ina219 datasheet

Current Register Bus Voltage Re gister
Power Register
5000
´
=
Shunt Voltage Re gister Calibration Re gister
Current Register
4096
´
=
Power_LSB = 20 Current_LSB
Maximum Expected Current
2
15
Current_LSB =
Cal = trunc
0.04096
Current_LSB R´
SHUNT
INA219
SBOS448G –AUGUST 2008–REVISED DECEMBER 2015 www.ti.com
8.5 Programming
An important aspect of the INA219 device is that it measure current or power if it is programmed based on the
system. The device measures both the differential voltage applied between the IN+ and IN- input pins and the
voltage at IN- pin. In order for the device to report both current and power values, the user must program the
resolution of the Current Register (04h) and the value of the shunt resistor (R
SHUNT
) present in the application to
develop the differential voltage applied between the input pins. Both the Current_LSB and shunt resistor value
are used in the calculation of the Calibration Register value that the device uses to calculate the corresponding
current and power values based on the measured shunt and bus voltages.
After programming the Calibration Register, the Current Register (04h) and Power Register (03h) update
accordingly based on the corresponding shunt voltage and bus voltage measurements. Until the Calibration
Register is programmed, the Current Register (04h) and Power Register (03h) remain at zero.
8.5.1 Programming the Calibration Register
The Calibration Register is calculated based on Equation 1. This equation includes the term Current_LSB, which
is the programmed value for the LSB for the Current Register (04h). The user uses this value to convert the
value in the Current Register (04h) to the actual current in amperes. The highest resolution for the Current
Register (04h) can be obtained by using the smallest allowable Current_LSB based on the maximum expected
current as shown in Equation 2. While this value yields 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
(04h) and Power Register (03h) to amperes and watts respectively. The R
SHUNT
term is the value of the external
shunt used to develop the differential voltage across the input pins. The Power Register (03h) is internally set to
be 20 times the programmed Current_LSB see Equation 3.
where
• 0.04096 is an internal fixed value used to ensure scaling is maintained properly (1)
(2)
(3)
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. In order 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)
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