ADS124S08: Reading data from multiple channels

Part Number: ADS124S08
Other Parts Discussed in Thread: ADS1260, ADS131M08, ADS131M02

Hi TI Support team,

I need a support with reading data from two channels from the adc chip. I understand the auto sequencing feature is not supported by the chip. It's mandatory to write INPMUX register with next channel information before ADC conversion starts.

In addition to above constraint, we have a time constraint for data acquisition. 

Configuration used : 

Currently chip is operating with Low latency filter and SPS of 4000 (every 250us) in continuous operation mode. Data ready signal is used as a trigger mechanism to read ADC data of channel 1. We also need to read channel 2 data.

My requirement is stated below : 

1. Capture both channel 1 and channel 2 data within the span of 250 us. 

Is this possible by any necessary means ?

If not , is there any chip which would support 8000 SPS or above with very minimal or ideally no design changes at Electrical and Software side.

Please let me know your thoughts.

Regards,

Sushrut

  • Hi Sushrut,

    Welcome to the E2E forum!  Unfortunately the fastest data output rate available for the ADS124S08 is 4ksps.  This will actually lower when cycling through the mux as there is some latency involved as the filter name describes.  This is indicated in the ADS124S08 datasheet in Table13.  Note the highlighted value below, which is the best throughput time possible excluding any firmware overhead and communication delays.

    So it will take a minimum of 812us to read two input channels.  A similar Delta-Sigma device that is faster is the ADS1260.  However, the device pinout differs and firmware requirements in the communication would also differ.

    Best regards,

    Bob B

  • Thank you very much Bob for your support. 

  • Hi Bob,


    I went through ADS1260 chip and learnt that this chip does not support the required acquisition rate. 

    Here is my requirement:

    1. Two channels need to be read in 250 us in continuous mode( 4000 SPS ). The DRDY signal is used as an external interrupt by controller. 

    2. Can you please suggests a chip having simultaneous acquisition of two or more channels and provide data at exactly 4000 SPS? 

    Please let me know if more information is needed.

    regards,

    Sushrut Lagwankar

  • Hi Sushrut,

    You initially asked for a similar device to the ADS124S08 and the ADS1260 is similar in operation/features in many ways.  So just knowing the output rate is not clear to what particular features you need from the ADC.  So for device recommendation it is important to understand why the ADS124S08 was initially desired, what features made it desirable and what sensors will be connected.

    Your requirements have changed somewhat.  The ADS1260 can work, but not work quite in the same way as you might think.  If you take the sinc1 filter rate of 40ksps and average 5 measurements per channel you end up with an overall throughput rate of 8ksps per channel or both channels in 250us.

    If you require a simultaneous sampling ADC, you could consider the ADS131M02 (two channel device).  There are other devices in this part family that can have as many as 8 simultaneous sampling inputs (ADS131M08).

    Best regards,

    Bob B

  • Hi Bob,

    We have a specific design that prohibits me from picking up ADS1260. As this DRDY signal from ADC acts as an interrupt which wakes controller from sleep, do it's job and sleep again. This has to happen at 4KHz ( 250 us ). Hence, the acquisition rate of 4000 SPS. But, we are trying to accommodate a new channel into existing design without affecting 4KHz control loop mentioned above. Hence, I wonder if simultaneous ADC sampling would help. I will checkout ADS131M02 chip. Well, I appreciate your help and support. Thanks Bob...

    Regards,

    Sushrut

  • Hi Sushrut,

    That makes sense to me now.  A simultaneous sampling device would make more sense if you are concerned about processor 'awake' time.  If you have questions regarding the ADS131M02, please start a new thread.

    Best regards,

    Bob B