DAC7578: DAC7578 zero-code error

Howdy Karim,

Can you publish your schematics surrounding the device? If you don't want these to become public I can forward you my contact information and we can discuss offline? Additionally, can you verify all voltages provided to the DAC7578 device?

Best Regards,
Matt

Hi Matt,

Sure, I can share it here, that shouldn't be a problem.

Voltage supply used is 5v or 3.3v (I tested with both).

Thanks for the help.

Cheers,

Karim

Howdy Karim,

A few more questions:

• Have your verified the DAC output at other voltages? -- such as midscale, full-scale.
• Are the analog outputs floating in the schematic above, or are they tied to a load? If so, what type of external load?

Your schematic looks correct, and I don't see anything that jumps out at me, but I plan to recreate your setup in our lab.  I'll update this post with my findings, which should be in a day or two.

Best Regards,

Matt

Hi Matt,

- Yes, I verified the DAC operation almost at all output levels, seems fine without any offset, nonlinearity or gain errors, only the zero-code problem.
- The output is connected to a multimeter, so technically an open circuit, I can try it with a load and update you if there is anything different.

Thanks,
Karim

Hi Matt,

I have attached a basic test log just to give a little help, output voltage versus different codes (0-, 1/4-, mid-, 3/4- and full-scale).

Thanks,

Karim

test_log_3.3v_no load.xls

Thanks Karim,

I'm hoping to have results by tomorrow, so keep a look out.

Best Regards,
Matt

Hi Matt,

Any updates on the test results?, were you able to reproduce the issue in the lab?.

Thanks,

Karim

Howdy Karim,

So far I've been testing with the DAC7678, which is a sister device that shares the same EVM as the DAC7578, and I'm not able to verify any irregularities at zero-scale, or other code values. Looking at the xls, it shows significant error at different code values, which I would think is due to the reference or I2C code.

Out of curiosity, does the 0.4V value show after you power-cycle, or does it only appear after you write to the DAC with code 0? If this (power-on) value is different from what you programmed, then I think it is a software issue. Upon power-up the DAC registers are filled with all zeros to output zero-scale. Can you verify the DAC voltage after power-up with no register writes?

Since I don't have a DAC7578EVM on-hand, I will need to order one. Once I receive the EVM and test I will upload the test results to this post.

Best Regards,
Matt

Hi Matt,

Thanks for getting back to me.

Unfortunately the 0.4v appears at power-up and when writing a zero code via I2C, plus the output seems semi-linear with a gain error that's decreasing when we go higher in code.

As for the DAC7578EVM, please let me know if you get to any similar findings, I appreciate your efforts and time to help.

Thanks,
Karim