CCS/OPA4140: OPA4140 overcurrent

Derrick

When you say input current I assume you mean supply current. The only way you could get that type of current on the opamp inputs is to have an input signal exceed the supply voltage which would forward bias the ESD diodes.

Your circuit may be oscillating. Look at the outputs of each of the amplifiers with an oscilloscope.

Regards
Dennis

Your op amps by inspection are not stable. See the following for stability information:
training.ti.com/ti-precision-labs-op-amps
10. TI Precision Labs - Op Amps: Stability
In addition consider downloading the free SPICE simulator from TI, TINA-TI at:
http://www.ti.com/tool/tina-ti
By building and simulating your circuit in TINA-TI many problems can be avoided before building it in the real world. If you have problems once the circuit is built in TINA-TI feel free to post the schematic from TINA-TI on the E2E Forum for further assistance.

Dear Green,

Thanks so much for your information. I built the model in TINA-TI. But the ERC always told me the invalid device. Can you help me resolve this problem? thank so much.

Best regards,

Derrick

1881.Noname.TSC

Dear Dennis,
Thansk so much for your reply. Actually, the input signal between pin 3 and pin 5 is NC. hence the input signal is 0 and the supply current is still very large. I can not find the reason. can I change the OPA4140 to another chip to resolve this problem?

I changed the OPA140 to OPA137. the circuit works and the output waveforms look good with the 50 Hz sine input. It looks like the op amps are stable.
But practically the OPA 4140 will be very hot due to the overcurrent. Once I removed the OPA4140 from the PCB board. everything is fine. I checked that the pins connection are good and not shorcircuit.

If you study the recommended material you will find the circuits are not stable with OPA140 but will be stable with OPA137. Your resistor values of 1MEG are very high and you will have large noise in your circuit. A capacitor right on the output of the op amp is NEVER a good idea.
Your design can all be done by simulation to prove correct operation. You can model ADC input and make sure op amp settles at the end of the ADC acquisition time.
What signal connects to the discrete instrumentation amplifier you built? Sensor? What voltages are you reading differentially into these inputs? What common mode is on these inputs - a bridge sensor?

Look at the following:
training.ti.com/ti-precision-labs-op-amps
10. TI Precision Labs - Op Amps: Stability
training.ti.com/ti-precision-labs-adcs