INA139, INA169

6

SBOS181C

www.ti.com

FIGURE 2. Buffering Output to Drive the A/D Converter.

FIGURE 3. Output Filter.

I

S

OPA340

INA139

3

4

Z

IN

R

L

Buffer of amp drives the A/D converter

without affecting gain.

INA139

f

1

2

πR

V

O

f

–3dB

R

L

C

L

3

4

The maximum differential input voltage for accurate mea-

surements is 0.5V, which produces a 500

µA output current.

A differential input voltage of up to 2V will not cause damage.

Differential measurements (pins 3 and 4) must be unipolar

with a more-positive voltage applied to pin 3. If a more-

zero, but will not cause damage.

BASIC CONNECTION

Figure 1 shows the basic connection of the INA139. The

possible to the shunt resistor to minimize any resistance in

shown connected between pin 1 and ground. Best accuracy

is achieved with the output voltage measured directly across

where load current can flow in the ground connections,

affecting the measurement accuracy.

No power-supply bypass capacitors are required for stability

of the INA139. However, applications with noisy or high-

impedance power supplies can require decoupling capaci-

tors to reject power-supply noise; connect the bypass capaci-

tors close to the device pins.

POWER SUPPLIES

The input circuitry of the INA139 can accurately measure

beyond its power-supply voltage, V+. For example, the V+

power supply can be 5V whereas the load power-supply

voltage is up to +36V (or +60V with the INA169). However,

the output voltage range of the OUT terminal (pin 1) is limited

by the lesser of the two voltages (see the Output Voltage

Range section).

application and is a compromise between small-signal accu-

racy and maximum permissible voltage loss in the measure-

currents by minimizing the effects of offset, whereas low

that provides a full-scale shunt voltage of 50mV to 100mV;

maximum input voltage for accurate measurements is 500mV.

The output impedance of the INA139 OUT terminal is very

excellent accuracy. The input impedance of any additional

circuitry at the output must be much higher than the value of

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 input, as shown in Figure 2, see Figure 1 for

OUTPUT VOLTAGE RANGE

The output of the INA139 is a current that is converted to a

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:

(4)

or

(5)

(whichever is lower)

BANDWIDTH

Measurement bandwidth is affected by the value of the load

yield a narrower measurement bandwidth (see the Typical

Characteristics). For widest possible bandwidth, keep the

capacitive load on the output to a minimum.

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

added to the output, as shown in Figure 3, which will not

cause instability.

APPLICATIONS

The INA139 is designed for current shunt measurement

circuits (see 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 4 through 7.