OPA657: Simulation error

Allen Du

Part Number: OPA657
Other Parts Discussed in Thread: OPA656, TINA-TI

Hi Team,

I plan to build a circuit to measure 400VDC pulse, to measure the exact voltage of the pulse, I am trying to use OPA657 to simulate, when there is only one OPA657 in the circuit, the pspice can run simulation, but when there are 2 OP657 in the ciurcuit, simulation cannot run and says "there are no data values in section number 1 ignoring this section". when i change to other low speed OP-AMP, no this issue. I need a op-amp with high speed, high input impedance and low input bias current.

Could you have a look what's the reason. Attached the circuit and pspice file for your referrence.

Buy the way, in this circuit I don't use isolator, just use high value resistor divide 400VDC and get a low voltage common input to OPA657, is it safe for the OPA657 input? Thanks in advance.

.OPA657.zip

over 2 years ago

+1 Michael Steffes over 2 years ago

Guru 48385 points

Morning Allen,

Sim issue aside, you are essentially doing a high impedance probe, need to set up your speed up caps across the passives correctly to retain response flatness to the amp inputs. It looks like the amps are set up for low gain, the OPA657 is not stable at low gain, a quick substitute would be the OPA656.

These JFET parts are good for high source R, and alternates would be available but would need the speed requirements and I/O voltage needs to set supply ranges.

0 Allen Du over 2 years ago in reply to Michael Steffes

Prodigy 250 points

Hi Michael,

Thanks for your help, I tried add caps on the resitors, but the output singal has spike, attached picture are with/ whithout caps.

And OPA656 has the same issue, simulation can run when only 1 OPA656, but failed when there are 2 OPA656 in the circuit, could you hlep have a look, thanks again.

OPA656 TEST2.zip