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ADS124S06: Bipolar Supply configuration REFCOM pin

Renan Santos Adriano
Genius 16570 points
Part Number: ADS124S06

Hello Team,

Good day. My Customer is using ADS124S06, it always measures +-1V differential input and it is the only differential voltage it will measure. They used the Bipolar Analog supply configuration given in the datasheet Figure 119. They also want the internal reference (2.5V) as a bias node for external circuitry.

The question is if REFCOM is connected to AVSS(-2.5V) then they would see 0V on REFOUT but they need 2.5V on REFOUT. So they are thinking to connect REFCOM to AGND or board Ground because they will never measure any -ve input voltages so that they can see +2.5V on REFOUT. Is it ok to do so? If not it means they can never use the internal reference to bias external circuitry when bipolar supply configuration is used?

Can you also explain how internal reference is derived?

Regards,

Renan

  • 0
    TI__Guru** 112935 points

    Hi Renan,

    The REFCOM is to be connected to AVSS with a low impedance connection.  If REFCOM is connected to some other point, the REFOUT may oscillate and not be stable.  The internal reference is derived from the analog supply.  As far as the internal reference is concerned the 2.5V is to be measured relative to AVSS and not AGND.  The REFOUT is +2.5V relative to AVSS.  It may appear to be 0V relative to AGND, but if the negative supply should drift up or down, there would be a measurable difference relative to AGND, but would maintain 2.5V relative to AVSS.

    Even if it were permissible to set the REFCOM to AGND, there would be no advantage using the REFOUT versus the +2.5V supply as there would be no regulation due to lack of headroom.  Why not use the +2.5V analog supply as the bias voltage?  

    Best regards,

    Bob B