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ADS8686S: Termination of pins when using the ADC in software mode

Dhir Gandhi
Prodigy 180 points
Part Number: ADS8686S

Tool/software:

Hello,
I plan to use the device in 1-wire software serial mode. I don't want to leave the SDOB pin floating. Could you please advise on its termination? Also, please suggest whether I should use pull-up/pull-down resistors for the following pins:

1. SDI
2. SDOA
3. SCLK
4. CS
5. BUSY
6. CONVST

  • 0
    TI__Guru**** 180901 points

    Hi Dhir,

    Sorry for the delay in getting back to you.  SDOB is an output pin, you do not need to terminate it.  There is no issue leaving it float, but if you feel you need to do something, use a 10K to ground.  There is no need for pull up or down on the remaining pins.

  • 0 in reply to Tom Hendrick
    Prodigy 180 points

    Hi Tom,

    Thanks for the clarification. My main goal is to avoid any unpredictable behaviour, such as situations where the MCU is still powering up while the SPI device is already active. I was thinking that adding a pull-up or pull-down resistor might help in this case. Pls share your thoughts on the same.

  • +1 in reply to Dhir Gandhi
    TI__Guru**** 180901 points

    Hi Dhir,

    Table 6.1 in the ADS8686S datasheet shows the ABS MAX ratings of the device.  The digital I/O are what connect to your MCU and they are controlled by DVDD which is ideally the same power source as your MCU.  Your MCU is controlling the SPI interface, so there really should not be any issues.  You could use a pull-up on /CS and /RESET if you think noise might accidently trigger those inputs.  Smal series resistor (33-100 ohms) in series with SCLK, SDI and SDO can help reduce emissions.