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AD5658R Output Voltage Range

Hello,

I am prototyping with the AD5658R DAC and I have it assembled as recommended in the quick start guide with a few exceptions.

The device is powered with 5V. VLogic is tied to 3.3V. GAIN is tied to VLogic(3.3V) and RSTSEL is tied to 3.3V as well.

On testing the device with GAIN of 1(GAIN tied to GND), I have confirmed the range is between 0V and 2.5V.

However, after setting GAIN to 2(GAIN tied to 3.3V), the range seems to go between 2.5V and 5V. I am expecting a unipolar output from 0V to 5V as stated in the datasheet, but the  result is not the case.

Is there something I may be missing? Any help to figure out the problem is appreciated. Thanks!

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  • Hi, 

    Does that mean when you're sending a zero scale command 0x0000 to the DAC input registers, the output is at 2.5Vinstead of 0V? When you trigger a hardware reset using the reset pin at gain=2, the output is at what voltage? it'd be at midscale (2.5V) since your RSTSEL is high, if you set it low and do a reset, the output should be 0V right?

    There might be something we need to check on your serial interface. Are you sure you're following the SPI timing diagram in the datasheet? AD5686R/AD5685R/AD5684R (Rev. E) (analog.com)

    Could you get a scope shot of your SCLK, SDIN, SYNC signals?

  • That's correct, when I send 0x0000 to the DAC input registers, the output is 2.5V.

    When a hardware reset is triggered at GAIN=2, the output is at 2.5V.

    I have just set GAIN to 1(GAIN tied to ground) and can confirm that when i send the 0x0000 it outputs close to 0V and when i send 0xFFFF it outputs 2.5V. However, anything between 1-2.3 V will output a random value between 1.8V to 2.44V.

    In this example I send 0x947B, which is decimal for 38011 and a voltage output of 1.45V based on the transfer function, but the DAC outputs 1.87V. In another case, i send 0xA8F6, the decimal for 43254 and a voltage output of 1.65V, I am getting 2.44V out of the DAC.




    Any help is appreciated, thanks!