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ADS122C04: device is coming out of low power mode

Viktorija Cecil
Mastermind 18491 points
Part Number: ADS122C04

Team, 

My customer is noticing that ADS122C04 is coming out of deep sleep mode when there is any I2C activity, as opposed to when the start of conversion is initiated. 

Any ideas what could be happening?

Thanks

Viktorija

  • 0
    TI__Guru** 113765 points
    Hi Viktorija,

    The POWERDOWN command turns off all analog circuitry. The digital portion will also go to low power until I2C becomes active. When the I2C bus becomes active the ADS122C04 needs to wake the digital portion to determine if the device is being addressed. Note that the digital current/power information in the electrical characteristics table on page 7 of the datasheet is listed with 'I2C Not Active'.

    The analog power should not change until the START/SYNC command is issued.

    Best regards,
    Bob B
  • 0 in reply to Bob Benjamin
    TI__Mastermind 18491 points
    Bob, thank you for a quick reply. Follow up question:

    That does make sense but I seem to be getting a higher current draw then just the digital section waking up after power down mode (from i2c activity).
    The digital only shows a Max of about 100uA but I'm seeing a full 320 uA draw.

    Question
    Is there something more I can do to reduce this current draw or is best practice to simply put ads122c04 in power down mode after every i2c transaction ?
    I guess there is a part of me wondering if in power down mode and i2c traffic - why wouldn't the ads122c04 automatically go back to power down mode if realizes not being addressed (not target of i2c data) ?

    Thanks
    Viktorija
  • 0 in reply to Viktorija Cecil
    TI__Guru** 113765 points
    Hi Viktorija,

    I will have to check with the designer to see what internal actions take place when the I2C bus becomes active. In the meantime, could you get me the configuration register settings being used on the ADS122C04?

    Thanks,
    Bob B
  • 0 in reply to Bob Benjamin
    TI__Mastermind 18491 points
    At this point it is just after a reset so all default :)
  • 0 in reply to Viktorija Cecil
    TI__Guru** 113765 points
    Hi Viktorija,

    One other question. Is the current being measured AVDD, DVDD or a combination of both?

    Thanks,
    Bob B
  • 0 in reply to Bob Benjamin
    TI__Mastermind 18491 points
    Both are being measured as a combination. I can't resolve if analog or digital section.
  • 0 in reply to Viktorija Cecil
    TI__Guru** 113765 points
    Hi Viktorija,

    The current draw is much larger than I would expect, especially for low power mode (as opposed to POWERDOWN) where the device is in the default of single-shot mode. Depending on how the device is connected and where the current is being measured, it is possible that DRDY (being open drain) is pulling some of the current if the DRDY state is low and there is a pull-up resistor connected to the DVDD supply.

    Let's say the supply is 3.3V and the pullup resistor is 10k Ohm. The current just from DRDY will be 330uA. If low power operation is required, any pullup on DRDY should be in the range of 100k to 470k Ohm to limit this current when DRDY is low.

    I'm still waiting to hear back from the designer.

    Best regards,
    Bob B
  • 0 in reply to Bob Benjamin
    TI__Mastermind 18491 points
    Bob,
    Just received a confirmation from my customer:
    • The issue is NOT with the TI ADS122C04 chip
    • It seems my I2C bus master – if I2C transaction error is keeping SCL (clock) LOW (until a valid I2C transaction) – which is generating the unwanted 360uA

    Please consider this case closed and thank you so much for your support!

    Thanks
    Viktorija