INA180: Setup advice.

Dharmesh,

1. A simulation load of 20 ohms will kind of work, but you must be careful to understand that as you change the voltage from 0V to 5V to create varied load currents, you will also be changing the common mode of the device.  This will affect the error performance of the part.  In terms of offset, it could likely be in your favor as with a common mode of 0V, the offset will be under 150uV guaranteed, but at larger values, it could be up to 500uV.

Another thing to note is the swing to ground spec.  If you are trying to measure currents down near 0mA, there will be some point where the amplifier goes non-linear.  For the INA180, this is around 5mV.

For shunt resistors,  A 1 ohm shunt resistor with 240mA through it creates 240mV of input voltage, and using the A1 version of the device, is x20, so that would produce 4.8V on the output of the shunt resistor.  So overall, that would be about the largest value I would expect, but lower values offer lower power consumption and smaller voltage drop.  If you have this device in a high side configuration, know that the bus rail at full 240mA is no longer 5V but 4.76V.  Current consumption through the shunt is just I=V/R.  For reference, the output of the current sense amp is Ishunt * Rshunt * Gain.  So, if you had a 20mOhm shunt, a gain of 200 (A4 device), and your current of 240mA, then you would get .24 * .020 * 200 = 0.96V on the output.  The output must be lower than the Vs supply of the device, and just a little lower than that to account for swing-to-supply-rail specs.

The error as you get lower and lower in current will increase.  There is a sidebar widget in the product page that can help you see what the error curve for your application will look like.  I put in a few values and here are the results.

To better understand implementations, the data sheet specs and all the sources of error in current sense amplifiers, there is a training video series we made that can help.

2. Depending on how you implement the current sense amp in the circuit, there are things to consider.  The INA180 may not be the best choice for a solenoid application if it's not a low-side or high-side only implementation.  For that, I would strongly recommend you look at the INA240, which excels in PWM and in-line solenoid and motor control applications.  Also, we produce tech notes that are like very short, 2 page app notes that can help you understand implementations and get product recommendations.  There are 5 tech notes already on solenoid and motor control.  Please take a look and see if they match your desired implementation.

Dharmesh,

regarding 1 - yes, you should size you shunt appropriately so that the maximum current * rshunt * gain < adc max input voltage.

Also remember to account for a little headroom - if you power the INA180 with 3.3 and expect 3.3V output, it won't reach 3.3 because of the amplifier headroom needed.  See this article for more on that.  However, if you only need to measure 1A and scale for 1.5A, then you're probably just fine.

for your other application, I'm assuming you meant 5V 0.240A and not 5V 0.240mA.  With a 660mΩ shunt and a gain = 20, then that would produce 3.168V at 240mA, which is reasonable.

The schematic looks ok to me, and the only thing I usually recommend is adding a spot for a low-pass pi filter to the front end.  You can always not populate the cap and install 0 ohm resistors if you don't need it, but it's great to have if you do, and it's good for debug as well.

It looks something like this:

Next, about pin configurations, they are labeled A and B - see below:

You can tell them apart in the ordering table at the end of the data sheet because it says INA180A1 or INA180B1 and so on.  The package markings are on the ordering table as well, so you can see which one you have if all you have is the physical part in your hand.

You can power the device from a GPIO switch, but make sure to have a bypass cap on it for the power supply still.

Another thing to think about is that you are driving an ADC, which means you're going to be pulling some current from the INA180 output drive circuitry, which is pretty weak.  Adding an RC filter to the output, and possibly even a buffer IC, is something to consider.  There is a parameter called "closed loop output impedance" which you can use to determine if a filter will be stable.  See this article and this app note for more. 

One final note - there is a lux light sensor that TI makes (OPT3001) and it measures darkness up to bright sunlight with good IR rejection and has an i2c interface.  Not sure if that helps, but I thought I would throw it out there.