5.4

RSENSE selection

The selection of the shunt resistor is a trade-off between the dynamic range and power dissipation.

Generally, in high current sensing applications, the main focus is to reduce as much as possible the power

dissipation (I²R) by choosing the smallest value of shunt. It could be quite easy if a full scale current to measure is

small.

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

circuit. Due to input bias current of several µA, the TSC2011H cannot measure the current in the same range,

when the common mode voltage overpasses the power supply voltage (refer to section about theory of

operation).

The trade-off is mainly when a dynamic range of current to measure is large, meaning ability to measure with the

same shunt value from low current to high current. Generally, the current full scale (Imax-Imin) defines the shunt

value thanks to the full output voltage range, the gain of the TSC2011H. The TSC2011H can work with a full scale

∆Vout = 100 mV to Vcc - 100 mV with maximum gain accuracy of 0.3%.

At first order, the full current range to measure through Rsense can be defined by equation 2, just by taking the

gain error and input offset voltage as inaccuracy parameters:

Isense_full_scale*Rsense= Vcc−200mV

TSC_Gain1+Eg −2Vio

(2)

The Vsense parameter is defined in the electrical characteristics following equation 2.

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.

•

If power dissipation in the shunt is the key point, RSense should be chosen as follows:

Rsense≤PmaxImax²

and then choosing the right gain. For example, for high current to sense, the TSC2012H can offer a gain of

100, in this manner a smaller shunt can be used and so limited power losses. However accuracy can be

lower.

•

Or choosing the product available on the shelf, and then size the shunt resistor value accordingly.

5.5

Input offset voltage drift overtemperature

The maximum input offset voltage drift overtemperature 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 overtemperature enables the system designer to anticipate the effect of

temperature variations.

The maximum input voltage drift overtemperature is computed using equation 3:

ΔVioΔT=maxVioT −Vio25°C

T−25°C

(3)

where T = -40 °C and 150 °C.

The TSC2011H datasheet maximum value is guaranteed by measurements on a representative sample size

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

TSC2010H, TSC2011H, TSC2012H

Application information

DS13791 - Rev 2

page 28/49