CAL =

0.00512

Current_LSB

R

SHUNT

·

Maximum Expected Current

2

15

Current_LSB =

INA226

SBOS547

– JUNE 2011

www.ti.com

PROGRAMMING THE INA226

An important aspect of the INA226 is that it does not necessarily measure current or power. The INA226

measures both the differential voltage applied between the VIN+ and VIN- input pins and the voltage applied to

the VBUS pin. In order for the INA226 to report both current and power values, the user must program the

resolution of the Current Register and the value of the shunt resistor present in the application to develop the

differential voltage applied between the input pins. The Power Register is internally set to be 25 times the

programmed Current_LSB. Both the Current_LSB and shunt resistor value are used in the calculation of the

Calibration Register value the INA226 uses to calculate the corresponding current and power values based on

the measured shunt and bus voltages.

The Calibration Register is calculated based on Equation 1. This equation includes the term Current_LSB. This is

the programmed value for the LSB for the Current Register. This is the value the user will use to convert the

value in the Current Register to the actual current in amps. The highest resolution for the Current Register can

be obtained by using the smallest allowable Current_LSB based on the maximum expected current as shown in

Equation 2. While this value will yield the highest resolution, it is common to select a value for the Current_LSB

to the nearest round number above this value to simplify the conversion of the Current Register and Power

Register to amps and watts respectively. The RSHUNT term is the value of the external shunt used to develop

the differential voltage across the input pins. The 0.00512 value in Equation 1 is an internal fixed value used to

ensure scaling is maintained properly.

(1)

(2)

Once the Calibration Register has been programmed, the Current Register and Power Register will be updated

accordingly based on the corresponding shunt voltage and bus voltage measurements. Until the Calibration

Register is programmed, the Current and Power Registers remain at zero.

14

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