Are the considerations for setCalibration_16V_400mA() correct?

[wollewald]

Hi, thanks for your library!

First a minor issue: In Adafruit_INA219.cpp, in function setCalibration_16V_400mA(), you say you are using the highest precision 0.1 mA.

Adafruit_INA219/Adafruit_INA219.cpp

Lines 391 to 395 in ce59837

	void Adafruit_INA219::setCalibration_16V_400mA() {
	// Calibration which uses the highest precision for
	// current measurement (0.1mA), at the expense of
	// only supporting 16V at 400mA max.

But according to line 416 the current LSB you are using is 0.00005:

Adafruit_INA219/Adafruit_INA219.cpp

Line 416 in ce59837

// CurrentLSB = 0.00005 (50uA per bit)

My main question is about the voltage limitation. In these lines you calculate the maximum power:

Adafruit_INA219/Adafruit_INA219.cpp

Lines 454 to 457 in ce59837

	// 8. Compute the Maximum Power
	// MaximumPower = Max_Current_Before_Overflow * VBUS_MAX
	// MaximumPower = 0.4 * 16V
	// MaximumPower = 6.4W

Why is 16 V the limit? Here, some calculations using 400 mA / 32 V:

• The LSB of the Bus Voltage Register is 4mV, so the Bus Voltage Register would be 8000 at 32 V.
• Using an 0.1 ohm shunt the value in the shunt voltage register would be 4000 at 400 mA (= 40 mV shunt voltage)
• The value in the Current Register would be : Shunt Voltage Register x Calibration Register / 4096 = 4000 * 8192 / 4096 = 8000.
• With these values, the Bus Power Register would be: Current Register * Bus Voltage Register / 5000 = 8000 * 8000 / 5000 = 12800, which is 12.8 W.

So, I can't see any overflow or other issue and therefore I would say there is no limitation to 16 V in this mode. Or have I forgotten anything?