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DDC232: Diagnostic mode seems not working

Stefano Dalpez
Prodigy 70 points
Part Number: DDC232

Dello,

in our application we have two DDC232C connected in daisy chain mode.

The configuration of the register and the readback of the configuration works correctly (data and pattern for both devices).

We are working in the 20-Bit Output mode with a conversion time of 50hz, a data clock rate of less than 2MHz and a master clock of 4.8MHz.

In the data readback, the diagnostic mode seems not working correctly.

In the attached file, you can find the data coming from the convertesrs with input floating and for both cases of diagnostic mode enabled and disabled.

With the diagnostic mode enabled we should have a complete "0" data or the behaviour we have is correct?

Any clue???

Thanks

TI_Forum.pdf

  • 0
    TI__Expert 4680 points

    Hi Stefano,

    Diagnostics mode (bit 0 = 1) just disconnects the inputs from the outside world, so, it is like having zero current. But zero current does not correspond to zero code. It is about 4096 + noise, offset, drifts... 

    Looking at your data, is there a possibility that somehow is shifted by one bit? For instance, the first channel is something like 1000 0000 0111 1001 0100. This kind of pattern repeats across channels, where the first bit is either 0 or 1 then 8 zeros, then 3 ones and then the rest. My theory is that somehow the MSB goes all the way to the back (LSB) either on that channel or on the previous one (all the data stream shifted by one bit). In that way you would have 0000 1111 0010 1001 (3881) which is close to the ideal zero input.

    Please check and let us know...

    Regards,

    Edu