6

Application information

6.1

Overview

TSC21x series are specially designed to accurately measure current by amplifying the voltage across a shunt

resistor connected to its input. This voltage drop Vsense, is then amplified by an instrumentation amplifier

providing a max. input offset voltage of 35 µV (25 °C) for an input common voltage of 12 V for gain higher than

200.

TSC21x series with the use of thin film resistor and zero-drift architecture, offer an extremely precise input offset

voltage, gain error and very high CMRR performance even in high frequency range. Moreover, thanks to the

possibility to fix the output common mode voltage, the TSC21x can be either used as unidirectional or

bidirectional current sensing amplifier.

TSC21x provide an extended input common range from ground, and up to 26 V allowing either low-side or high-

side current sensing, while the TSC21x devices can operate from 2.7 to 26 V.

The parameters are very stable in the full VCC range and several characterization curves show the TSC21x

device characteristics at 5.0 V. Additionally, the main specifications are guaranteed in extended temperature

ranges from - 40 to 125 °C.

6.2

Theory of operation

The main particularity of the TSC21x is the ability to work with input common mode voltage largely beyond the

power supply Vcc range.

•

Vicm > 2.5 V

In this case, the power supply of the TSC21x is issued from the input and not only from the Vcc power supply.

More precisely a current is drawn from the common mode rail as depicted in Figure 28 to power it.

Figure 28. Power supply when Vicm > 2.5 V

OUT

VREF

V

Shunt

resistor

In-

In+

R1

R2

R3

Gnd

R4

-

+

CC

In Figure 29 we can see that the current used to power the TSC21x is increasing with the Vicm voltage. The slope

is representing the internal common mode resistances. Part of it being Vicm / (R4 + R1) and part of it serving to

supply the input stage of the circuit, roughly 20 µA.

So due to the architecture of the TSC21x the current to be measured through the shunt resistor must be much

larger than the input bias current. In case of small current to measure the Iib, current must be taken into account.

TSC210, TSC211, TSC212, TSC213, TSC214, TSC215

Application information

DS13237 - Rev 7

page 12/38