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ADS1232: Settling time stays at 400 ms even when A0 and TEMP is grounded???

Fardin Barekat29
Prodigy 40 points
Part Number: ADS1232
Other Parts Discussed in Thread: ADS1220, ADS122C04

Hi, 

I am having trouble with the ADS1232 chip and nothing makes sense now. 

In my setup I have measuring a load cell with channel 1 input and and have channel 2 grounded. Also A0 and TEMP pins are grounded. My setup is actually very much like the application circuit in the datasheet on page 25 (figure 42). My setup does not have a external crystal either. 

I am using the PDWN pin for energy saving and battery longevity. Every time I need data I am powering up chip with PDWN set to HIGH, and when I get 1 sample I am powering the chip down with PDWN set to LOW. 

The problem I have is speed. The datasheet says there needs to be a settling time of 401 ms after toggling A0, or TEMP. I have both of these grounded and it STILL takes 401 ms for the DRDY pin to go low (sign of new data from page 19). So I ask you all this... What the hell is going on??? 

Please excuse my frustration... 

Thanks in advance. 

  • 0
    TI__Guru** 113765 points

    Hi Fardin,

    Welcome to the E2E forum!  I'm sorry to hear you have frustrations, but I've been there too from time to time when I first start learning a new device.  I think there is a misunderstanding on how the ADS1232 works.  The device has a sinc4 digital filter, and when the device resets the digital requires 4 conversion periods before the digital filter settles.  This happens if you change the mux (A0) pin, the TEMP pin or if you power down the device using the PDWN pin (which resets the device).

    This probably should have been added into the Settling Time section, but when you power down the device, the analog circuitry is turned off and all previous data in the digital filter would be useless anyway.  When PDWN is brought back high, conversions are restarted and the first conversion with settled data will take about 401ms, with the following conversions 100ms thereafter (SPEED pin low).  So the first conversion after PDWN is brought back high will take about 401ms.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 40 points

    Hi Bob, 

    Thank you for your awesome explanation. I just saw the timing graph on the power down section of the datasheet. 

    You are right, the PDWN pin should be included in the settling time section. 

    Thank you for this again. However, my application is time sensitive and I need to conserve power also. Thats why I am turning the chip off after every read and 400 ms is way too long for me. 

    Do you have a recommendation of similar 24 bit differential ADC with a high gain parameter setting?  I was using 128 gain on the ADS1232. 

  • 0 in reply to Fardin Barekat29
    TI__Guru** 113765 points
    Hi Fardin,

    How fast do you need to collect data? What are the resolution requirements for the load cell? What is the capacity and sensitivity of the load cell you are using?

    At the 10sps setting of the ADS1232 you will get the lowest noise. There is also the 80sps setting, will this be fast enough? There are many potential devices, but I would really need to know the answers to my questions before suggesting a good alternative. Price point and device size might also be a consideration.

    Best regards,
    Bob B
  • 0 in reply to Bob Benjamin
    Prodigy 40 points
    I am trying to make a one size fits all solution for load cells. I need the maximum sampling rate to be 100 Hz. I also need high resolution readouts such that the accuracy to be 0.01% full scale.
    Also I need to be able to shutdown the ADC chip and wake it up whenever I need data. From the time I wake the chip up until I get my data should not be long. I need this time as short as possible. (at 100 Hz this time should not be more than 10 ms).

    A nice to have feature of chip is low power consumption.

    I know this is asking a lot but we are in 21st Century... :))
  • 0 in reply to Fardin Barekat29
    TI__Guru** 113765 points
    Hi Fardin,

    Take a look at the ADS1220 (SPI version or ADS122C04 which is the I2C version).

    Best regards,
    Bob B
  • 0 in reply to Bob Benjamin
    Prodigy 40 points
    Thank you Bob. You are amazing!