Common Mode Voltage (V)

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0

0.006

0.012

0.018

0.024

0.03

0.036

0.042

0.048

0.054

0.06

D033

A1

A2

A3

A4

15

INA180, INA2180

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SBOS741A – APRIL 2017 – REVISED AUGUST 2017

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Feature Description (continued)

8.3.4 Rail-to-Rail Output Swing

The INAx180 allow linear current sensing operation with the output close to the supply rail and GND. The

maximum specified output swing to the positive rail is 30 mV, and the maximum specified output swing to GND is

only 5 mV. In order to compare the output swing of the INAx180 to an equivalent operational amplifier (op amp),

the inputs are overdriven to approximate the open-loop condition specified in op amp data sheets. The current-

sense amplifier is a closed-loop system; therefore, the output swing to GND can be limited by the product of the

offset voltage and amplifier gain.

For devices that have positive offset voltages, the swing to GND is limited by the larger of either the offset

voltage multiplied by the gain or the swing to GND specified in the Electrical Characteristics table.

For example, in an application where the INA180A4 (gain = 200 V/V) is used for low-side current sensing and the

device has an offset of 40 µV, the product of the device offset and gain results in a value of 8 mV, greater than

the specified negative swing value. Therefore, the swing to GND for this example is 8 mV. If the same device

has an offset of –40 µV, then the calculated zero differential signal is –8 mV. In this case, the offset helps

overdrive the swing in the negative direction, and swing performance is consistent with the value specified in the

Electrical Characteristics table.

The offset voltage is a function of the common-mode voltage as determined by the CMRR specification;

therefore, the offset voltage increases when higher common-mode voltages are present. The increase in offset

voltage limits how low the output voltage can go during a zero-current condition when operating at higher

common-mode voltages. The typical limitation of the zero-current output voltage vs common-mode voltage for

each gain option is shown in Figure 37.

Figure 37. Zero-Current Output Voltage vs Common-Mode Voltage

8.4 Device Functional Modes

8.4.1 Normal Mode

The INAx180 is in normal operation when the following conditions are met:

•

•

•

•

The minimum differential input signal times gain is greater than the swing to GND (see the Rail-to-Rail Output

Swing section).

During normal operation, the device produces an output voltage that is the gained-up representation of the

difference voltage from IN+ to IN–.