INA191 datasheet(17/41 Pages) TI

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7.4 Device Functional Modes

7.4.1 Normal Operation

The INAx191 is in normal operation when the following conditions are met:

• The power-supply voltage (VS) is between 1.7 V and 5.5 V.

• The common-mode voltage (VCM) is within the specified range of –0.2 V to +40 V.

• The maximum differential input signal times the gain plus VREF is less than the positive output voltage swing

VSP. VREF = 0 V for INA191.

• The ENABLE pin is driven or connected to VS.

• The minimum differential input signal times the gain plus VREF is greater than the swing to GND, VZL (see

Section 7.3.7). VREF = 0 V for INA191.

During normal operation, this device produces an output voltage that is the amplified representation of the

difference voltage from IN+ to IN– plus the voltage applied to the REF pin. For devices without a REF pin the

REF voltage is 0 V.

7.4.2 Unidirectional Mode

The INA191 always monitors current flow in a single direction, however, the INA2191 can be configured to

monitor current flowing in one direction (unidirectional) or in both directions (bidirectional) depending on how the

REF pin is connected. The most common case is unidirectional where the output is set to ground when no

current is flowing by connecting the REF pin to ground, as shown in Figure 7-4. When the current flows from the

bus supply to the load, the input voltage from IN+ to IN– increases and causes the output voltage at the OUT pin

to increase. Pin names such as OUT apply to either OUT1 or OUT2 in the diagrams below depending on which

channel is used.

VOUT

1.7 V to 5.5 V

IN±

IN+

OUT

Bus Voltage

up to 40 V

RSENSE

Load

Capacitively

Coupled

Amplifier

ENABLE

INA2191 (½)

REF

GND

ISENSE

CBYPASS

0.1 µF

Figure 7-4. Typical Unidirectional Application

The linear range of the output stage is limited by how close the output voltage can approach ground under zero

input conditions. The zero current output voltage of the INA2191 is very small and for most unidirectional

applications the REF pin is simply grounded. However, if the measured current multiplied by the current sense

resistor and device gain is less than the zero current output voltage then bias the REF pin to a convenient value

above the zero current output voltage to get the output into the linear range of the device. To limit common-mode

rejection errors, buffer the reference voltage connected to the REF pin.

A less-frequently used output biasing method is to connect the REF pin to the power-supply voltage, VS. This

method results in the output voltage saturating at 40 mV less than the supply voltage when no differential input

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INA191, INA2191

SLYS020B – FEBRUARY 2019 – REVISED FEBRUARY 2021

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