LM2903B-Q1: Unpowered Inputs

ReedKacz

Part Number: LM2903B-Q1
Other Parts Discussed in Thread: LM2903B, LM2903, LM339

Hi - customer question below:

If 13.5V is applied through 49.9kOhms to the (+) input of a LM2903B that has no power applied to it (VCC=0V), is there any kind of positive-voltage clamping diode on that LM2903B (+) pin that would try to conduct some current to VCC? Or does that input not have any clamp on it for positive current?

Thanks!

Reed

over 1 year ago

+1 Chi Nguyen1 over 1 year ago

TI__Genius 11621 points

Hi Reed,

Thanks for reaching out. No, LM2903B does not have any positive voltage clamping diode. The inputs can be taken up to 36V, regardless of supply voltage, even V+ = 0V, so no damage will occur for this condition.

+1 Paul Grohe over 1 year ago

TI__Guru 51156 points

Hello Reed,

No. There is no upper clamp on the LM2903. The input stage reverse biases and turns off when ~1V below V+. Next stop is device avalanche breakdown.

See the LM339 family appnote:

Application Design Guidelines for LM339, LM393, TL331 Family Comparators

If the source voltage goes above 36V, then external clamping will be required.

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LM2903B-Q1: Unpowered Inputs