INA169 Breakout Board Hookup Guide

Contributors: Shawn Hymel

Board Overview

Take a look at the schematic, and you will notice that the breakout board consists of a shunt resistor (R_S), the INA169 chip, and an output resistor (R_L). While R_S and R_L might appear to have 2 resistors, only one is populated on the board. If you would like to change the values of the resistors, you can replace them or put another resistor in parallel.

As current passes from V_IN+ through R_S to V_IN-, it creates a voltage drop across R_S. The op-amp inside of the INA169 chip measures the difference between the V_IN+ and V_IN- voltages and outputs a voltage based on that difference. The output of the op-amp is amplified through the internal transistor, which sources a current out of the INA169 chip. As that current passes through R_L to ground, a voltage level is generated at V_OUT.

Measuring Current

The voltage at V_OUT can be measured using an oscilloscope or an analog-to-digital converter. A bit of math is needed to convert to the source current (I_S):

I_S is the current we want to measure.

V_OUT is the voltage we measured at the output of the INA169.

1kΩ is a constant resistance value we need to include due to the internals of the INA169.

R_S is the value of the shunt resistor. If you do not modify the board, then this is set at 10Ω.

R_L is the value of the output resistor. If you do not modify the board, then this is set at 10kΩ.

Example

For example, let's say that you hook up the board and you measure 2.8V at V_OUT. Plugging this into our equation, we would get:

This shows that you have 0.028A (or 28mA) flowing through your line.

The Pinout

There are only 5 pins on the breakout board.

GND should be connected to ground of the circuit you are trying to measure

VIN+ needs to be connected to the positive side of the source (e.g. battery, output pin, etc.)

VIN- needs to be connected to the positive side of the load (e.g. VCC on Arduino, positive side of an LED, etc.)

VOUT is the measured output and should be connected to something that measures voltage levels, such as a multimeter, oscilloscope, or an Arduino ADC pin

VCC is the supply power to the INA169, which needs to be connected to 3.3V, 5V, etc. This can be anywhere from 0 to 75V. Note that the V_OUT range depends on the voltage supplied by VCC.

In addition to the pins on VIN+ and VIN-, the board also has two large pads around R_S, which are capable of taking alligator clips should you want to have a temporary hookup. Note that GND and VCC will still need to be connected for the board to function.

Modifying Functionality

The INA169 cannot sense any differences across R_S greater than 500mV, and the output error increases once the voltage across R_S dips below 35mV. If you include the voltage drop across the internal transistor, this means that the default setup of the breakout board is limited to measuring a current range of about 3.5mA to 35mA.

If you would like to change that range, R_S and R_L can be replaced with resistors of different values. R_S can be removed and replaced with another resistor fairly easily. R_L is a bit more difficult as it is a small, surface mount resistor. Changing either of the resistors changes the equation from above.

With R_L at 10kΩ, changing R_S gives us the following ranges: