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initialization problems with the DAC7562

Stefan Merk
Prodigy 30 points
Other Parts Discussed in Thread: DAC7562

Hi.

I have some problems with the DAC7562.

The SPI communication is OK. I can see the frames on the oscilloscope. But I get no output signal and no internal reference on the depending pin.

In which order must the config frames send? I couldn't find any documentation for this.

 

Thanks a lot.

  • 0
    TI__Mastermind 43915 points

    Hi Stefan,

    By default, the DAC7562 powers up expecting an external reference for conversions. You will need to write to the device to enable the internal reference. Depending on if you want a range of 0-2.5V or 0-5V will determine which code to write to the device to both enable the internal Vref and set the internal gain (used to determine whether you have 2.5V range or 5V range).

    My first recommendation is to apply an external voltage to the Vref pin to verify that you have communication working properly and you are able to successfully write and update the DAC. After that, you can remove that voltage and write to enable the internal reference. If you would like to enable the internal reference in a gain of 2 (0-5V range), you will want to write 0x380001. You can then probe the Vref pin to verify it is powered correctly.

    Regards,

    Tony Calabria

  • 0 in reply to Tony Calabria
    Prodigy 30 points

    Hi Tony,

     

    thanks for your answer.

    I tested the things you told me to do. If I connect an external reference (~ 2.5V) to the dependend pin and (gain A=1;B=1) write a "Write to DAC-A input register"-command to the SPI (data is 0xFFF), I got an output voltage of ~5.17V. If th gain is set 2 for both channels, I got an output of ~2.59V.

    This result is a little bit confusing, but the main problem is now, that I could not activate the internal reference.

    Here are the SPI-commands which I send to the DAC in my init function.

     

    MSB...LSB

    30 00 30     // disable LDAC-Pin for both

    38 00 10     // enable internal ref

    02 00 30     // gain: A=1 ; B=1

    20 00 10     // power up DAC-A

    20 00 20     // power up DAC-B

     

    Thanks a lot!

     

    P.S.: Sorry for the bad english.

  • 0 in reply to Stefan Merk
    TI__Mastermind 43915 points

    Hi Stefan,

    Looks like what you are setting are not the correct commands. The commands you currently are writing are 20 bits (with the last four bits as zeroes) but should be 24 bits. Below is what the commands you are writing should look like.

    30 00 30               // disable LDAC-Pin for both --------> 30 00 03
    38 00 10               // enable internal ref ------------------> 38 00 01
    02 00 30               // gain: A=1 ; B=1 ----------------------> 02 00 03
    20 00 10               // power up DAC-A --------------------> 20 00 01
    20 00 20               // power up DAC-B --------------------> 20 00 02

    Let me know if I can help more.

    Regards,

    Tony Calabria

  • 0 in reply to Tony Calabria
    Prodigy 30 points

    Hello Tony,

     

    you're right. I sent the wrong commands. Thank you very much for your support.

     

    I wondering that the datasheet have about 50 pages, but there was no sentence, that the last four bits of the 3 Bytes SPI command are only "don't care" if the command should write one of the input registers.

    I think a short initialization example would be really helpful.