Will the AD5420 performance meet the specifications under the following conditions?
External Reference 5V
( Can the External Reference be more than the digital supply? )
The AD5422 doesn’t have trim pins like the AD420 so it cannot be trimmed like the AD420. If further trimming is required, it needs to be done in the firmware. On power up the part runs an internal calibration routine, so the user doesn’t need to do any calibration, they just need to wait for 40µs after a successful power-on reset.
Looking at the abs max ratings of the part, there are no dependencies to both supplies. I don't see any problem with the external reference being higher than the DVCC pin.
Looking at the DAC architecture, the reference will be used to dictate the amount of current on each leg of the ladder while the DVCC will be controlling the states of the switches.
Hope this answers your question.
Thanks for your reply. I have one more query:
How does one calibrate the span and zero of an individual converter with external trimpots?
My previous experience with AD420 (internal reference) is that it requires external trimpots to set span and zero when precision is required.
The customer is comfortable with this procedure.
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