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Original question:

DAC8771: Iout Load open issue

DAC8771: Open Output when current mode

Hideki Hayashi1
Expert 7350 points
Part Number: DAC8771
Other Parts Discussed in Thread: DAC8775

Hi DAC team,

Customer have question about a behavior when output is open. This is related to below link.

https://e2e.ti.com/support/data-converters/f/data-converters-forum/792835/dac8771-iout-load-open-issue

Your team mentioned "when the load is open in current output mode the voltage will increase in an attempt to drive the current to around 22V in full tracking mode."

If the alarm actio register is set to '01', I don't understand why the output voltage stop to increase around 22V. If no action is taken internally, I think output voltage increase as high as possible and it'll be broken. Also the value of 22V isn't shown on anywhere of the datasheet, is it correct value?

Would you let me know a behavior happen when output load goes to open?

In addition, is the DAC8771 going to be damaged if no action is taken after the output voltage keeps 22V?

Best regards,

Hideki 

  • +1
    TI__Guru* 93975 points

    Hideki-san,


    When an IOUT is set and the output is open circuit the buck-boost converter does not continue to go up and up. The VPOS is limited based on the configuration of the device. I'm not sure why this table was not inserted into the DAC8771, but Table 1 of the DAC8775 (the four channel version) shows the behavior of the buck-boost when IOUT is open circuit. I've clipped it out of the DAC8775 datasheet:

    When the output is open loop, the VPOS goes to about 20V. In the other post, they had said 22V and I've seen it at 21V when I just tested it. Also, I've tested it when the negative buck-boost is disabled, and the VPOS does go to about 32V. When the output is open loop, VPOS should should settle to either the 20V or 32V levels. Not having a load should not damage the device.


    Joseph Wu