Datasheet

INA220
SBOS459D –JUNE 2009–REVISED SEPTEMBER 2010 www.ti.com
Serial Interface
When reading from the INA220, the last value stored
in the register pointer by a write operation determines
The INA220 operates only as a slave device on the
which register is read during a read operation. To
Two-Wire bus and SMBus. Connections to the bus
change the register pointer for a read operation, a
are made via the open-drain I/O lines SDA and SCL.
new value must be written to the register pointer. This
The SDA and SCL pins feature integrated spike
write is accomplished by issuing a slave address byte
suppression filters and Schmitt triggers to minimize
with the R/W bit LOW, followed by the register pointer
the effects of input spikes and bus noise. The INA220
byte. No additional data are required. The master
supports the transmission protocol for fast (1kHz to
then generates a START condition and sends the
400kHz) and high-speed (1kHz to 3.4MHz) modes.
slave address byte with the R/W bit HIGH to initiate
All data bytes are transmitted most significant byte
the read command. The next byte is transmitted by
first.
the slave and is the most significant byte of the
register indicated by the register pointer. This byte is
WRITING TO/READING FROM THE INA220
followed by an Acknowledge from the master; then
the slave transmits the least significant byte. The
Accessing a particular register on the INA220 is
master acknowledges receipt of the data byte. The
accomplished by writing the appropriate value to the
master may terminate data transfer by generating a
register pointer. Refer to Table 3 for a complete list of
Not-Acknowledge after receiving any data byte, or
registers and corresponding addresses. The value for
generating a START or STOP condition. If repeated
the register pointer as shown in Figure 17 is the first
reads from the same register are desired, it is not
byte transferred after the slave address byte with the
necessary to continually send the register pointer
R/W bit LOW. Every write operation to the INA220
bytes; the INA220 retains the register pointer value
requires a value for the register pointer.
until it is changed by the next write operation.
Writing to a register begins with the first byte
Figure 14 and Figure 15 show read and write
transmitted by the master. This byte is the slave
operation timing diagrams, respectively. Note that
address, with the R/W bit LOW. The INA220 then
register bytes are sent most-significant byte first,
acknowledges receipt of a valid address. The next
followed by the least significant byte. Figure 16
byte transmitted by the master is the address of the
shows the timing diagram for the SMBus Alert
register to which data will be written. This register
response operation. Figure 17 illustrates a typical
address value updates the register pointer to the
register pointer configuration.
desired register. The next two bytes are written to the
register addressed by the register pointer. The
INA220 acknowledges receipt of each data byte. The
master may terminate data transfer by generating a
START or STOP condition.
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