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ChRe_4711096
Level 4
Level 4
50 replies posted 25 replies posted 25 sign-ins

I found that an LPComp gave me correct results with a common mode voltage below ground. The datasheet clearly states that the input voltage range does not extend below ground - but in practice, how bad is it to use it down there, within the clamping diode range?

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Vasanth
Moderator
Moderator
Moderator
250 sign-ins 500 solutions authored First question asked

Hi,

The device is guaranteed to work as limits set in the datasheet. Even though you could see the output below the range, it is not guaranteed. Regarding the second question, yes. The device absolute maximum are the limits the voltage can go. For GPIO pin,-0.5V( VGPIO_ABS,SID3 in datasheet) is the minimum voltage the device can with stand. One more point to add here is going beyond these absolute maximum limit can affect the device reliability.

Best Regards,
Vasanth 

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3 Replies
Vasanth
Moderator
Moderator
Moderator
250 sign-ins 500 solutions authored First question asked

Hi,

The device is guaranteed to work as limits set in the datasheet. Even though you could see the output below the range, it is not guaranteed. Regarding the second question, yes. The device absolute maximum are the limits the voltage can go. For GPIO pin,-0.5V( VGPIO_ABS,SID3 in datasheet) is the minimum voltage the device can with stand. One more point to add here is going beyond these absolute maximum limit can affect the device reliability.

Best Regards,
Vasanth 

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Len_CONSULTRON
Level 9
Level 9
Beta tester 500 solutions authored 1000 replies posted

ChRe,

As Vasanth stated, operating an input below VSS is not preferred.  Besides not getting the desired results it could lead to long-term damage to the IC.  This is especially true if the current into the the input exceeds the "latch-up" current.  This is where the voltage is such where it forward biases the lower clamping ESD diode and melts it.

You stated:

I found that an LPComp gave me correct results with a common mode voltage below ground.

The internal LPComp probably see little of the voltage when it is below VSS.  Besides, the clamping diode will try to limit the voltage to -0.5V.

Len
"Engineering is an Art. The Art of Compromise."
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My external circuitry limits the current through the clamping diode to an acceptable value within the absolute maximum rating of the device. Also, the common mode voltage will not be below -250 mV.

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