AD9832: Seperated DGND and AGND

Document created by analog-archivist Employee on Feb 23, 2016
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I work on the AD9832 evaluation board and I’d like to have two different
voltages for Dgnd and Agnd (0.5V offset between the two power supply).
But on the evaluation board the Agnd and the Dgnd seem to be connected.

Where are they connected and how can I disconnect Agnd and Dgnd on this board?

 

The Absolute maximum rating s for AD9832 (on age 4 of the datasheet) state that
AVDD and DVDD must be within 0.3V. This is usually because of parasitic or
protection diodes which join AGND and DGND internally. If you exceed 0.3V
between, the internal diodes turn on and a lot of current will flow in the
AD9832 suubstrate, causing heat generation, device malfunction and a possibly
destructive latchup situation. I recommend that AGND and DGND always be
connected to the same potential, and if this is not possible, connect the AGND
and DGND traces with schottky diodes in anti-parallel configuration.

On most converter evaluation board the AGND and DGND planes would normally be
connected immediately under the device and you can usually see this connection
on the reverse of the board. You can cut this connection if you really want to,
but I would strongly recommend against running AGND and DGND at 0.5V
difference.

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