INA138, INA168

6

SBOS122C

www.ti.com

FIGURE 1. Basic Circuit Connections.

Shunt

R

S

INA138

2

1

OUT

Q1

R

L

I

0

+

V

O

–

Load

R

G1

5k

Ω

R

G2

5k

Ω

V

IN+

V

IN–

3

4

I

S

V+

5

NOTE: (1) Maximum V

V+ power can be common or

independent of load supply.

2.7

V

P

Load Power Supply

VOLTAGE GAIN

1

5k

4.99k

2

10k

10k

5

25k

24.9k

10

50k

49.9k

20

100k

100k

50

250k

249k

100

500k

499k

Some Analog-to-Digital (A/D) converters have input imped-

ances that will significantly affect measurement gain. The input

impedance of the A/D converter can be included as part of the

Alternatively, an op amp can be used to buffer the A/D converter

OUTPUT VOLTAGE RANGE

The output of the INA138 is a current, which is converted to

accurate within the compliance voltage range of the output

circuitry. The shunt voltage and the input common-mode and

power-supply voltages limit the maximum possible output

swing. The maximum output voltage compliance is limited by

the lower of the two equations below:

or

(4)

(whichever is lower)

BANDWIDTH

Measurement bandwidth is affected by the value of the load

yield a narrower measurement bandwidth (see Typical

Characteristics). For widest possible bandwidth, keep the

capacitive load on the output to a minimum. Reduction in

bandwidth due to capacitive load is shown in the Typical

Characteristics.

If bandwidth limiting (filtering) is desired, a capacitor can be

added to the output (see Figure 3). This will not cause

instability.

APPLICATIONS

The INA138 is designed for current shunt measurement

circuits, as shown in Figure 1, but its basic function is useful

in a wide range of circuitry. A creative engineer will find many

unforeseen uses in measurement and level shifting circuits.

A few ideas are illustrated in Figures 2 through 7.