DAC80501: DAC Outputs NOT Responding to SPI Commands

RICK SIMON

Part Number: DAC80501
Other Parts Discussed in Thread: DAC60504, DAC80504, DAC70504,

We encountered this exact same problem after 2 days of chasing it, then finding this link.

https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/994874/faq-dac80501-why-is-the-output-not-updating

While the response was very clear and accurate, for me, the data sheet really needs to be updated to address to state this full response. It is not abundantly clear from just the Recommended Operating Conditions that there is a reference headroom consideration (at lower operating powers) that shuts down the DAC Output Amplifiers.

5 months ago

0 Katlynne Jones 5 months ago

TI__Mastermind 29878 points

Hi Rick,

Just checking, you are no longer having issues with the DAC, is that right? Please do let me know if you are still facing any trouble.

This is described in the reference section of the datasheet and it points to the recommended operating conditions table for the constraints. The section mentions that the outputs will shut down in the reference alarm condition which is what I mentioned in the e2e post as well:

Best,

Katlynne Jones

0 RICK SIMON 5 months ago in reply to Katlynne Jones

Prodigy 150 points

Dear Katlynne,

Thanks for the quick response and yes, we have resolved the issue thanks to finding your post. It appears however, that you have a later datasheet than what we just downloaded from the TI Website. The datasheet we downloaded is

DAC80504, DAC70504, DAC60504

SBAS871C –AUGUST 2017–REVISED JANUARY 2019

and if you look in that same Section 8.3.2, it does not have that extra verbiage.

8.3.2 Internal Reference

The DACx0504 includes a 2.5 V precision bandgap reference enabled by default. Operation from an external

reference is supported by disabling the internal reference in the CONFIG register. The internal reference is

externally available at the REF pin.

A minimum 150 nF capacitor is recommended between the reference output and GND for noise filtering.

The older data sheet does have that type of verbiage in Section 8.3.2.1 in the Reference Divider Section (see below).

8.3.2.1 Reference Divider

The reference voltage to the device, either from the internal reference or an external one can be divided by a

factor of two by tying the REFDIV pin high at power-up or by setting the REF-DIV bit in the GAIN register to 1

during normal operation. The reference voltage divider provides additional flexibility in setting the full-scale output

voltage for each DAC output and must be configured to make certain that there is sufficient headroom from VDD

to the DAC operating reference voltage (VREF/DIV). See the Recommended Operating Conditions table for more

information.

Improper configuration of the reference divider issues a reference alarm condition. In this case, the reference

buffer is shut down, and all the DAC outputs go to 0 V. The DAC data registers are unaffected by the alarm

condition thus enabling the DAC output to return to normal operation once the reference divider is configured

correctly. The reference alarm status can be read from the REF-ALM bit in the STATUS register. Additionally by

setting ALM-EN = 1 and ALM-SEL = 1 in the CONFIG register, the SDO/ALARM pin is configured as a reference

alarm pin.

We must have missed that 8.3.2.1 note! Thanks again for your help!

Rick

0 Katlynne Jones 5 months ago in reply to RICK SIMON

TI__Mastermind 29878 points

Hi Rick,

The screenshot is from the DAC80501 datasheet because that is the part number attached to this post. I didn't realize you were actually asking about the DACx0504 devices. But you are right, the DACx0504 datasheet has this split into the two sections like you mentioned. Same information, just slightly different presentation for some reason.

Please reach out if you run into any more trouble!

Best,

Katlynne Jones

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DAC80501: DAC Outputs NOT Responding to SPI Commands