9

®

INA122

any small positive voltage applied to V

IN

output must swing below 0V, which is clearly impossible

without a negative power supply.

To achieve common-mode range that extends to single-

supply ground, the INA122 uses precision level-shifting

buffers on its inputs. This shifts both inputs by approxi-

As a result of this input level-shifting, the voltages at pin 1

and pin 8 are not equal to their respective input terminal

voltages (pins 2 and 3). For most applications, this is not

important since only the gain-setting resistor connects to

these pins.

LOW VOLTAGE OPERATION

The INA122 can be operated on a single power supply as

low as +2.2V (or a total of +2.2V on dual supplies). Perfor-

mance remains excellent throughout the power supply range

up to +36V (or

±18V). Most parameters vary only slightly

throughout this supply voltage range—see typical perfor-

mance curves.

Operation at very low supply voltage requires careful atten-

tion to ensure that the common-mode voltage remains within

its linear range.

LOW QUIESCENT CURRENT OPERATION

The INA122 maintains its low quiescent current (60

µA)

while the output is within linear operation (up to 200mV

from the supply rails). When the input creates a condition

that overdrives the output into saturation, quiescent current

quiescent current increases to approximately 400

µA. Like-

supply ground) the quiescent current increases to approxi-

mately 200

µA.

OUTPUT CURRENT RANGE

Output sourcing and sinking current values versus the output

voltage ranges are shown in the typical performance curves.

The positive and negative current limits are not equal.

Positive output current sourcing will drive moderate to high

load impedances. Battery operation normally requires the

careful management of power consumption to keep load

impedances very high throughout the design.

FIGURE 6. Single-Supply Current Shunt Measurement.

INA122

ADS7816

12-Bit A/D

V

IN

R

G

R

S

0.02

Ω

I

L

2.5A

+

V

IN

–

3

2

4

5

6

7

G = 100

1

8

+5V

V+

Differential measurement

avoids ground loop errors.

Load

Shunt

7

5

6

8

4

2

1

3

Chip Select

Clock

Serial Data

CS

CLK

D

V

REF

+IN

–IN

1k

Ω

0.47µF

50mV

FIGURE 5. Micropower Single Supply Bridge Amplifier.

1k

Ω

REF200

200µA

INA122

3

8

7

4

5

6

2

1

V

≈ 200mV

V

IN

+

V

IN

R

G

V

V

O

–

(60µA)

+5V

NOTE: (1) To accomodate bipolar input signals,

V

voltage is then referred to the voltage applied to Ref.