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ADS131A04EVM: Signal range for input overrange and underrange detection

Indi
Prodigy 20 points
Part Number: ADS131A04EVM
Other Parts Discussed in Thread: ADS131A04

Hello, This is a question about the analog input signal range which will not trigger an out-of-range error in the status register. According to the datasheet (www.ti.com/.../ads131a02), the permitted analog input voltage range is from AVSS - 1.65 to AVDD + 0.3 Volts (with charge pump enabled). This would indicate that tying either input (AINxN or AINxP) to the ground would not trigger an out-of-range error, but when we try this on the evaluation board, the F_ADCIN error bit and the corresponding bits in STAT_P and STAT_N indicate an overrange/underrange error.

I am unable to find any clear definition of the voltage that triggers this error. The description of COMP_TH (fault detect comparator threshold) seems to indicate that no error should be triggered when the inputs are within 5% to 95% of the input range (when configured to the maximum range). Is there some application note which gives more detailed information about this?

Thanks

  • 0
    TI__Guru* 92715 points

    Indi,

    I'm sorry I haven't answered your question, but I've been out of the office. 

    There isn't an application note for this overrange/underrange detection function on the ADS131A04. Have you tried to set the inputs to a mid supply level (above ground) to make sure that the negative charge pump is operating? Normally, once the inputs are within range, the flag should clear, and is checked and latched for each conversion.

    I'm still out of the office, so I won't have a chance to check this with an EVM until next week.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 20 points
    Hi Joseph, thanks so much for the reply.

    We figured it out, thanks to your hint about the charge pump. I had overlooked the jumper JP8 on the EVM (www.ti.com/.../sbau259a.pdf) that shorted the charge pump to VSS. Once this was removed, the error bits cleared as expected (even for inputs below zero)

    Indi