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ADS1278: Behavior for 2 ADC in Daisy-Chain and /PWDN in several channels

Benjamin Nordman
Intellectual 400 points
Part Number: ADS1278

Hello TI Community,

I have a question related to the behaviour I observed on two ADS1278 in Daisy-Chain and communicating with my MCU (STM32H743ZI) in SPI TDM Dynamic (FORMAT[2:0] = 000).

I will call:

ADC1 the ADS1278 whose DIN is connected to GND and DOUT to the pin DIN of the other ADS1278

ADC2 the ADS1278 whose DIN is connected to my MCU

Different cases :

-When all /PWDN of both ADC are disabled (pulled-up) I can observe /DRDY is working.

-When all /PWDN of both ADC are enabled (GND), I can observe /DRDY is not working anymore.

-When all /PWDN of ADC1 are disabled and at least one /PWDN of ADC2 is enabled /DRDY is working.

-When all /PWDN of ADC2 are disabled and even with all /PWDN of ADC1 enabled /DRDY is not working anymore.

It seems that if I disable all the channels of ADC2 the conversion are not working anymore (for comsumption matter when I don't use them).

Could you please explain me why?

I could not find anything about it in the datasheet.

Best Regards,

Benjamin

  • +1
    TI__Mastermind 40610 points

    Hello Benjamin,

    The /DRDY signal is generated by each of the internal ADC's and combined together to generate the output /DRDY signal.  In order for this signal to work, at least 1 of the internal ADC channels must be powered-up and active.  When all channels are disabled in ADC2, the /DRDY signal will no longer work.

    There is no connection, or communication, between ADC1 and ADC2 for the /DRDY signal.  You only need to monitor 1 /DRDY signal for 2 ADCs since both ADCs are synchronized.

    In your case, if you want to be able to use ADC1 with all channels on ADC2 shutdown, then you should monitor both /DRDY pins.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Intellectual 400 points

    Hello Keith,

    Thanks a lot for your reply :-)

    Just a thought: I don't want my MCU getting two different signals. Then, I intend to use a OR-gate to get either of these signals instead.

  • 0 in reply to Benjamin Nordman
    TI__Mastermind 40610 points

    Hello Ben,

    That should work as long as the /DRDY pin is LO with all channels disabled.  I suggest checking this as this is something that is not specified in the datasheet.  Otherwise, it would be best to monitor both /DRDY pins.

    Regards,
    Keith