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ADC12DL3200: input switching problem

Gianpiero Panci
Prodigy 50 points
Part Number: ADC12DL3200

Tool/software:

Hello,

I am working with the ADC12DL3200 in a configuration with Single Input (DES mode) and I need to change which chip input is sampled A or B.

It seems that a simple write in the INPUT_MUX Register (Address = 0x060) is not sufficient to switch the input and the result of this operation is not

stable, sometimes the input is changed sometimes not.  I read all the datasheet but I did not find a specfic procedure required to move the input.

Is there a specific procedure to switch the input? is it required to write other registers to change the input?

thank you in advance

regards

Gianpiero

  • 0
    TI__Mastermind 39050 points

    Hi Gianpiero,

    To fix this, please do a cal trigger after you set the channel mux. This isn't specifically in the datasheet, but this should fix your issue. I also verified this in the lab.

    You can use this sequence below:

    Regards,

    Rob

  • 0 in reply to Rob Reeder
    Prodigy 50 points

    Hi Rob,

    thank you for the support,

    I have tested your solution and it works (in the 0x60 reg we write 0x1 for input A and 0x2 for input B because I work in DES mode)

    only in case of foreground calibration, but the problem is that triggering the foreground calibration causes the reset of calibration data and the restart

    of the calibration process that takes long time whereas my application requires fast switch between inputs.

    In backgound calibration the sequence doesn't work and the input mux do not switch even if I trigger the cal with reg 0x6c as you showed.

    From the datasheet it seems possible to switch the input without restarting the calibration.

    Is there a way  to switch the input keeping the last calibration data and without restarting a new calibration process?

    May I have more details on the possibility to load calibration data thorugh SPI skipping the calibration process?

    Is there any possibility to optimize (write less data than 673 values) the writing of calibration data through the SPI interface? 

    Regards

    Gianpiero

  • 0 in reply to Gianpiero Panci
    TI__Mastermind 39050 points

    Hi Gianpiero,

    I am confirming with the design team, but I do not think you can use the ADC in this way unfortunately.

    Please give me a few more days to respond back.

    Regards,

    Rob

  • 0 in reply to Rob Reeder
    TI__Mastermind 39050 points

    Hi Gianpiero,

    I heard back from design:

    The INPUT_MUX register isn’t really meant to be changed when CAL_EN=1. You are supposed to clear CAL_EN, change INPUT_MUX, then set CAL_EN=1 again. Sorry for the confusion, this is not captured in the datasheet captured appropriately. 

    The INPUT_MUX register is inspected by the calibration engine at particular points in the calibration sequence (and then it configures the input mux, the trims, and some other signals). If background calibration is disabled and foreground calibration has already started (or finished), then changing INPUT_MUX will produce inconsistent behavior.

    Regards,

    Rob