AN4366

How to compensate the input offset voltage

DocID025330 Rev 1

7/14

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How to compensate the input offset voltage

The input offset can be compensated and output saturation can be avoided thanks to:

•

an external current source

•

added resistances

To realize this compensation, it is recommended to use the TSC1031 rather than the

TSC103. Both devices are very similar in terms of their electrical characteristic, but the

TSC1031 is a more flexible current sensing solution as it allows the Rg internal resistors

values to be externally changed.

The main objective is to compensate the input offset by creating an opposite voltage,

VosC, thanks to an Rs2 resistance and a current source. In order to compensate the native

Vos, it is important that: (-Vos + Vosc + Vshunt) * Gain > Vol.

Figure 4 shows the architecture where the current sensing device always has a negative

input offset. The current source is made of few components: a voltage reference (TL431),

an op-amp (LMV821) which is used as a buffer, a NPN transistor, and one resistor (Rc4).

Figure 4: Schematic to compensate Vos

Current source

5V

5V

Vref

TL431

Rc4

Vshunt

Rs1

Rs2

Vosc

Vos

Rin1

Rin2

5k

Ω

5k

Ω

5V

Vout

Rg

125k

Ω

Rs3

Rshunt

Rin1

Rin2

5k

Ω

5k

Ω

Rg

125k

Ω

+

-

+

-

TSC1031

+

-

LMV821

K1

K2