INA219: Selecting Current Sense Resistor for IN219

joe lindula

Part Number: INA219

Hello, I have not used the INA219 or have done any current sensing in my past designs. I'm having a little trouble calculating the value of the Rshunt resistor. Let me run my numbers by anyone in the forum and see if I'm lost of on the right path.

Maximum Expected Load Current: 2.45A

Nominal load current = 1.225A

Full Scale voltage setting 40mV

Rshunt = Max Expected Load Current / Full Scale Voltage = 40mV/2.45A = 16.3mOhms

Vshunt = 1.225A*16.3mOhm = 20mV

Common mode voltage is 0.85V.

Voltage at IN- = (0.85 - 0.01996) = 0.83V

Resolution = 2.45A / 2^15 = 74uA/Bit

Does this sound reasonable or am I way off?

Thanks,

Joe

over 7 years ago

0 Patrick Simmons over 7 years ago

TI__Mastermind 26335 points

Hello Joe,

Thanks for your interest in our INA219. The majority of what you have looks correct. However, you will need to adjust the final resolution equation. The data sheet is a little misleading as the formula should be like below. Since you are using PGA=/1, you will divide by 2^12.

0 joe lindula over 7 years ago in reply to Patrick Simmons

Mastermind 6940 points

HI Patrick,

Thank you for responding to my post. I made an error in my message.

I should have said:

Rshunt = Full Scale Voltage / Max Expected Load Current = 40mV/2.45A = 16.3mOhms

Is that a correct way to calculate Rshunt value?

Thanks,
Joe

0 Patrick Simmons over 7 years ago in reply to joe lindula

TI__Mastermind 26335 points

Hello joe,

Yes that is what it should have been. I did not bother to correct you before as the number calculation portion was still correct.

Amplifiers

Amplifiers forum

INA219: Selecting Current Sense Resistor for IN219