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ADS8634SRGER - Inconsistency in output

Nanjunda M
Expert 2485 points
Other Parts Discussed in Thread: ADS8634

Hi,

We are using ADS8634SRGER, this ADC in my design to convert the analog signals into digital value.

We have given the +15V and -15V power supply to the IC.

We also have a DAC DAC7716SRHAR in our board, which is also connected to same +15V and -15V power supplies.

We are giving a digital input with the help of SPI interface to DAC, and the Analog output from the DAC is given as input to the ADC IC with an intermediate OPAmp for analog channels. Digital ends of both the ICs are connected to a processor.

But We observing inconsistency in the output of ADC. for example, for the 1st time, if you send a 5 as input to the DAC and you get 5 as output. But when you try for the 2nd time with different value, it gives the unreliable values or the previous value.

Can you please help me out in solving this issue ASAP.

Thanks & Regards,

Nanjunda M

  • 0
    TI__Genius 9975 points

    Hello Nanjunda M,

    From your description it would seem to me that you need the ADC driver circuitry to settle within the time between two consecutive serial interface transactions.

    Could you please include a schematic of your system and tell us what data rate you are using?

    In your post you wrote: “But when you try for the 2nd time with different value, it gives the unreliable values or the previous value”. Could you please include two or three sets of data exemplifying these cases? For each of these examples: could you please capture about 100 codes sent to the DAC and the corresponding 100 acquisitions from the ADS8634?

    Thank you and best regards,

    Jose