Update timestamp only if partial update changes other fields

Hi, I am making a partial update on a document and I'd want to update a corresponding timestamp field only if any of the other fields defined in partial update have changed.
If I explicitly set timestamp field to "now" as part of partial update, document will always be updated, but I'd like to update the document only when any field, other then timestamp, has been updated and otherwise perform a no-op.

Is it possible to do so with partial update?