LM2904-Q1: LM2904 PIN 5 is short-circuited to ground

ian wu

Part Number: LM2904-Q1
Other Parts Discussed in Thread: LM2904

Tool/software:

The schematic diagram is shown as follows. This is a temperature sampling circuit for the gun head of one charging gun. The actual main control board has four such circuits. This is the temperature sampling design for the charging gun head. Fault phenomenon: The PIN5 of the LM2904 operational amplifier chip is prone to damage. After testing the ground impedance, a short circuit was found. Please help check where the design is wrong and offer suggestions for improvement. Thank you

1 month ago

0 Raymond Zhang1 1 month ago

TI__Guru* 77521 points

Hi Ian,

ian wu said:
The PIN5 of the LM2904 operational amplifier chip is prone to damage.

I am not sure what the circuit is trying to do. If you want to regulate and filter 3.3Vdc rail, there are better ways to accomplish that.

The circuit seems to taken difference of 3.3Vdc and level shift by another 3.3Vdc with dual RC LPFs to attenuate the ripple noise and double the 3.3Vdc rails. I am not sure what is the temperature sensor is doing at the output of the circuit.

Here is an example how to drive RTD circuits.

https://www.ti.com/lit/an/snoaa67a/snoaa67a.pdf?ts=1756036440204

https://www.ti.com/lit/an/sbaa275a/sbaa275a.pdf?ts=1756012583671

https://www.ti.com/video/6330515840112

https://www.ti.com/lit/an/slyt442/slyt442.pdf?ts=1756046216621&ref_url=https%253A%252F%252Fwww.google.com%252F

For a difference amplifier, you need to have stable, low impedance and fixed reference voltage on the non-inverting pins, see the simulation. If you want to double the supply rail of 3.3Vdc, there are better ways to do this. Please clarify what you are trying to do.

LM2904-Q1 Diff Amplifier 08242025.TSC

If you have other questions, please let us know.

Best,

Raymond

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LM2904-Q1: LM2904 PIN 5 is short-circuited to ground