LM7301: about V+ pin negative voltage before power is applied

Joyce Li

Part Number: LM7301
Other Parts Discussed in Thread: LM7705

Hi dear expert,

My customer has adopted LM7301 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 LM7301 and damage or cause any issue to LM7301?

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 kai klaas69 over 3 years ago

Guru 140200 points

Hi Joyce,

is the input current limited to 10mA maximum, as mentioned in section 6.1 of datasheet?

Eventually using the LM7705 is a remedy.

Please show a schematic.

Kai

0 Tim Claycomb over 3 years ago

TI__Genius 15410 points

Hi Joyce,

Is V+ the non-inverting input pin or the positive power supply pin? The datasheet labels the power supply pin as V+.

Thank you,

Tim Claycomb

0 Joyce Li over 3 years ago in reply to Tim Claycomb

TI__Intellectual 2170 points

Hi Tim,

thanks for your reply, V+ means the positive power supply pin.

Thank you!

Joyce

0 Tim Claycomb over 3 years ago in reply to Joyce Li

TI__Genius 15410 points

Hi Joyce,

The V+ (positive supply) pin cannot go below the V- (negative supply) pin, otherwise, damage may occur. When the V+ pin goes negative, is the V- pin at a higher or lower voltage than V+? Can you provide scope shots of both the V+ and V- waveform?

Thank you,

Tim Claycomb

0 Joyce Li over 3 years ago in reply to Tim Claycomb

TI__Intellectual 2170 points

Hi Tim,

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.

+1 Tim Claycomb over 3 years ago in reply to Joyce Li

TI__Genius 15410 points

Hi Joyce,

As long as the positive supply is not at a lower voltage than the negative supply at any time there should not be an issue. If the positive supply is lower than the negative supply, this would mean the device is seeing a negative supply voltage (Vs = V+ - V-) which will damage the device.

Thank you,

Tim Claycomb

0 kai klaas69 over 3 years ago in reply to Joyce Li

Guru 140200 points

Hi Joyce,

looks like this latch-up trap:

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/957524/opa2990-about-powerup-sequence/3539257?tisearch=e2e-sitesearch&keymatch=latch-up%252525252520AND%252525252520kai#3539257

Kai

0 Joyce Li over 3 years ago in reply to Tim Claycomb

TI__Intellectual 2170 points

Thanks a lot Tim!

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LM7301: about V+ pin negative voltage before power is applied