Part Number: TLV3691
My customer is using the TLV3691 as a comparator to monitor the voltage from a Potential transformer (PT). The negative input of TLV3691 is connected to the PT output and the positive input of TLV3691 is connected to a reference voltage. When customer is doing the test, they found that the input impedance of the negative input is abnormal. The input impedance is only several ohms instead of several Mega ohms. I already checked with customer that the negative input voltage is within the range from GND to VCC. Do you have any comment on what may be the reason of this input impedance issue?
In reply to Jian Zhang5:
please see the schematic as below. The PT outputs a current signal and then converted to a voltage signal by a 80 ohm resistor. Customer found that during the test, the voltage on the 80 ohm resister is lower than the normal value. So they measured the input impedance of the negative input and found that the impedance is abnormal. There' are two TLV3691 on the board and both of them have the same issue. For one TLV3691, the negative input is measured as 80 ohm. For the other TLV3691, the negative input is measured as 50ohm. The measument is done by multimeter. Do you have any comment what may cause the input impedance issue?
In reply to Wayne Wang20:
TLV3791 has a maximum input bias current of 20nA which is equivalent to 100s of MOhms input impedance. If the customer is seeing a solid resistance measurement of input in both directions, most likely the input is a melted junction (short). In this case, the device in question is most likely damaged. There is a thread elaborating in details over a similar issue:
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