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CCS/DAC8568: Can not get DAC8568 working...

Dennis Warncke
Prodigy 130 points
Part Number: DAC8568
Other Parts Discussed in Thread: MSP432E401Y, REF5030

Tool/software: Code Composer Studio

Hi all!

I have a Prototype PCB with an MSP432E401Y and a DAC8568.

My setup is, as stated in the data sheet:

LDAC pin is tied low,

CLR pin is tied to 3V3.

For the ref Voltage I implemented a REF5030, which is currently not connected (solder jumper), as the internal Reference is still present (2.5V).

I did a record with a logic analyser on my launchpad, as in the final design its pretty difficult to access the pins.

As you can see the following commands are transfered:

0x08 00 00 01

Enable int Reference

0x04 00 00 FF

Power up all DACs

0x05 00 00 03

Ignore CLR pin

0x06 00 00 FF

Ignore LDAC pin

0x03 FF FF F0

full Output on all DACs

The output stays 0, in the default state. When I try to disable the internal Ref, its still there...

Any help is appreciated.

  • 0
    TI__Mastermind 18546 points

    Hi,

    Thanks for writing to us.

    Since your first command is acknowledged by the device by enabling the internal reference, I feel there no issue with your SPI communication.

    Whats the SCLK frequency here? and whats the SYNC high time for subsequent frames?

    Can you please share a rough sketch of your DAC connections?  Also are you looking for synchronous update with software control? 

    As a debug, can you do the following

    1. Power cycle DAC

    2. Measure Internal Reference ( it should be zero after power up)'

    3. Enable Internal Reference (write 0x08 00 00 01).

    4. Measure Internal Reference  ( it should be 2.5V)

    5. Enable output of DAC (write 0x04 00 00 FF)

    6. Send DATA to any of the DAC channel ( for eg  write 0x03 FF FF F0)

    7. Measure output on the corresponding DAC channels)

    Please note that I didn't write CLR and LDAC modes ( for synchronous update, its not required, unless you want software mode LDAC)

    Regards,

    AK

  • 0 in reply to Akhilesh K
    Prodigy 130 points

    Thank you for your ideas so far!

    Akhilesh K said:
    Since your first command is acknowledged by the device by enabling the internal reference, I feel there no issue with your SPI communication.

    Well, even when I deactivate int Ref, its activated - maybe the IC is damaged, because it should be deactivated by default right?

    Akhilesh K said:
    Whats the SCLK frequency here? and whats the SYNC high time for subsequent frames?

    SCLK is 2 MHz and the SYNC High Time is around 1.2µs (LA ran at 10MHz)

    Akhilesh K said:
    Can you please share a rough sketch of your DAC connections?  Also are you looking for synchronous update with software control? 

    Akhilesh K said:
    As a debug, can you do the following

    I did that, but unfortunately the int Vref ist always present, even at start up with no comman being sent. The output remains 0 for all channels.

    ___________

    Update:

    I didn't unplug the JTAG cable... when I completly unplug the PCB it starts with 0V on int Ref, but the other commands don't seem to work...

  • 0 in reply to Dennis Warncke
    TI__Mastermind 18546 points

    Hi,

    On power up, internal reference is powered down, I am now confused how you can get 2.5V at power up.

    Did you try doing the steps I mentioned above after power cycling the device? 

    Can I get a scope shot of your SPI transaction?  Also Can you do Software RESET as a debug?

    I will check this behavior with my internal team and get back to you ASAP.

    Regards,

    AK

  • 0 in reply to Akhilesh K
    Prodigy 130 points

    Ok I found the issue, after just powering up the DACs, the internal Ref was coming up (so 0x04 vs 0x08)...

    I ended up changing SPI phase, and voila it works.

    Anyway thank you very much!

  • 0 in reply to Dennis Warncke
    TI__Mastermind 18546 points

    Hi,

    I am glad that your problem got solved. 

    Regards,

    AK