OP AMP Latch up
OP AMP Latch up
(OP)
Greetings,
I've been experiencing sparodic op amp failure (shorting the power supplies is one failure) in one of my designs. The op-amp (OPA 2277) is being used as a buffer. I was made aware that it is possible to that the inputs are getting a voltage before the power supply pins are. What is the best approach at handling this. Are there other methods besides using Schottky clamping diodes at the input and supplies?
I've been experiencing sparodic op amp failure (shorting the power supplies is one failure) in one of my designs. The op-amp (OPA 2277) is being used as a buffer. I was made aware that it is possible to that the inputs are getting a voltage before the power supply pins are. What is the best approach at handling this. Are there other methods besides using Schottky clamping diodes at the input and supplies?





RE: OP AMP Latch up
RE: OP AMP Latch up
Good luck
RE: OP AMP Latch up
My problem right now is that the failures are random. Some of the op-amps fail immediately, some after we ship them out, and some none at all.
What would be the best approach to test and fix this problem.
RE: OP AMP Latch up
RE: OP AMP Latch up
you can certainly add stuff to the inputs to protect them, but it would seem to be a bad thing to do to a precision op amp whose claim to fame is low bias and leakage currents .
You could and should make sure that there is a solid signal ground connection between the source and the op amp circuitry.
TTFN
RE: OP AMP Latch up
RE: OP AMP Latch up
Do you have a series termination resistor between the Opamp output pin and the cable?
No, the output of the op-amp is directely connected to the output cable connector.
Are the inputs being driven by something that's powered by a separate and unrelated supply?
The inputs are being driven by a INA118 instrumentation amplifier which is powered by the same power circuitry as the op-amp. The output of the INA118 might be going higher before the op-amp supply pins are being driven.
I would recommend output termination resistors in series with the output cable that match the impedance of the output cable.
The only problem with this is that our customer may decide not to use our supplied cable and supply their own cable of different lenght.
I am also using 100 ohm resistor for my feedback resistor on the unity gain buffer.
Would using a signal line protector be of any benefit, I am thinking of using a device such as the MAX4505
Thanks All, M.
RE: OP AMP Latch up
Below is the old design which I based my current design on.
Notice I ommited C7,R8 on my particular design. Can someone shed light on the purpose of R8,C7 on the below design. BTW the old circuit as far as I was concerned did not have the issue of latching op-amps. The reason I ommited C7 and R8 was to conserve board space since I didn't see the purpose of those components. But I may have assumed wrong.
Thanks.
RE: OP AMP Latch up
It looks like you blew away a major portion of the active filter, as well as blowing away R10, which should be some sort of output damping resistance.
You've turned a multipole active filter into a passive RC followed by a buffer
TTFN
RE: OP AMP Latch up
What would be good source to figure (on the net) out this topology. My electronics book from college didn't have that topology listed. Frankly I could probably calculate everything, but I haven't done that in a while
RE: OP AMP Latch up
As for the filter itself:
http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiveTools/filter/filter.html
Anyway, it would appear that not having R10 would probably cause output oscillation.
TTFN