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ADS131A04: Can I drive a bridge using the REFP pin?

adsfsadfadsfda
Prodigy 90 points
Part Number: ADS131A04

Can I use the internal reference to power a resistor bridge circuit? The bridge circuit is a very slow, less than 1 Hz, signal, and at 4 V pulls 50 uA.

I want the voltage across the bridge to be the same as the ADC reference (4 V) so that any variation or drift in the reference doesn't matter affect the reading of the bridge. I could use an external voltage reference, but if possible, I'd rather use the internal reference through the REFP pin.

The datasheet says "REFP source capability" is 100 uA, but it doesn't really give much detail about what this means. If I keep my bridge drawing less than 100 uA, does that mean I would be within spec? Will it have any negative effect on the other ADC channels? Another solution would be to use a buffer, but if I don't need to do that I don't want to. The buffer would add more places for drift to occur.

  • 0
    TI__Mastermind 45805 points

    Hi adsfsadfadsfda,

    I will look into the details and get it back to you tomorrow, thanks.

    Regards,

    Dale

  • +1 in reply to Dale Li
    TI__Mastermind 45805 points

    Hi adsfsadfadsfda,

    Thanks for your patience. An external source is recommended to power the bridge as an excitation voltage, for example,  a linear regulator. Below is an example:

    The external +5V supply can provide a power for the ADC (AVDD), also it is used as an excitation voltage to excite the bridge. This solution can bring more benefits for you, not only it is a ratiometric measurement to eliminate errors due to the noise and drift in the excitation source, more importantly this solution make it possible for you to use a six-wire bridge measurement which can eliminate IR losses due to wire resistance in extended-length cables, this is impossible if you use internal voltage reference of ADS131A04 as an excitation voltage to the bridge. Also, you can use a high voltage excitation source to increase the bridge output as much as possible, so +5V in this design or a higher excitation voltage can be used. 

    Except the voltage excitation, you can also use an internal IDAC to excite your resistive bridge if an ADC with internal IDAC source (for example, ADS124S08) can be used,  see more details in the app note:  A Basic Guide to Bridge Measurements

    Best regards,

    Dale

  • 0 in reply to Dale Li
    Prodigy 90 points

    Thanks for looking into that!