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MM912J637 Vsense input current causes ~40mV offset error

Question asked by Ian Wilson on Sep 8, 2014
Latest reply on Oct 7, 2014 by Alexis Adenot

Hello all,

 

We are using the MM913J637 device.

 

The data sheet specifies a 2.2kohm resistor on the Vsense input (for over voltage protection).

 

The data sheet does *not* specify any input leakage current or resistance for the Vsense input. (The data sheet mentions nothing about this.)

 

With a 12V input I measure about 40 mV drop across the 2k2 resistor (so about 16 uA). This varies slightly but linearly with voltage. At Vin=10V it is about 30mV, at 18V it is about 54mV. I have not measured how it varies with temperature.

 

This seems like a *large* offset error given the other analog specs are much tighter than this.  There is no mention of this in the data sheet nor of the need to apply any sort of scaling correction.

 

I assume it is related to the fixed 1/28 voltage divider on the Vsense input but there is no info on what the input looks like. It would appear to be equivalent to about 735 kohm.

 

What is the architecture of the Vsense input?

 

Is there any information about how the input current will vary with temperature?

 

Can the value of the protection resistor be lowered to reduce the offset error?

 

Thank you for any comments,

Ian

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