Corrected_Full_Scale_Cal = trunc

Cal

MeasShuntCurrent

´

INA220_Current

Current Re gister Bus Voltage Re gister

Power Register

5000

´

=

Shunt Voltage Re gister Calibration Re gister

Current Register

4096

´

=

12

INA220

SBOS459E – JUNE 2009 – REVISED JANUARY 2016

www.ti.com

Product Folder Links: INA220

Submit Documentation Feedback

Copyright © 2009–2016, Texas Instruments Incorporated

Programming (continued)

Shunt voltage is calculated by multiplying the Shunt Voltage Register contents with the Shunt Voltage LSB of 10

μV. The Bus Voltage register bits are not right-aligned. To compute the value of the Bus Voltage, Bus Voltage

Register contents must be shifted right by three bits. This shift puts the BD0 bit in the LSB position so that the

contents can be multiplied by the Bus Voltage LSB of 4-mV to compute the bus voltage measured by the device.

After programming the Calibration Register, the value expected in the Current Register (04h) can be calculated

by multiplying the Shunt Voltage register contents by the Calibration Register and then dividing by 4096 as

shown in Equation 4. To obtain a value in amperes, the Current register value is multiplied by the programmed

Current_LSB.

(4)

The value expected in the Power register (03h) can be calculated by multiplying the Current register value by the

Bus Voltage register value and then dividing by 5000 as shown in Equation 5. Power Register content is

multiplied by Power LSB which is 20 times the Current_LSB for a power value in watts.

(5)

8.5.2 Programming the INA220 Power Measurement Engine

8.5.2.1 Calibration Register and Scaling

The Calibration register makes it possible to set the scaling of the Current and Power registers to whatever

values are most useful for a given application. One strategy may be to set the Calibration register such that the

largest possible number is generated in the Current register or Power register at the expected full-scale point;

this approach yields the highest resolution. The Calibration register can also be selected to provide values in the

Current and Power registers that either provide direct decimal equivalents of the values being measured, or yield

a round LSB number. After these choices have been made, the Calibration register also offers possibilities for

end-user system-level calibration, where the value is adjusted slightly to cancel total system error. After

determining the exact current by using an external ammeter, the value of the Calibration Register can then be

adjusted based on the measured current result of the INA220 to cancel the total system error as shown in

Equation 6.

(6)

8.5.3 Simple Current Shunt Monitor Usage (No Programming Necessary)

The INA220 can be used without any programming if it is only necessary to read a shunt voltage drop and bus

voltage with the default 12-bit resolution, 320-mV shunt full-scale range (PGA = /8), 32-V bus full-scale range,

and continuous conversion of shunt and bus voltage.

Without programming, current is measured by reading the shunt voltage. The Current register and Power register

are only available if the Calibration register contains a programmed value.

8.5.4 Bus Overview

essentially compatible with one another.

when a difference between the two systems is being addressed. Two lines, SCL and SDA, connect the INA220

to the bus. Both SCL and SDA are open-drain connections.

The device that initiates the transfer is called a master, and the devices controlled by the master are slaves. The

bus must be controlled by a master device that generates the serial clock (SCL), controls the bus access, and

generates START and STOP conditions.