LMC7101: about power V+ pin

Joyce Li

Part Number: LMC7101

Hi dear expert,

My customer has adopted LMC7101 and they have below question: the V+pin will have -0.3V~-0.4V voltage drop for a while before the power is applied. Will this impact LMC7101 and damage or cause any issue to LMC7101?

The figure below shows the power-up timing of the V+ pins. From the figure, it can be seen that the yellow waveform represents V+. A power-down pit appears before the power is applied, so please help evaluate if there is any impact.

Thanks very much for your support.

Joyce Li

over 3 years ago

0 Ron Michallick over 3 years ago

TI__Guru*** 140026 points

Joyce,

Are any inputs shorted or low resistance (to ground or any other voltage)? What is the voltage at the output pin during this time?

0 Joyce Li over 2 years ago in reply to Ron Michallick

TI__Intellectual 2170 points

Hi Ron,

thanks for your reply. Inputs are fine. The V+ pin is the positive power supply pin, not the non-inverting input pin.

0 Ron Michallick over 2 years ago in reply to Joyce Li

TI__Guru*** 140026 points

Joyce,

Is the V- pin ground or some other voltage?

0 Ron Michallick over 2 years ago in reply to Ron Michallick

TI__Guru*** 140026 points

By the way, does the green signal connect to op amp other than just the V+ (power) pin?

0 Joyce Li over 2 years ago in reply to Ron Michallick

TI__Intellectual 2170 points

Hi Ron,

thanks very much for your reply! Actually the waveform i provided in the beginning has both V+(power supply) and V- (power supply). The yellow curve is the V+, the green curve is V-. After V- powers on, it is -5.2V. The V+ drops to -0.4V and stay a while until V+ is on. Will the negative voltage appearing on V+ affect the V+ pin and device?

Thank you very much.

0 Ron Michallick over 2 years ago in reply to Joyce Li

TI__Guru*** 140026 points

Joyce,

The op amp supply is V+ relative to V-. In the entire waveform V+ is greater than V- so the op amp has a normal positive (total) power supply. You stated the inputs are fine, so I take your word on that.

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LMC7101: about power V+ pin