LMC6772: will the device break when IN+ is 3.3V and no power is applied to V+?

Howard Zou

Genius 12365 points

Part Number: LMC6772

Hi,

my customer observed when 3.3V is applied to IN+ through 240kOhm, the voltage on IN+ is only 0.6V, when V+=0V.

Why IN+ is so low? Are there any diodes from IN+ to GND and V+ inside the device?

Will the device break at this situation?

over 4 years ago

0 Chuck Sins over 4 years ago

TI__Mastermind 23425 points

Howard

There are protection diodes to V+ and V- on the inputs. So if you ground V+ as you described, you will see a conducting diode if you apply a voltage to the input.

Since the current is being limited by a 240k resistor, no damage to the device will occur.

Chuck

0 Howard Zou over 4 years ago in reply to Chuck Sins

TI__Genius 12365 points

Chuck,

thank you.

So what's the current rating of the diodes inside? I should use this value to calculate the resistor to limit the current.

0 Chuck Sins over 4 years ago in reply to Howard Zou

TI__Mastermind 23425 points

Howard

You should limit to less than 5mA when the input voltage is going to exceed V+ or V-.

Sorry for not mentioning that in the previous response.

Chuck

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LMC6772: will the device break when IN+ is 3.3V and no power is applied to V+?