Equation 10 has been described for a temperature of 25 °C. With any temperature variation, ΔVio/dT error term

must be added. Furthermore, if the power supply is susceptible to change, the SVR parameter must also be

considered.

•

Example

The example below allows for a better understanding of the maximum total error that can happen on the output of

the TSC200.

•

Use case:

–

Vcc = 5 V

–

Vicm = 48 V

–

Temperature = 25 °C

–

Iload = 5 A

–

Shunt 20 mΩ with 1% accuracy

Theoretically, the expected output voltage should be Vout = Rshunt * Iload * 20 = 2 V.

From the above equations, all the error terms by using the maximum value of the electrical characteristic (when

available) are detailed in order to express as much as possible, the worst-case condition. The % error on output

of the following table is expressed in reference to Vout.

Table 6. Error on output

Error source

Calculus

Output voltage error

% error on

output

Gain error

20*20.10−3*5*1%

20 mV

1%

Vio error

20*2.5mV

50 mV

2.5%

CMRR error

20*48V−12V

1010020

7.2 mV

0.4%

Noise

20*55nVHz 30kHz*ln30k −ln0.1 +1MHz*π2−0.1Hz

1.5 mVRMS

0.2% (1)

Total

77.2 mV

+1.4 mVRMS

4.1%

1. The percentage is based on voltage peak value (3 times RMS value).

So, the maximum output voltage in the worst case condition at ambient temperature is 2.077 V + 1.5 mVRMS

instead of the expected 2 V. This represents an error in the current reading of about 4.1%. 1% more must be

added due to the shunt accuracy.

It is important to note that this calculus has been done by using all the maximum values and all the error terms

have been added to each other, meaning that the chance to get 4.1% precision in the above use case is

extremely low, even on the whole population the actual error is to a great extent smaller.

5.6

Root sum square approximation

A more realistic calculus is to use a statistical approach. Total error can be determined by using the root-sum-of-

the-squares (RSS), a simplified statistical method to combine the error terms. With this approach, the average

values considered are zero, and the maximum parameter values given in the datasheet have all the same Cpk

(the maximum is given for all values with the same number of sigma) max. = K * sigma.

So, the error can be written as equation 11.

Error= ∑k.sigma2= ∑maxdatasℎeet²

(11)

All these parameters must be summed up as described by equation 11.

Error_Rss= εG2+εsℎunt2+ Vio

Rsℎunt.Isense 2

+ Vicm−12V

CMRR

Rsℎunt.Isense 2

(12)

TSC200, TSC201, TSC202

Root sum square approximation

DS13882 - Rev 2

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