine. The absolute MAX ratings (see page 2 for digital and analog inputs to DVdd and AVdd/ss) let you know that those signals have to be within 300mV of their respective voltage rails.

    You should be fine with your proposed connection scheme. If you can find a spare GPIO to control the PDWN/RESET input, you might find that helpfull in debugging when it comes to that point.
  • 0 in reply to Tom Hendrick
    Prodigy 40 points
    Hi Tom,
    Thanks for the reply. Can you please let me know what could happen if the GPIOs that control some of the digital lines happen to be high before the ADS1291 chip is powered?
    We have a situation now that the chips are getting very hot and in 3 cases, they have died on us. I'm now wondering if this could explain what might have been happening. We started experiencing this when we moved away from GPIO control of the START and RESET and instead tied them to GND and DVDD respectively. We haven't had a chance yet to fully debug what's happening. What we are doing currently is using TI demo board (ADS1292ECG-FE Demonstration Kit), powering it up with a USB power source, and disconnecting the control lines from U7 (by removing R23, R26,R27, R44, R45, R54, R55) and fly wiring them to our own MCU (with its own power supplies). So there might be a slight mismatch between the ADS_DVDD and our MCU's 3.3V (but certainly less than 300mV).

    Not only we have managed to kill 3 demo boards so far, but we are also observing some strangeness where we use a battery pack to power the system (rather than an AC USB charger or the PC/laptop USB port) to try to keep the main level noise down. However, while the rest of our system works fine from the battery pack (typical battery packs you use to charge your cellphone on the go), but the TI dev board shuts down intermittently (where the green LED indicator also goes off) while the rest of our system powered from the same battery pack is OK. We also don't know yet why this is happening with the TI dev board. Any ideas?

    --Arash
  • 0 in reply to user4616852
    TI__Guru**** 180961 points
    Hi Arash,

    Without knowing what your USB source is or what your own MCU schematic looks like, first thing I would do is to check your ground wiring.

    Verify the ground wiring from your USB source, to the ADS1292EVM, to your MCU. Once your are sure you have a good solid ground connection, bring power up from a current controlled source - like a bench top power supply - so that you can verify the correct power levels while limiting current that might damage components if something is mis-wired.