AD215: more current through V+ ISO than 10mA specified in the datasheet? is this possible - while V- ISO has no load?

Document created by analog-archivist Employee on Feb 23, 2016
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We are currently designing an electronic circuit in which we need an
isolation amplifier and we are really interested in using the AD215
since it implements an isolation amplifier with an output range of +/-
10V and have in the same time a built-in isolated isolated power supply
of +/-15Vdc @ +/-10mA.
For our application, the circuit connected to the isolated power supply
will request more than +10mA. Actually, the final current consumption
will be between 12 and 20mA. But only the V+ ISO will be loaded,
nothing will be connected to V- ISO.

 

I believe this will be OK although we do not guarantee this in our datasheet.

I configured a module with a 650 Ohm load (slightly over the 20mA desired) on
the +Viso supply and the following is what I observed no load to 650 Ohm load:
• Power supply current increased by about 25mA.
• The +Viso supply dropped by about 800mV
• The ripple on the +Viso power supply increased by about 60mV
• The offset of the module shifted by about 2mV
• The gain error changed slightly.
• The temperature of the case increased. Observed by touching the case with
fingers.

I do not know how the MTBF compares between this configuration verses a 10mA
load on each Viso supply.


additional update:

The module continued to operate as it did last night.
I also discovered that the test card I used for this testing also had a load
configured on the Viso supplies as well as additional bypass caps. The test
card already had a 10mA load configured on both the + & - Viso supply, so my
testing was based on adding an additional 20mA load on the +Viso supply
resulting in a 10mA load on the –Viso supply and a 30mA load on the +Viso
supply.

Given these results I think the customer should not have a problem; however we
do not guarantee the performance under these conditions.

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