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LMC662: LMC662AIMX/NOPB is supplied by +/-12V source, (V+ - V-) is larger than maximum rating of 16V

shishiker
Prodigy 90 points
Part Number: LMC662
Other Parts Discussed in Thread: OPA2196, LM6132, OPA2192

Hello,

I just took over an amplifying circuit board with LMC662AIMX/NOPB which is supplied by +/-12V source, it's obvious that the op amp is over stressed according to the datasheet, but had been working well.

Just wondering why this single-supply recommended  op-amp can work under dual power supply and even electrically over-stressed. What damage can occur if continually working like this.

Thanks!

  • Former Member
    0 Former Member

    Hello Yinni,

    You are correct. The datasheet's absolute maximum power supply voltage rating (V+ - V-) reads 16V, meaning the amplifier will be electrically over-stressed, or "EOS."

    To answer your questions, the amplifier is able to work under dual supplies even though the datasheet suggests this part is ideal for single supply operation. This can be verified in the datasheet in the "DC Electrical Characteristics" section under the "Test Conditions" column. Note that our test conditions consider negative supply voltages down to -10 V at the negative rail, with a maximum supply voltage of 16 V. This means the amplifier can work with dual supplies and not just with a negative supply tied to GND.

    When a part operates outside of the recommended operating regions, but within the maximum regions, the device should continue to operate as an amplifier. However, it may suffer performance degradation and fail to meet some specifications. Outside of the maximum ratings of operation, your device may stop working entirely.

    Given that your part is working beyond the maximum ratings, it is quite likely already experiencing performance degradation and may soon fail. This is difficult to predict, although for slight EOS the part will generally degrade over time instead of failing suddenly. A typical symptom of EOS is strange output behavior, such as an output fixed to rail regardless of the inputs, caused by shorting of substrate regions in the chip's die.

    If you need to supply V+ at +12 V and V- at -12 V, I would recommend you try a different part.

    For more information on EOS, consider watching TI's Precision Labs videos on the subject: training.ti.com/ti-precision-labs-op-amps-electrical-overstress-eos-1

  • 0
    TI__Mastermind 49966 points

    Hello Yinni,

    You said "had been working", I assume it finally succumbed.

    24V is well over what I would expect the process to survive. Did you happen to notice a high supply current or if it was getting warm?

    As you saw, it will operate for a while, but operating above Abs Max causes internal degradation to occur. The higher the voltage, the faster degradation will occur. Like rev'ing your car engine over the red line - at some point, it finally gives up. It may seem to be functioning before then, but it's life is "adversely affected'.

    You need to bring the supply down under 15V (±7.5V).

    If you cannot modify the design, then try higher voltage devices such as the LM6132, OPA2192 or OPA2196.