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CCS/ADS8332: if the INX inputs have a voltage which is working in Vref to Va , the linearity or performance of converter would not meet specifications?

Part Number: ADS8332
Other Parts Discussed in Thread: ABS

Tool/software: Code Composer Studio

ADS8332 has 8 channels analog input voltages. In practice, some channels work in voltages of Vref to VA, some channels work at voltages of 0 to Vref. Then the operating voltage is VREF to VA range of channels, the ADC conversion value is 0XFFFF, the operating voltage is VREF to VA range of channels, and the ADC conversion value is Vadc/Vref*65536.

Question: Does ADS8332 meet this condition?

  • Hello,

    Welcome to the TI e2e community.

    When the input voltage of the ADS8332 exceeds the reference voltage (Vref), the output conversion result will be 0xFFFF.

    Vin=0V, output code 0x0000
    Vin=Midscale=Vref/2, output code 0x8000
    Vin=Full-scale=Vref-1LSB, output code 0xFFFF
    Vin>Full-scale (Vref to VA), output code 0xFFFF
    Vin>VA+0.3V, device may be damaged.

    Regards,
    Keith N.
    Precision ADC Applications
  • Hello,

    Thanks for your reply.

    In ADS8332 datasheet,“Care must be taken regarding the absolute analog input voltage. To maintain linearity of the converter, the INX inputs, the COM input, and the input span of (INX – COM) should be within the limits specified. If these inputs are outside of these ranges, the linearity of the converter may not meet specifications. ”.

    I just care about those channels whose operating voltage is VREF to VA range wheter or not affect the adc result of those channels whose operating voltage is below VREF.

    And when the voltage transits from above VREF to below VREF, the ADC result will still meet specifications.
    In general , wheter this working condition is normal operation of the ADS8332.
    Best Regards,
    Zheng Shuimei.

  • Hello Zheng,

    Channels with input voltage greater than VREF (and less than VA+0.2V) will not effect the accuracy of the channels with input voltage less than VREF. Channels with input voltages greater than VREF will have output code of 0xFFFF, and channels with input voltages from 0V to VREF will have output code of Vadc/Vref*65536.

    When the channel with input voltage greater than VREF is reduced to less than VREF, then the channel will also have an output code of Vadc/Vref*65536.

    Example (VA=5V, Vref=4.096V):

    Conversion N
    IN0 = 5V, IN0 output code 0xFFFF
    IN1 = 2.048V, output code 0x8000

    Conversion N+1
    IN0 = 2.048V, IN0 output code 0x8000
    IN1 = 2.048V, output code 0x8000

    Please note, if the voltage on IN0 exceeded VA+0.2V (assuming the current is limited to prevent damage), then this condition could effect the reading on IN1. If IN0 exceeded VA+0.3V (ABS MAX), then device could be damaged and may no longer meet specifications.

    Regards,
    Keith
  • Hello Keith,

    Thank you very much for your careful answer.

    I will continue to do the actual verification of the ADS8332. If there is any problem, I will give feedback in time, thank you.

    Zheng shuimei