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ADS1158: Pull up/down resistors

jars121
Intellectual 635 points
Part Number: ADS1158

Is it necessary to use pull up/down resistors on the conversion control pins when interfacing ADS1158s with push-pull type MCU inputs/outputs? I'm not using either of the PWDWN or RESET functions, so those particular pins are pulled up to DVDD with 10k resistors. I'm using a 10k pull up (external) on the chip select lines, but am not sure about the START and DRDY lines. START is active HIGH, so would a 10k pull down (external) be beneficial? Similarly, DRDY is active LOW, would a 10k pull up (external) be beneficial?

Would there be any reason to use pull up/down resistors on any of the SPI lines (I don't believe so)?

  • 0
    TI__Mastermind 44680 points

    Hi jars121,

    The pulling resistors are not necessary if your MCU is able to drive them during normal operation; however, there are two benefits I see that might make you decide to use pulling resistors on a few of the ADC control signals:

    1. If you don't plan to use a particular signal and/or you are low on MCU pins, then some of the signals can be fixed with a pulling resistor and you don't have to program your MCU to do anything with those pins.

      1. However, if you don't have a shortage of MCU pins, you might use the MCU in-place of the pulling resistor(s) and potentially update your software in the future to use those pins, if you so choose.

    2. During power-up or MCU initialization routines, the ADC control pins are likely to be left floating if no pulling resistor are present. Adding pulling resistors can help to provide a predictable and smoother power up. That being said, you can usually just account for this unknown behavior in your software initialization routine by first setting /PDWN high, and then toggling the /RESET pin (or toggling /CS to restart the SPI communication and issuing a RESET command) to recover control of these signals and make sure that the device defaults into a known state.

    Regarding which pins require pulling resistors...I would prioritize /PWDN and /RESET first, and then perhaps /CS and START next. /DRDY is driven by the ADC and does not require any pulling resistor, since you have full control in software to ignore the state of this pin until you need it. The SPI signals are driven while /CS is low, otherwise they are ignored so I don't see any need for pulling resistors there. I hope that helps!

     

    Best regards,
    Chris

  • 0 in reply to Christopher Hall
    Intellectual 635 points
    Thanks as always Chris, really appreciate your input!