Conclusion

AN4366

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DocID025330 Rev 1

7

Conclusion

A current sensing powered in single supply is able to measure low current. However, if the

voltage drop through the shunt is lower than the Vos, it might cause some output saturation

problems. In this case, it is important to compensate the Vos by using external resistances

and a current source.

The resistances must be as low as possible and must be well matched to avoid inaccurate

measurements. The current source must be well dimensioned.

For this kind of compensation, it is important to realize a calibration before starting the

measurement. Firstly, measure the output voltage with a minimum current through the

shunt, and then used this baseline value as a reference of minimum current. Figure 5 is a

suggested schematic to compensate the Vos. It avoids any output saturation for low current

measurements.

Figure 5: Suggested schematic to compensate Vos

Current source

5V

5V

Vref

TL431

2.5V

12.5k

Ω

200µA

10

Ω

10

Ω

2mV

Vos

Rin1

Rin2

5k

Ω

5k

Ω

5V

Vout

Rg

125k

Ω

250

Ω

Rshunt

Rin1

Rin2

5k

Ω

5k

Ω

Rg

125k

Ω

+

-

+

-

TSC1031

+

-

LMV821

K1

K2