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AD5672R not setting its output to default value while in RESET

Hi,

I am not able to use the RESET pin to set the DAC outputs to default values before I program the DAC.

Here is what I do :

- RSTSEL is set to VLOGIC, because I want a default output voltage of 2.5V

- t0 : DAC V_LOGIC is supplied with 3.3V ; RESET is hold high

- t1 : DAC VDD is supplied with 5V

- t2 : RESET is set low for 10ms, and back high. I did this to be sure the DAC outputs were at a safe value (2.5V) before I program the DAC. But it does not work: the DAC outputs stay at 0V during the 10ms RESET.

- t3 : I program the DAC to output a voltage of 3.3V. It works properly

Am I doing something wrong? Why don't I have 2.5V at the output of my DAC during RESET? 

One funny thing iI noticed is that if I keep the RESET pin high all the time, the DAC is setting its output to 2.5V after is it powered up, which is what I want. But it is doing the opposite of what is said in the datasheet... I need this to be clarified.

Thank you,

Maxime Puech

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  • Hi Maxime,

    The output will only go to the determined reset value as dictated by the RSTSEL value 'after' RESET pin is released or pulled back to logic high.

    As long as RESET pin is low, the output is 0V.

    This is the expected behavior of the part, is this what you're observing?

    Cheers,

    Ivan

  • Hi Ivan,

    Thank you for your answer. Yes this is the behavior I am onserving; the part behaves as expected. But I think the datasheet is not clear enough about this.

    It leads me to another question. What happens on the DAC outputs if I never reset the DAC by keeping the RESET pin high all the time? Does the DAC have a power on reset ? Will the DAC go to the determined reset value as dictated by the RSTSEL pin by itlsef?

    Thanks,

    Maxime

  • Hi Maxime,

    Sorry I did not understand your question. But the part will still reset of you cycle the power or supply of the DAC due to the POR block. And yes, the output state after reset will be dictated by RSTSEL pin.

    One more way to reset is to use the SOFTWARE RESET command.

    Cheers,

    Ivan

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