ina219 datasheet

Corrected_Full_Scale_Cal = trunc
Cal MeasShuntCurrent
INA219_Current
´
INA219
www.ti.com SBOS448G –AUGUST 2008–REVISED DECEMBER 2015
Programming (continued)
8.5.2 Programming the Power Measurement Engine
8.5.2.1 Calibration Register and Scaling
The Calibration Register enables the user to scale the Current Register (04h) and Power Register (03h) to the
most useful value for a given application. For example, set the Calibration Register such that the largest possible
number is generated in the Current Register (04h) or Power Register (03h) at the expected full-scale point. This
approach yields the highest resolution using the previously calculated minimum Current_LSB in the equation for
the Calibration Register. The Calibration Register can also be selected to provide values in the Current Register
(04h) and Power Register (03h) that either provide direct decimal equivalents of the values being measured, or
yield a round LSB value for each corresponding register. After these choices have been made, the Calibration
Register also offers possibilities for end user system-level calibration. 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 INA219 to cancel the total system error as shown in Equation 6.
(6)
8.5.3 Simple Current Shunt Monitor Usage (No Programming Necessary)
The INA219 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 Default Settings
The default power-up states of the registers are shown in the Register Details section of this data sheet. These
registers are volatile, and if programmed to other than default values, must be re-programmed at every device
power-up. Detailed information on programming the Calibration register specifically is given in the section,
Programming the Calibration Register.
8.5.5 Bus Overview
The INA219 offers compatibility with both I
2
C and SMBus interfaces. The I
2
C and SMBus protocols are
essentially compatible with one another.
The I
2
C interface is used throughout this data sheet as the primary example, with SMBus protocol specified only
when a difference between the two systems is being addressed. Two bidirectional lines, SCL and SDA, connect
the INA219 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.
To address a specific device, the master initiates a START condition by pulling the data signal line (SDA) from a
HIGH to a LOW logic level while SCL is HIGH. All slaves on the bus shift in the slave address byte on the rising
edge of SCL, with the last bit indicating whether a read or write operation is intended. During the ninth clock
pulse, the slave being addressed responds to the master by generating an Acknowledge and pulling SDA LOW.
Data transfer is then initiated and eight bits of data are sent, followed by an Acknowledge bit. During data
transfer, SDA must remain stable while SCL is HIGH. Any change in SDA while SCL is HIGH is interpreted as a
START or STOP condition.
Once all data have been transferred, the master generates a STOP condition, indicated by pulling SDA from
LOW to HIGH while SCL is HIGH. The INA219 includes a 28-ms timeout on its interface to prevent locking up an
SMBus.
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