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ads8688 ADC converter 8 isolated channel or not?

T L
Prodigy 20 points
Other Parts Discussed in Thread: ADS8688

Hello, TI supporting team.

we want to use ads8688 ADC converter.

Are those 8 channel isolated or not?

Or are those 8 gnds connected inside the chip?

Or we want to use one analog signal from high power side (which is between +/-10V, 100k hz, all the other are low power and control side), does the signal need to be isolated before entering ads8688?

Thanks

  • 0
    TI__Mastermind 44680 points

    Hi T L

    I'm moving this post to the Precision ADC forum where the proper device experts will respond.

    Best regards,

    Jim B

  • 0 in reply to Jim Brinkhurst1
    TI__Genius 9165 points
    Hello T L,

    Welcome to TI E2E forum & thanks for choosing TI.

    ADS8688 input channel are not isolated from each other. The 8 GND pins are expected to be connected to the ADC GND externally.

    If the GND in is not connected directly to the ADC GND, maximum allowed variation on these pins is +/-100mV wrt ADC GND to guarantee specified performance.

    If you want isolation between different inputs, then you will need an analog isolation between your input and each ADC analog input.
    Also, the ADC front end consists of PGA & 2nd order low pass filter. The 3dB cut off frequency for the LPF is 15kHz. Hence your 100kHz signal will get heavily attenuated by front end. For other control signals we should not have any issues as far as signal frequency does not go beyond 15kHz.

    If you can share more information regarding your project, we can suggest suitable option.

    Thanks & Regards,
    Shridhar.
  • 0 in reply to Shridhar%20More
    Prodigy 20 points

    Thank you Shridhar,

    It is great you are with us.

    Is DVDD/DGND(Digital supply) electrically isolated from AVDD/AGND(Analog supply) inside of the ADC chip?

    We are considering use one set of digital power supply supply (same as for microprocessor through SPI) to power DVDD/DGND, and use another set of independent analog power supply to power this ADC's AVDD/AGND, if these DVDD/DGND(Digital supply) electrically isolated from AVDD/AGND(Analog supply).

    If not, we will have to use a digital isolator such as AduM3151 to isolate the SPI/with 2 more I/Os.

    Our system sampling frequency is 100Khz, but control loop BW is about 4Khz, so we assume 15Khz cut off frequency on LPF is ok for the current sensing .

    TL

  • 0 in reply to T L
    TI__Genius 9165 points
    Hello T L,

    The DGND & AGND are not electrically isolated inside the ADC.

    You will need to use external digital isolator such as ISO7141.

    Thanks & Regards,
    Shridhar.