MSK3002 datasheet(4/6 Pages) MSK

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USING CURRENT SENSING MOSFETS:

A MOSFET transistor is constructed of many individual MOSFET cells connected in parallel. They share the current total

very evenly. If one of these cells are brought out to a pin, that cell will pass an accurate proportional amount of the total

current. This current can be used as a low power sense of the whole current without passing that whole current through a

sensing device like a resistor. This small current multiplied by the ratio specified on the data sheet equals the whole current.

There are several methods of working with the sense function to obtain the actual current.

1. Virtual Earth Sensing

The disadvantage is amplifying a current swing of 10 amps in 100 nSec to produce a 5V output means the op amp has to

slew 50V/µSec. This is beyond the capabilities of a lot of op amps.

2. Resistor Sensing

The disadvantage is RT voltage must be above the offset voltage of the op amp and RT must be much less than RDS(ON) of

the sensing cell or temperature shifts will affect accuracy.

Rev. C 7/00

APPLICATION NOTES, CONT.

MSK3002 Datasheet(PDF) 4 Page - M.S. Kennedy Corporation