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ADS1299: HOW MANY ADS1299 CAN BE CONFIGURED IN ONE DAISY-CHAIN

ming liu24
Intellectual 270 points
Part Number: ADS1299

Hello everyone：

  Now I made a 24-ch EEG sampling system using one STM32F4 and three ADS1299EEG daughter board.  The power supply of three ADS1299EEG board is from one ADS1299EEG mother board.

  I met some problem now.I can read the first and second data of ADS1299s, but the data of the last one is 0xff. I wonder how many ADS1299s can be in one daisy-chain system. I see it is said in the manual:"The ADS1299 can be daisy chained with a second ADS1299, an ADS1299-6, or an ADS1299-4." in part 10.1.4.2.

  Could someone tell me how many ADS1299s can be configured in one daisy-chain? Or maybe the power supply is not enough for the three ADS1299EEG daughter board.  Thank you very much.

  • 0
    TI__Guru 62506 points

    Hello Ming,

    The number of ADS1299 devices that can fit in a single daisy-chain depends on the data rate, the SCLK frequency, and the total number of bits to read. Please see equation 10 in the Daisy-Chain Mode section of the datasheet. Remember that each device will have a 24-bit status word plus 24 bits/channel.

    Best Regards,

  • 0 in reply to Ryan Andrews
    Intellectual 270 points

    Thank you Ryan. I check my circuit. The SCLK is about 160kHz and the sample rate is 250sps. So according to the equation is 5.27*1000*1000/(250*(8*24+24))=97.6. Right? So it could be 97 ADS1299s in my daisy-chain. Is that correct? But why I can only read two ADS1299s in the daisy-chain. The daisy-in pin of the last ADS1299 is connected to the DGND, is it right?

    It very kind of you to reply me, thanks again.

  • 0 in reply to ming liu24
    TI__Guru 62506 points
    Hello Ming,

    I'm happy to help. :)

    You're calculation is correct, but I believe you made a typo in the beginning. Your SCLK frequency is 5.277MHz as listed on the right. I'm not quite sure what the 162kHz corresponds to. In theory, you can daisy-chain up to 97 devices, as you calculated above.

    Have you confirmed that the last device in the daisy-chain is working properly? You can probe the power supplies and the /DRDY pin to verify operation. Is it possible to connect only the last ADS1299 device to your MCU and read data from it directly (i.e. disconnect Device 1 and Device 2).

    Best Regards,
  • 0 in reply to Ryan Andrews
    Intellectual 270 points
    Thank you Ryan. Now the question is solved. It is because one wired on board is not connected well. After re-welding the third ADS1299 can be read.
    Thank you for your help. It is very kind of you.