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ADM660 issue on startup

Question asked by Mark81 on Jul 20, 2015
Latest reply on Jul 21, 2015 by KRZ

Hi!

In the schematic attached there is the power section of my board. On the left there is +12VDC, IC1 provides the +3.3V for MCU. IC2 provides about 5.5V and IC3 generates the negative rail (-5.5V).

It works fine, but there is an issue... if the input voltage rises too slow it seems the ADM660 doesn't start to oscillate (the output is 0V) and sinks a lot of current (over 300 mA).

I mean, if I enable the output from a bench power supply, it's very likely it doesn't work. Instead if I plug-in the connector with the bench power supply already enabled it always works.

 

The Vee is connected only to a low-power op-amp (few mA) but I tried to change this with several models and nothing changes, so I assume the problem is just related to the ADM660.

 

Do you see something wrong in my schematic?

I could put a zener diode in series with the input, in order to increase the lowest voltage to feed the regulators... but I would like to understand where is my fault!

 

I also tried to connect LV to GND - with no chance.

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