Maximum voltage of isolated power output

Document created by analog-archivist Employee on Feb 23, 2016
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Hello,

we plan to use AD215 part in our next design. I have a question related to a
maximum output voltage of the isolated power supply. The data sheet states a
maximum no-load output of isolated power supply is +/-17.25V at typical
conditions (as I understand +25oC), then it provides a positive coefficient of
the isolated power supply output as +20mV/oC.

Do I understand correctly that at +85oC the maximum output voltage can be as
high as:
17.25V+20mV*(85oC-25oC)=18.45oC

Can anything else influence the output voltage of the isolated power output of
the AD215 (increase it), like e.g. a power supply higher than +/-15V. AD216 can
accept input power supply +/-16.5V what is 1.5V higher than the nominal 15V.
Line regulation is defined as typical 290mV/V (no sign is specified in the data
sheet) so the increase would be 1.5V*290mV/V=453mV

The total worst case is then
17.25+1.2V*0.435V=18.885V

Do I understand the specification correctly?

We plan to power another AD part from the isolated power supply of the AD215.
The part is AD8253 and the absolute maximum supply voltage of it is +/-17V. Can
the AD8253 be safely powered from the AD215  (directly)?

 


The maximum voltage of the isolated power output is specified in the
www.analog.com/AD215 datasheet to +/-17.25V at a temperature of 25°C. For
temperatures differing from 25°C the maximum output voltage changes. The
value,"vs. Temperature", given in the Specifications table of the datasheet is
a typical (Typ) value. This value is not guaranteed by Analog Devices, but
gives you an impression of the typical variation per degree Celsius.
ADI guarantees only maximum and minimum values in the Specifications section of
the datasheet.

The AD8253 is specified for a supply voltage of +/-15V in the Specifications
section of the www.analog.com/AD8253 datasheet. The Absolute Maximum Ratings
for the supply voltage are given as +/-17V. Please remember, that the Absolute
Maximum Ratings are "a stress rating only; functional operation of the device
at these or any other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute maximum
rating conditions for extended periods may affect device reliability. "
For your reference I am attaching a screenshot of the Absolute Maximum Ratings
section of the AD8253 below.

Thus, powering the AD8253 from the AD215 directly might damage the parts.
However, you could consider adding a couple (or few) of diodes in series with
the isolated power supplies to drop down the voltage to a lower level.

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