Hi,
I have the following circuit which uses the high speed comparator LT1713:
It forms a current trip circuit, on the non inverting input I have a Rogowski coil connected to the BNC. On the inverting input there is a reference voltage from a DAC.
In my current setup the feedback resistor is removed and the chip is being powered from a 12V rail, which should be fine according to the datasheet.
The problem I am experiencing is that the non inverting pin has an offset of approximately +200mV when the Rogowski coil is connected and measuring 0 amps, when removed the offset increases to ~500mV. This offset is also effected by the reference voltage on the non inverting pin, but is still present when the ref is 0V.
I can get rid of the offset if I fit a 50 ohm terminator to the BNC connector, the output resistance of the Rogowski coil should be 50 ohms so I am a bit surprised it cannot pull down this offset on its own.
The offset is always there when the the Rogowski coil is measuring and stays there when the two inputs are very close - I did suspect it was a drop across some protection diodes between the two inputs.
Does anyone have any advice on how I can get rid of the offset? Is it expected for the inputs to float without a strong pull down? As you can see i have a 1Meg pull down at the moment, this could be reduced further but the Rogowski coils need to drive at least 100k which I suspect will not be enough to get rid of this offset.
Thank you for any help you can offer.
Josh
