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ADS8904B: AIN input range

Kenta Fujikawa
Prodigy 30 points

Part Number: ADS8904B

I'm looking at the circuit in section 8.2.1 of the datasheet.
In this circuit, ”AIN to GND” is input up to 5V for REFIN = 4.5V.

This exceeds the Absolute Maximum Ratings of Analog Input (AINP, AINM) to GND, VREF + 0.3 = 4.8V, is this a problem?

  • 0
    TI__Guru 51130 points

    Hello,

    Yes, if the output of the amplifier goes to the rail (5V), then this would violate the maximum input voltage rating of the AIN pin.  In this case, there are a few options.

    1. Limit the input range of the amplifier to ensure the amplifier output does not exceed 4.8V.

    2. Use a slightly lower supply voltage for the amplifier, such as 4.8V.

    3. Include clamping diodes on the amplifier output, but this could reduce linearity due to the voltage dependent capacitance of the protection diodes.

    The other option would be to use a 5V reference, and power the ADC and Amplifier from a slightly higher supply voltage, such as 5.2V.  This approach was used on an earlier version of the ADS8900BEVM and worked well.

    Regards,
    Keith Nicholas
    Precision ADC Applications