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ADS1278 data problem

Gilbert Morton32
Prodigy 10 points
Other Parts Discussed in Thread: ADS1278, ADS1278EVM-PDK

We are using an ADS1278 and are having some issues with the converted data.

The 1st 3 channels are shorted together. The 1st channel data looks correct. The 2nd and 3rd channel data looks like the sign could be flipped.

We are reading the 8 channels via the pseudo SPI from a SM470R. We read 24 bytes all between the /DRDY pulses.

I will try to get some scope captures.

The problem seems to be very similar to this problem, but it is not clear to me what we can change / tweak:

https://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/43479

Please advise.

· End-application - High temp electronics
· Detailed problem description - See above
· What is your input signal - 4.3 Volts
· Supply voltages - AVdd=5V, IOVDD=3.3V, DVDD=1.8V 
· Reference voltage- Vref=2.5V
· Input and reference drive circuits - Reference is driven from a REF5025SHKJ, Inputs come from an OPA211SHKJ low pass filter.
· Digital control pin settings (i.e. Reset, PowerDown, Start, etc.) - Format0=1. Format1=0, Format2=0, Clkdiv=1, Mode0=1, Mode1=1, /Sync=1, /PwrDwn=1

  • 0
    TI__Guru 66706 points

    Hi Gilbert,

    Yes, please provide those scope captures if you can, preferably with DOUT, SCLK, and /DRDY together. Have you designed your own PCB for the ADS1278, or the ADS1278EVM-PDK?

    Also, what is the CLK and SCLK frequency you are using? I could check your timing specs for you.

    You mentioned that your input signal was 4.3V. Just for clarification, you mean that your channels inputs are shorted together and tied to a 4.3V common-mode, such that the differential input voltage is ~0V, correct? It might be worth repeating the test you found in the related post and use a small negative differential input voltage (i.e. -100mV) such that the leading 8 or so MSBs are 1's and the issue becomes more apparent.

    Best Regards,