OUT

V+

VIN+

VIN-

PCB pad

0.1 µF

VIA to Ground Plane

Supply Voltage

Output

PCB pad

To Bus

Voltage

To Load

RL

GND

RSHUNT

INA138

INA168

18

INA138, INA168

SBOS122E – DECEMBER 1999 – REVISED DECEMBER 2017

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Copyright © 1999–2017, Texas Instruments Incorporated

9 Power Supply Recommendations

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). A 0.1-µF capacitor is recommenced to be placed near the power supply pin on the INA138 or

INA168. Additional capacitance may be required for applications with noisy power supply voltages.

10 Layout

10.1 Layout Guidelines

Figure 19 shows the basic connection of the INA138 device. The input pins, VIN+ and VIN– , should be connected

as 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

voltage measured directly across RL. This is especially important in high-current systems where load current

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.

10.2 Layout Example

Figure 19. Typical Layout Example