INA138-Q1, IN168-Q1

SGLS174D – SEPTEMBER 2003 – REVISED DECEMBER 2010

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APPLICATION INFORMATION

current measurement amplifier in this application is:

The maximum differential input voltage for accurate measurements is 0.5 V, which produces a 10 mA output

current. A differential input voltage of up to 2 V 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-negative voltage is applied to pin 3, the

BASIC CONNECTION

closely as possible to the shunt resistor to minimize any resistance in series with the shunt resistance. The

output resistor, RL, is shown connected between pin 1 and ground. Best accuracy is achieved with the output

could flow in the ground connections, affecting the measurement accuracy.

No power-supply bypass capacitors are required for stability of the INA138. However, applications with noisy or

high-impedance power supplies may require decoupling capacitors to reject power-supply noise. Connect bypass

capacitors close to the device pins.

POWER SUPPLIES

The input circuitry of the INA138 can accurately measure beyond its power-supply voltage, V+. For example, the

V+ power supply can be 5 V, whereas the load power supply voltage is up to +36 V (or +60 V with the INA168).

The output voltage range of the OUT terminal, however, is limited by the lesser of the two voltages (see Output

Voltage Range section).

better accuracy at lower currents by minimizing the effects of offset, while low values of RS minimize voltage loss

full-scale shunt voltage range of 50 mV to 100 mV. Maximum input voltage for accurate measurements is 500

mV.

Some analog-to-digital (A/D) converters have input impedances that significantly affects measurement gain. The

resistor to ground. Alternatively, an op amp can be used to buffer the A/D converter input. Figure 9 shows the

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