INA216 datasheet(10/19 Pages) TI

10 / 19 page

Error_V

100

SENSE

INA216

SBOS503B – JUNE 2010 – REVISED JUNE 2010

www.ti.com

These comments have framed the decision on what

Calculating Total Error

the shunt resistor value should be, based on the

The electrical specifications for the INA216 include

full-scale

value;

but

many

applications

require

the typical individual errors terms such as gain error,

accurate measurements at levels as low as 10% of

offset

error,

and

nonlinearity

error.

Total

error

the full-scale value. At this level, the input offset

including all of these individual error components is

voltage of the current shunt monitor becomes a larger

not specified in the Electrical Characteristics table. To

percentage of the shunt voltage, and thus contributes

accurately calculate the error that can be expected

a larger error to the output. The percentage of error

from the device, we must first know the operating

created by the input offset voltage relative to the

conditions to which the device is subjected. Some

shunt voltage is shown in Equation 1.

current shunt monitors specify a total error in the

product data sheet. However, this total error term is

accurate under only one particular set of operating

(1)

conditions. Specifying the total error at this one point

Ideally, the differential input voltage at 10% would be

has little practical value, though, because any

increased to minimize the effects of the input offset

deviation from these specific operating conditions no

voltage; however, we are bound by the full-scale

longer yields the same total error value. This section

value. The full-scale output voltage on the INA216 is

discusses

the

individual

error

sources,

with

limited to 200mV below the supply voltage (IN+).

information on how to apply them in order to calculate

Selecting a shunt resistor to increase the shunt

the total error value for the device under normal

voltage at the low operating range of the load current

operating conditions.

could easily saturate the output of the current shunt

The typical error sources that have the largest impact

monitor at the full-scale load current. For applications

on the total error of the device are input offset

where accuracy over a larger range is needed, a

voltage, common-mode voltage rejection, gain error,

lower gain option (and therefore, a larger differential

and nonlinearity error.

input voltage) is selected. For applications where a

minimal voltage drop on the line that powers the load

The nonlinearity error of the INA216 is relatively low

is required, a higher gain option (and so, a smaller

compared to the gain error specification, which

differential input voltage) is selected.

results in a gain error that can be expected to be

relatively constant throughout the linear input range of

For example, consider a design that requires a

the device. While the gain error remains constant

full-scale output voltage of 4V, a maximum load

across the linear input range of the device, the error

current of 10A, and a maximum voltage drop on the

associated with the input offset voltage does not. As

common-mode line of 25mV. The 25mV maximum

the differential input voltage developed across a

voltage drop requirement and a 4V full-scale output

shunt resistor at the input of the INA216 decreases,

limits the gain option to the 200V/V device. A 100V/V

the inherent input offset voltage of the device

setting would require a maximum voltage drop of

becomes a larger percentage of the measured input

40mV with the other two lower gain versions creating

signal, resulting in an increase in measurement error.

larger voltage drops. Based on the gain of 200 on a

This varying error is present among all current shunt

4V full-scale output, the maximum differential input

monitors, given the input offset voltage ratio to the

voltage would be 20mV. The shunt resistor needed to

voltage being sensed by the device. The low input

create a 20mV drop with a 10A load current is 2m

Ω.

offset voltages present in the INA216 devices,

When choosing the proper shunt resistor, it is also

however, limit the amount of contribution the offset

important to consider that at higher currents, the

voltage has on the total error term.

power dissipation in the shunt resistor becomes

Two examples are provided that detail how different

greater. Therefore, it is important to evaluate the drift

operating

conditions

can

affect

the

total

error

of the sense resistor as a result of power dissipation,

calculations. Typical and maximum calculations are

and choose an appropriate resistor based on its

shown as well to provide the user more information

power wattage rating.

on how much error variance could be present from

device to device.

Submit Documentation Feedback

Product Folder Link(s): INA216

INA216 Datasheet(PDF) 10 Page - Texas Instruments

INA216 Datasheet(HTML) 10 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Datasheet Download

Link URL