The transition between amplifiers A1 and A2 can also be observed on a dynamic signal, when the common mode

voltage varies around a Vicm = 40% VCC.

5.3

Rsense selection

The selection of the shunt resistor is a tradeoff between dynamic range and power dissipation.

Generally, in high current sensing applications, the focus is to reduce the power dissipation (RI²) as much as

possible by choosing the lowest shunt value. It is quite easy if the full-scale current to be measured is low.

In low current application, the Rsense value could be higher to minimize the impact of the offset voltage of the

circuit. Keep in mind that due to the input bias of several µA the TSC20x cannot measure current in the same

range.

The tradeoff is mainly when the dynamic range of current to be measured is large, meaning there is an ability to

measure with the same shunt value low current to high current. Generally, the current full scale Imax defines the

shunt value thanks to the full output voltage range, the gain of the TSC20x.

At first order, the full current range to measure through Rsense can be defined by equation 3, just by taking the

gain error and input offset voltage as inaccuracy parameters:

Isense_full_scale*Rsense= Vcc−250mV

TSC_Gain1+Eg

− Vio

(3)

Its purpose is to highlight that the product Rsense * TSC_gain is determined by the application, and that once one

of these two parameters is selected, the maximum value of the second one can be calculated.

5.4

Input offset voltage drift vs. temperature

The maximum input offset voltage drift vs. temperature is defined as the offset variation related to the offset value

measured at 25 °C. The signal chain accuracy at 25 °C can be compensated during production at application

level. The maximum input voltage drift vs. temperature enables the system designer to anticipate the effect of

temperature variations.

The maximum input voltage drift vs. temperature is computed using equation 4.

ΔVioΔT

=max VioT−Vio25°C

T−25°C

(4)

Where T = -40 °C and 125 °C.

The TSC20x datasheet maximum value is guaranteed by measurements on a representative sample size

ensuring a Cpk (process capability index) greater than 1.3.

5.5

Error calculation

The principal sources of errors such as input offset voltage, gain error, and common-mode rejection ratio are

described separately in the electrical characteristic section. This chapter summarizes the most important errors to

take into account during a design phase.

•

Input offset voltage error

Equation 5 depicts a first order error calculation taking into account the input offset voltage. In an environment

with unstable temperature, it is important to consider the deviation of the Vio. The error linked to the input offset

on the output voltage can be written as equation 5:

Vio Error= ±Vio± Dvio/DT*ΔT*Gain

(5)

•

Gain error and shunt resistance accuracy

Gain error=Gain1+εgain

(6)

Rsense error=Gain1+εRsense

(7)

Where Ɛgain is the gain error 2% max for the TSC20x.

Where ƐRsense is the shunt resistance error. Shunt resistors from 5 mΩ to 100 mΩ are available within 1%

accuracy or better.

TSC200, TSC201, TSC202

Rsense selection

DS13882 - Rev 2

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