INA216 datasheet(12/24 Pages) TI2

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Error_R

FILTER

? 100

)

FILTER

SHUNT

IN+

IN-

OUT

IN-

IN+

GND

SHUNT

FILTER

INA216

Load

FILTER

OUT

IN-

IN+

GND

SHUNT

INA216

Load

10W

PROTECT

10W

PROTECT

INA216

SBOS503C

– JUNE 2010 – REVISED NOVEMBER 2011

www.ti.com

Input Filtering

driving any current). Connecting a 100k

Ω load to the

4V output now increases the current by an additional

An ideal location where filtering is implemented is at

μA. This increase in current flowing through the

the inputs for a device. Placing an input filter in front

IN+ pin would change the additional gain error from

of the INA216, though, is not recommended but can

0.3% to 1.3%.

be implemented if it is determined to be necessary.

This

location

not

recommended

for

filtering

If filtering is required for the application and the gain

because adding input filters induces an additional

error introduced by the input filter resistors exceeds

gain error to the device that can easily exceed the

the available error budget for this circuit, a filter can

device maximum gain error specification of 0.2%. In

be implemented following the INA216. Placing a filter

the INA216, the nominal current into the IN+ pin is in

at the output of the current shunt monitor is not

the range of 13

μA while the bias current into the IN–

typically the ideal location because the benefit of the

pin is in the range of approximately 3

μA. The current

low impedance output of the amplifier is lost.

flowing into the IN+ pin includes both the input bias

Applications that require the low impedance output

current as well as the quiescent current. Where the

require an additional buffer amplifier that follows the

issue of input filtering begins to become more of an

post current shunt monitor filter.

issue is that as the quiescent current of the INA216

also flows through the IN+ pin, when the output

Using the INA216 With Transients Above 5.5V

begins to drive current, this additional current also

With a small amount of additional circuitry, INA216

flows through the IN+ pin, creating an even larger

can be used in circuits subject to transients higher

error.

than 5.5V. Use only zener diode or zener-type

Placing a typical common-mode filter of 10

Ω in series

transient absorbers, which are sometimes referred to

with each input and a 0.1

μF capacitor across the

as Transzorbs. Any other type of transient absorber

input pins, as shown in Figure 21, introduces an

has an unacceptable time delay. To use these

additional gain error into the system. For example,

protection devices, resistors are required in series

consider an application using the INA216A3 with a

with the INA216 inputs, as shown in Figure 22. These

full-scale output of 4V, assuming that the device is

resistors serve as a working impedance for the zener.

not driving any output current. The shunt voltage

It is desirable to keep these resistors as small as

needed to create the 4V output with a gain of 100 is

possible because of the error described in the Input

40mV. With 10

Ω filter resistors on each input, there is

Filtering section. These protection resistors are most

a difference voltage created that subtracts from the

often around 10

Ω. Larger values can be used with a

40mV full-scale differential current. The error can be

greater impact to the total gain error. Because this

calculated using Equation 2.

circuit

limits

only

short-term

transients,

many

applications are satisfied with a 10

Ω resistor along

with conventional zener diodes of the lowest power

(2)

rating that can be found. This combination uses the

least amount of board space. These diodes can be

found in packages as small as SOT-523 or SOD-523.

The use of these protection components may allow

the INA216 to survive from being damaged in

environments where large transients are common.

Figure 21. Input Filter

As mentioned previously, the current flowing into the

IN+ pin increases once the output begins to drive

current because of the quiescent current also flowing

Figure 22. Transient Protection Using Dual Zener

into the IN+ pin. The previous example resulted in an

Diodes

additional gain error of 0.3% as a result of the 10

filter resistors (assuming the output stage was not

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