INA169 Breakout Board Hookup Guide

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Contributors: Shawn Hymel
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Board Overview

Take a look at the schematic, and you will notice that the breakout board consists of a shunt resistor (RS), the INA169 chip, and an output resistor (RL). While RS and RL 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.

INA169 Breakout Schematic

INA169 Current Sensing Breakout Schematic

As current passes from VIN+ through RS to VIN-, it creates a voltage drop across RS. The op-amp inside of the INA169 chip measures the difference between the VIN+ and VIN- 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 RL to ground, a voltage level is generated at VOUT.

IMPORTANT: The INA169 is configured to measure DC only. The VIN+ pin must be at a higher potential than the VIN- pin, which means that the INA169 cannot measure AC.

Measuring Current

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

alt text

IS is the current we want to measure.

VOUT 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.

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

RL 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 VOUT. Plugging this into our equation, we would get:

alt text

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

The Pinout

There are only 5 pins on the breakout board.

Pinout of INA169 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 VOUT 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 RS, 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 RS greater than 500mV, and the output error increases once the voltage across RS 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, RS and RL can be replaced with resistors of different values. RS can be removed and replaced with another resistor fairly easily. RL is a bit more difficult as it is a small, surface mount resistor. Changing either of the resistors changes the equation from above.

With RL at 10kΩ, changing RS gives us the following ranges:


RS Current Sense Range
10Ω 3.5mA - 35mA
35mA - 350mA
0.1Ω 350mA - 3.5A


IMPORTANT: Be careful with the power rating on the resistor! If you choose a 0.1Ω resistor for RS and expect to see 3.5A through it, this can result in 1.2W of heat being generated - way too much for your average ¼W resistor! You will need a resistor that can handle at least 2W. The following power resistors are recommended:

  • Ohmite 1Ω 1% 3W
  • Ohmite 0.1Ω 1% 3W