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ADS1244: Datasheet Inquiry

TI-CSC
Genius 10610 points
Part Number: ADS1244
Other Parts Discussed in Thread: ADS124S08

Hello E2E Experts,

Good day.

  1. I do not understand the "multichannel systems" discussion. How can I use multiple devices on the same channel without a data clash? The section only talked about all DOUTs going LOW but nothing about how to retrieve the data from multiple devices. Please be explicit as possible. Thanks!
  2. The "multichannel systems" discussion mentions the use of multiple devices. Is it ok if I don't use the same channel? I plan to use CLK1, SDO1, and SCLK1 channels for the 1st device and CLK2, SDO2, and SCLK2 channels for the 2nd device. Is this ok?

Additionally, would like to request a design review of the schematic below.

Regards,

CSC

  • +1
    TI__Mastermind 40191 points

    Hi,

    As Figure 18 in the ADS1244 datasheet shows, each ADS1244 has the same SCLK and CLK, but different DOUT lines. So there are no data collisions because you should have separate digital inputs for each ADC going into your controller. You then read data for multiple devices the same as you would for a single device (see the Data Retrieval section on page 11 in the datasheet). The only difference for multiple devices is that you need to identify when each ADC DOUT/DRDY line drops low to indicate new data is ready before you begin the data retrieval process. If you are synchronizing multiple ADCs, the datasheet provides a procedure for ensuring synchronization in the Multichannel Systems section (within time t14).

    The reason the ADS1244 datasheet suggests using the same SCLK and CLK lines for all ADS1244s is to keep the data as synchronous as possible. As stated previously, the datasheet provides a procedure for ensuring synchronization in the Multichannel Systems section (within time t14). If you do not need to synchronize, then it is fine to use separate SCLK and CLK lines for each ADC.

    Regarding the schematic: there is not much here to check, but what is there looks good. One exception: the VREF input is limited to AVDD. You have AVDD = 3.3V and VREF = 5V, which is a violation of the datasheet requirements. Also, footnote 6 on page 3 in the ADS1244 datasheet states that it is not possible to reach the digital output full-scale code when VREF > AVDD/2. Please keep this in mind.

    Finally, I would point out that we have released newer generations of the ADS124x devices, such as the ADS124S08. If you need to read multiple inputs using a multiplexed ADC, the ADS124S08 is the next-next generation of the ADS1244. Please keep this new ADC in mind for future designs. Or, if you have more questions about the ADS124S08, please let me know.

    -Bryan