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INA260, measuring own current
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INA260, measuring own current

by tomjennings on Thu Aug 27, 2020 10:27 pm

I assumed (...) that I could attach an INA260 to a Feather M4, and have that board measure it's own current consumption, but I'm getting odd results. I realize the power consumed by the INA260 via it's Vcc pin will be part of the total, but for my purposes any error will be unimportant. The LEARN example shows the setup measuring an external load, eg. the (in that example) Metro board is not the device under test, but a bag on the side. (The LEARN page also has an error; it says to connect the INA260's "VIN" pin to the board's 3.3V, but I know it means to connect the INA260's VCC pin to 3.3V).

I've got it wired to measure high side. The INA260 is connected and it's supply voltage reading matches my Fluke bench meter.

I have the INA260's +VIN connected to my LiPo battery (high side)
I have the INA260's -VIN connected to the BAT pin on the Feather (low side)

The board idles (with SDcard, an NRF24L01+ radio, and an audio amp that's shutdown 99% of the time) around -38 mA. The sign of that value is wrong, I believe.

What's definitely wrong is that the measured current drops to zero (!) when I PWM an attached LED (I'm guessing 20 mA).

Obviously something's wrong here. Does the INA260 require that it's VCC (3.3V) be completely isolated from the big VIN shunt? That would be a big disappointment.

tomjennings
 
Posts: 78
Joined: Thu Aug 17, 2006 1:21 am

Re: INA260, measuring own current

by tomjennings on Fri Aug 28, 2020 1:51 pm

My bad (as per usual). I overlooked the Feather on-board LiPo charger being fed from USB 5V was pushing power onto the BAT pin, on the M4 board. I've got a "shield" with separate solar charger/power mgt, LiPo andmy loads (audio player, big LED, etc).

I knew up front that the Feather's USB power couldn't be disabled but I thought I had isolated it. I hadn't. So it really was pushing power "backwards" through the shunt (charge, instead of discharge).

NEVER MIND.

tomjennings
 
Posts: 78
Joined: Thu Aug 17, 2006 1:21 am

Please be positive and constructive with your questions and comments.