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URGENT: Problem with ADC (TLC3544)

matijejer
Prodigy 10 points
Other Parts Discussed in Thread: ADS7280, TLC3544

I've been trying to configure the ADC (TCL3544), connected to a dsPIC33 via SPI. The uC is sending the signal properly but the ADC is not respondig. Already tried with the Hardware Default Mode and Software Programmed Mode but haven't been able to get a correct reply from the device.

I've recently worked with de ADS7280 and had no trouble at all.

I send you a screen capture of the SPI signals taken with a logic analyzer and haven't found the reason for the misbehavior.  They show several configuration commands sended but the result (SDO) is not coherent . 

In the figure the device is configured as follows:

AA02h =>  External V reference, USB, ShortSampling, Internal OSC, Single-ended input mode,  INT/EOC used as INT.

It took 52 External CLK pulses for INT/EOC to occur:

  

 If there is no External Clock pulses INT/EOC doesn't change it state:

 

 The AD input  has a 2.50V level and the result obtained is 3078H (in USB format = 3,78V , in 2's complement=1,28V).

  • 0
    TI__Guru**** 174226 points

    Hi Jejer,

    Welcome to our forum! 

    Change the Polarity and Phase setting of your controller to the TLC3544.  In micro-controller mode (where FS = 1) the ADC is expecting to see a inactive low dwelling clock with (POLARITY = 0) valid data on the falling SCLK edge.  If you look closely at your logic analyser plots, you should notice that SDI and SDO are out of phase, SDO is valid on the falling SCLK while you have SDI valid on the rising, changing on the falling.

    Let us know if that clears up your problems.

  • 0 in reply to Tom Hendrick
    TI__Guru**** 174226 points

    Hi Jesper,

    Did changing the clock polarity/phase resolve your problem?