AN4366

Saturation problem

DocID025330 Rev 1

5/14

2

Saturation problem

If the TSC103 is used in single supply with a positive Vos (see Figure 2 in Section 1:

"Definition of input offset voltage (Vos)") and zero current through the shunt, it becomes

saturated and the output is clamped to the Vol. Unfortunately, this phenomenon also holds

true with a positive Vos and low current. In such a case, a voltage drop through the shunt,

lower than the Vos of the current sensing, gives an incorrect output value.

Let us consider an automotive application where it is necessary to sense the current of the

battery. The minimum current that must be measured is 1 A. To limit the power dissipation,

a 0.5 mΩ shunt resistor is used. The current sensing, TSC103, powered in single supply

and set with a gain of 100 is used to measure the current (see Figure 3).

Figure 3: Current sensing single supply

The native input offset of the TSC103 might be, in the worst case, +1.1 mV or -1.1 mV, and

the maximum Vol might be 125 mV. The output voltage of the TSC103 is given by

equation (2):

To obtain a valuable measurement, the Vout must be higher than the output stage,

low-state saturation voltage i.e. Vout > Vol.

Ibattery

Vcc

1A

Rshunt

Vos

0.5 m

Ω

Gnd

+

-

TSC103

Gain x100

.Gain