ADUM 3190 Impendace problem

Hello,

we used the evaluation board to test the ADUM 3190. The image on the left side shows the input cirquit of the ADUM 3190.

We removed the resistors between GND1 and GND2.

It works fine with R=1.5k.

The problem with this low R is the low input impendance. Therefore we increased R to 750k. Our source has an impendance of 71.5k.

With this high R the cirquit is no longer working.

Could that be? What do we overlook.

Regards

Alexander

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    •  Analog Employees 
    on Feb 24, 2020 4:06 AM 9 months ago in reply to Zac

    Hi Zac & Alexander:

    I redraw the schematic as below:

    the relationship between Vout, Vref and Ve is like below:

    When R=750K , the Vout would be  more than 10 times larger than that when R=1.5K.

    We must notice that the voltage range on comp pin is only from 0.2V to 2.7V. by aimplify it 10 times, Vout is probably out of this range. 

    Regard

    Chris