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ADS1148: ADS1148

Madhurani Rajaput
Prodigy 40 points
Part Number: ADS1148


Tool/software:

We are using ADS1148IPW in our application. It is sending conversion data to uC through SPI. We are observing a tri-state voltage of 0.5V on this line when chip select is high. What is the ideal voltage level on this line when chip select is high?

  • 0
    TI__Guru 54016 points

    Hi Madhurani Rajaput,

    Can you please be more specific with respect to what you are seeing? Which digital communication traces are you seeing 0.5V when CS is high? Can you provide a schematic of your system?

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 40 points

    Hello, I am probing on DOUT/DRDY line. DOUT/DRDY of ADS1148IPW is connected to MISO pin of uC. When CS(chip select) is high, there is a voltage level of 0.5V on DOUT/DRDY line. We have also connected a 46.4K pull-up resistor on this line. Ideally when Chip select is high the DOUT/DRDY pin should show 3.3V due to pullup resistor but it is having a voltage level close to 05V. 

  • 0 in reply to Madhurani Rajaput
    TI__Guru 54016 points

    Hi Madhurani Rajaput,

    How are measuring the voltage at this pin? Are you using a scope, or a DMM? If you are not measuring with a scope, can you measure with a scope and send screenshots?

    Also, does the voltage change if you remove the pull-up resistor?

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 40 points

    Hello,

    Please find the scope shot:

    1) With 46.4K pullup resistor

    When CS(red) is high, ideal voltage level on DOUT/DRDY (yellow) line should be 3.3V due to pullup resistor. But it is ~0.5V.

    2) Without Pull-up resistor

    I removed pull-up resistor, now the voltage level on Dout/DRDY(Yellow) pin is 0 when CS(Red) is high

  • 0 in reply to Madhurani Rajaput
    TI__Guru 54016 points

    Hi Madhurani Rajaput,

    Thanks for providing this information

    I would remove the pull-up resistor then, it is not really necessary for operation of the device and it seems to be drawing current somehow through the ADC

    An alternative would be to put a larger value resistor as a pull-up and see if the current decreases. Or, if you are okay with the additional current draw on that pin while it is not being used, you can leave as-is

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 40 points

    Hello,

    Thanks for your input. But DOT/DRDY is MISO pin in our configuration. And ideally it should be pulled high right? Activating the MISO pin’s pull-up is done to keep this line in a known state. 

    -Madhu

  • 0 in reply to Madhurani Rajaput
    TI__Guru 54016 points

    Hi Madhurani Rajaput,

    The ADC drives the DOUT/DRDY pin, so it does not need to pulled up unless you want to add this functionality 

    You can see for example in the ADS1248EVM that the DOUT/DRDY line does not have a pull-up on it

    -Bryan