TL084A: Opamp operated outside of common mode range

Andrew Massey

Part Number: TL084A
Other Parts Discussed in Thread: TL084, TL081H, TL084H

Hi,

Hi,
To what current, if any, would the attached current clamp regulate the current, given that it is being operated outside of its common mode input range?
LTspice and jpeg attached.
The opamp is actually a TL084A

TL084 family datasheet
https://www.ti.com/lit/ds/symlink/tl084h.pdf?ts=1692381297170&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTL084H

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 276380 points

The files are not attached.

Outside the valid common-mode input range, correct operation is not guaranteed. If both inputs are outside the range, the device cannot correctly determine the differential input voltage at all, so the output might saturate as far as possible to the positive or negative supply.

0 Andrew Massey over 1 year ago in reply to Clemens Ladisch

Prodigy 150 points

My apologies, please find here the schem

0 Clemens Ladisch over 1 year ago in reply to Andrew Massey

Guru 276380 points

The datasheet says that the common-mode input voltage range typically goes up to V+. So I'd expect the worst that would happen is that the electrical characteristics are not met, i.e., that the offset voltage could be somewhat larger than 6 mV.

Just use the TL084H (or TL081H for a single channel) instead, which is guaranteed to go up to V+ (and is cheaper, and has a smaller offset voltage).

0 Ron Michallick over 1 year ago in reply to Clemens Ladisch

TI__Guru*** 147826 points

Andrew,

TL084H will be a better choice not only based on input voltage. Output voltage range will be better on TL084H.

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TL084A: Opamp operated outside of common mode range