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ADS7853: Communication signal status when CS signal disable

Liu Bin
Prodigy 20 points

Part Number: ADS7853

Hello,

I plan to multiplexed the SCLK, SDI and SDO_A signal with another SPI interface signals, I want to know whether the SCLK, SDI and SDO_A signals can be configured to HiZ when CS signal of the ASD7853 is disabled.

Thank you for your response.

Bin Liu

  • 0
    TI__Expert 7960 points

    Hello Liu, 

    Thank you for your question! 

    The SCLK signal is an input so that should not be an issue, and can also be shared with other devices that need the SCLK.

    The SDO_A and SDO_B do get configured into a high impedance tri-state when the CS is high. 

    Typically with multiple SPI devices, if synchronized, SCLK and CS can be shared with only individual SDOs per device. Or in the case where you can multiplex the SDO the SCLK could still be shared with either separate CS lines or muxed CS lines

    What kind of approach are you planning for your system? 

    Best regards, 

    Yolanda 

  • 0 in reply to Yolanda Gonzalez
    Prodigy 20 points

    Hello Yolanda,

    My planning is that SDO_A and SCLK are shared with separate CS lines, SDO_B not used.

    please provide your opinion, thank you.

    Bin Liu

  • 0 in reply to Liu Bin
    TI__Expert 7960 points

    Hello Liu, 

    If SCLK and SDO lines will be shared I will suggest considering:

    • Adding a small resistor in series in each SDO line (~33Ω-100Ω) and/or using a multiplexer 
    • Add a pull up resistor on CS lines to ensure that they are pulled high in when idle, at power up/down, reset, and other possible undefined times. 
      • This will help avoid incidental driving of multiple SDO lines at a time during unknown states where supplies or controllers are not fully configured. 
        • If using a multiplexer, care can be taken to ensure all SDOs are or can be disconnected at power up/down, during different events. 
    • CS asserting/de-asserting timing considerations. Make sure to have guard times between setting one CS high and setting the next CS low to avoid driving multiple SDOs (especially if multiplexer is not being used)
    • If not all devices sharing SCLK and SDOs are not ADS7853 then ensure same SPI protocol can be used with all devices on bus. 

    Best regards, 

    Yolanda

  • 0 in reply to Yolanda Gonzalez
    Prodigy 20 points

    Hello Yolanda,

    Got it, thank you.

    Bin Liu