How to turn off output of AD5761?

Hi, 

To turn off the output, you send a command to set the output to zeroscale. The code would depend on what output range setting and B2C bit you're using.

Another way is to issue a /RESET pulse which returns the AD5761 to itsdefault power-on status where the output is clamped to ground and the output buffer is powered down.

If you're using the unipolar ranges (ie. 0-5V) you could also set the CV bit (Clear Voltage) to 00 and apply a /CLEAR pulse. 

Best regards,

Ian

My design is using bipolar power supply to generate bipolar output. Can I just turn off VDD and VSS to turn off the output?

Turning VDD and VSS off while running is not recommended since it may cause damage to the part or other circuits connected to it. 

What you can do is a Hardware or Software Reset which will reset the output to power-on default which is with a 1k ohm pull-down to gnd. 

When you want to turn it on again, just reconfigure the output range and output value.