protection for op amp

[yefj]

Hello i am using the following OPAMP in my circuit.
I know i need to put reverse biased diodes to protect my OPAMP.
How do i know what diode exactly can be used in my case?
Also in forward biased the diode has 0.7 voltage drop over it so i should use 5.7V in my power supply to have exactly 5 V on the opamp?
Thanks.
https://www.analog.com/media/en/technical-documentation/data-sheets/AD8031_8032.pdf

 

[yefj]

Hello, i am using the following OPAMP in my circuit.
I know i need to put reverse biased diodes to protect my OPAMP.
How do i know what diode exactly can be used in my case?
Also in forward biased the diode has 0.7 voltage drop over it so i should use 5.7V in my power supply to have exactly 5 V on the opamp?
Thanks.
https://www.analog.com/media/en/technical-documentation/data-sheets/AD8031_8032.pdf

 

[KlausST]

I know i need to put reverse biased diodes to protect my OPAMP.

You say: " I know...".
But how do you know?
You want to protect the OPAMP, I guess ... but from what do you want to protect it?

Klaus

 

[dick_freebird]

Not sure why, or why you think you "know" you need reverse biased
diodes. If you are thinking about a classic minimal input rail-pair clamp,
an op amp of that generation might well have some built in that can
meet your assembly's ESD threat. Have to dig for that, or do some
bench abuse to find the ditches on either side of the paved road.

So go ahead and enumerate that threat package and what you need
to be able to sell the story. Include what you can find about the op
amp internals (usually the input network will be shown somewhere
in the back pages of the datasheet, or the first app note). Then make
with the analysis by various means, to see where you are and where
you have to be, and onward to the answers you are asking for.

 

[barry]

I don't understand any if this. Why do you need reverse biased diodes? To protect it from what? Thieves? ESD? Overvoltage? On the input? If so, why do you need to raise your supply one diode-drop?

 

[FvM]

Also in forward biased the diode has 0.7 voltage drop over it so i should use 5.7V in my power supply to have exactly 5 V on the opamp?

Completely wrong consideration.
For clarification:
- show a schematic of the intended protection circuit
- what's the expected overvoltage source and voltage range you want to protect against
- did you notice that specifically AD8031 should be protected against differential input above +/- 3.4V?

 

[stenzer]

Hi,

what is your aim, are you worried about ESD?

The datasheet mentions "Sustained input differential voltages greater than 3.4 V should be avoided as the input transistors can be damaged. Input clamp diodes are recommended if the possibility of this condition exists."

So here you are interested in limiting your input voltage to 3.4 V, and an increase of the supply voltage to 5.7 V does not protect your input, if this voltage is also used as your clamping-diode's cathode voltage.

Have a look here https://www.analog.com/en/technical-articles/differential-opamp-driver-protects-a-highresolution-adc-from-input-overvoltage.html

BR

 

[dick_freebird]

Cross-strapped Schottkies on the input pins would deal
with the differential abs max limit. That is below the supply
limits and the single ended input range, so ordinary rail
ESD network would not help.

"Back in the day" you'd see high speed op amps with
limited input differential range, incorporate differential
protection (internal diodes across the front end).

If limiting input difference to ~ 300mV costs you anything
(like max slew rate, from limiting overdrive) you could
use low-C fast recovery PN or anti-parallel series Schottkies.
But really that much differential voltage ought to fully steer
a diff pair.

Now, the single ended limit for an input voltage and
whether that's handled by designed internal ESD clampage,
remains an open question.