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ADS131A04: Can I use unipolar supply with negative charge pump enabled, and bipolar input?

Howard Zou
Genius 12365 points
Part Number: ADS131A04

Hi, when negative charge pump enabled, we can accept as low as AVSS-1.5V input at VINP and VINN.

So when I apply AVDD=3V, VREF=3V, VINN=1.5V, VINP ranges from -1.5V to 1.5V, the ADC can still work well, right?

The only bad effect is that the input is equal to -3 to 0V range, so the corresponding digital output will not be full scale, only 0-2^23, right?

  • 0
    TI__Guru 57346 points

    Hello Howard,

    Thank you for your post.

    The negative charge pump allows the absolute input voltage to range from AVDD to (AVSS - 1.5 V). For VINN = 1.5 V, the differential input voltage will never be positive if VINP = -1.5 V to 1.5 V.

    If you are looking to utilize more of the ADC full-scale range, you should connect VINN to GND. The differential input voltage would then be equal to VINP (+/- 1.5 V).

    One detail that needs attention in the configuration you described is the reference voltage. VREF = VREFP - VREFN must remain 500 mV less than AVDD. For AVDD = 3 V, the maximum reference voltage you can use is 2.5 V.


    Best Regards,

  • 0 in reply to Ryan Andrews
    TI__Genius 12365 points

    Ryan,

    thank you.

    But according to datasheet, Vcm should be within AVSS and AVDD, so when Vinp ranges from -1.5 to +1.5, I can only set Vinn=1.5 and keep the differential input voltage to be -3 to 0.

    In this state, I can still use this device with some constraints(no positive differential input). 

    If I keep Vinn=0, I can't use this device, right?

  • 0 in reply to Howard Zou
    TI__Guru 57346 points
    Hi Howard,

    I believe the common-mode range in table 7.3 assume the negative charge pump is disabled. Notice this is in the Recommended Operating Conditions table, it is not an Electrical Characteristics specification.

    I will confirm with a designer whether the input common-mode range changes when the negative charge pump is enabled.

    Best Regards,
  • 0 in reply to Ryan Andrews
    TI__Genius 12365 points
    Thank you.
    Waiting for your confirmation.
  • 0 in reply to Howard Zou
    TI__Guru 57346 points

    Hello Howard,

    The input common-mode range should match the analog input range. When the negative charge pump is enabled, the input common-mode voltage can range from AVSS - 1.5 V to AVDD.

    Best Regards,

  • 0 in reply to Ryan Andrews
    TI__Genius 12365 points

    Thank you.

    So I'll tell the customer that they can use the device as you mentioned.