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ADS7946 Reference

Michael K
Intellectual 370 points

Other Parts Discussed in Thread: ADS7946

Hello,

I want to use 16 devices of ADS7946. For the voltage reference I want to use a REF5050. How much is the input current on the REF-pin of hte ADS7946? I did not find this information in the data sheet. REF5050 has an output current of 10mA. Can I use one REF5050 for all 16 ADS7946 converters?

Best regards,

Michael.

  • 0
    TI__Mastermind 23235 points

    Michael -

    Based on the datasheet, the REF5050 is shown in the apps section (page 26) so you should be good with your selection.  Make sure that you have the capacitor as noted to get optimal performance from the ADC.

    In regards to references for multiple ADCs, you should not try and drive multiple ADCs with a single reference device. The performance of this will not be optimal with the ADCs all pulling on the same reference.  If you only want to use one reference, you should buffer the output for each of the ADCs.  So it may be easier to just provide a reference device for each device.

  • 0
    TI__Expert 6925 points

    Hello Michael,

    The issue with one reference for many converters is reference stability and noise.

    Reference pins are dynamic inputs that send kickback currents back to the reference and the reference has to correct the voltage very quickly. The 1uF capacitor helps to attenuate these currents allowing the reference to keep a clean and stable reference voltage for one converter but not for many.

    If the converters are sampled one at time so that all 32 channels are sampled every 2MSPS/32 channels or 62.5KSPS per channel, then it might be possible to share buffers among converters that are located close to each other.

    For example, 2xOPA2350 or 1xOPA4350 can buffer one REF5045. This allows 4 converters per buffer with a 5V supply.

    Could you tell us a little more about your project? For example:

    What will the ADS7946 inputs measure? What is the input range?
    What is the power supply? Since the REF5050 is preferred, it seems the power supply is either 12V or 15V.
    Are low power components required?
    How will the 16 converters (32 Channels) be placed in the board? Are all converters in the same location in the board or are they scattered?

    Thanks,
    Rafael

  • 0 in reply to Rafael Ordonez
    Intellectual 370 points

    Hello Rafael,

    all ADS7946 will be sampled simultaneously in my application. So I understand that it would not be possible to use one REF5050 and an OPAmp for more than one ADC.

    The only possibilities are to use 16 REF5050 (one for each ADC) or to use one REF5050 and 16 separate OPAmps (one OPAmp for each ADC).

    But if I use 16 separate Voltage References for the ADCs, each ADC might have a slightly different reference voltage. So in this case it would be better to use one reference and 16 buffers. I think this is the way I should go. Would you agree?

    Input range and power supply values are not yet decided. Low power components are preferred and all ADCs will be in the same location on the board.

    Best regards,

    Michael.