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ADS1220: ADS1220 - minimizing power consumption

Dan Ringger
Intellectual 1790 points
Part Number: ADS1220

I’m looking at the ADS1220.   Our application will use a single load cell and varying sample rates.   For much of the devices life the sample rate will be quite low ( 1 sample every 30seconds to 1 minute ).   Keeping Power consumption low for this application is critical.   What’s the best way to handle such a low sample rate?    Should I turn the ADS-1220 off?   Does it have a standby/sleep?

Thank you

  • 0
    TI__Mastermind 44550 points

    Hi Dan,

    The ADS1220 provides a duty-cycle mode and a power-down mode. Duty-cycle mode runs at about 5 SPS, much faster than what you're asking for, so I would recommend putting the ADS1220 into power-down mode to conserve power and waking it up as often as you want to measure the bridge.

    Also, you'll want to take advantage of the low-side switch (see Figure 82 for a load cell circuit example) to turn off the excitation current while you're not measuring the bridge.

  • 0 in reply to Christopher Hall
    TI__Intellectual 1790 points

    Thx Chris.  How quickly could I go from power off, turn it on,   take a measurement, and then turn it back off again?  Is there a single sample mode or do I put it in a high sample rate mode and just put it in and out of power down?  I’m trying to put together an approximate power budget.

  • 0 in reply to Dan Ringger
    TI__Mastermind 20845 points

    Hi Dan,

    please apologize for the delayed response. I try to help Chris out here as I defined the ADS1220.

    The ADS1220 supports both a single-shot conversion mode as well as a continuous-conversion mode.
    From power-down mode you can directly start conversions using the START/SYNC command. Section '8.3.5.Output Data Rates' explains any additional overhead times you should consider for you calculation.

    However there are a few things to consider when using single-shot conversion mode and potentially the integrated low-side switch of ADS1220 to power the bridge down.
    If you are using single-shot conversion mode you should make sure the analog input signal to the ADC (bridge output signal) is fully settled before the conversion starts. This will be especially tricky when you use the internal low-side switch of ADS1220 to control the excitation of the bridge.
    In power-down mode the switch is open, so that the bridge is not powered. When you send the START/SYNC command, the switch closes and the ADC start sampling right away. But in this case the output signal of the bridge has most likely not settled yet. How long it will take for the bridge signal to settle is hard for me to say. That is something you would probably have to try out.

    Assuming the bridge excitation is controlled externally then a sequence could look like the following:
    - Bridge powered off, ADS1220 in power-down mode
    - Enable bridge excitation
    - Wait for the bridge output to settle.
    - Send START/SYNC command to ADS1220
    - Wait for conversion to complete (/DRDY falling edge)
    - Read conversion result
    - Send POWERDOWN command to ADS1220
    - Disable bridge excitation

    In case the internal low-side switch is used to control the bridge then I would alter the sequence in the following way (assuming we are using single-shot conversion mode):
    - ADS1220 in power-down mode (low-side switch open = bridge excitation disabled)
    - Send START/SYNC command (this will close the low-side switch and thus enable the bridge excitation)
    - Wait for the bridge output to settle (disregard the /DRDY falling signal)
    - Send START/SYNC command
    - Wait for conversion to complete (/DRDY falling edge)
    - Read conversion result
    - Send POWERDOWN command to ADS1220 (this will open the low-side switch and thus disable the bridge excitation)

    Another note. If you really want to save every uA, then the best thing to do would be to completely cut the power to the ADS1220. The great thing about the ADS1220 is that it starts/wakes up super quick. The only downside of cutting the power is that you will have to write the configuration registers at every power-up again. At the most this are four registers. But customers who use the ADS1220 in battery powered applications and only measure once per minute typically do that.

    Regards,