LTC4260 Linear Technology, LTC4260 Datasheet - Page 17

• Manufacturer Part Number: LTC4260
• Description: Positive High Voltage Hot Swap Controller
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
Digital Interface
The LTC4260 communicates with a bus master using a
2-wire interface compatible with the I
SMBus, an I
The LTC4260 is a read-write slave device and supports
SMBus bus Read Byte, Write Byte, Read Word and Write
Word commands. The second word in a Read Word
command will be identical to the first word. The second
word in a Write Word command is ignored. The data
formats for these commands are shown in Figures 7 to10.
Using Optoisolators with SDA
The LTC4260 separates the SDA line into SDAI and SDAO.
If optoisolators are not used then tie SDAI and SDAO
together to construct a normal SDA line. When using
optoisolators connect the SDAI to the output of the incom-
ing opto and connect the SDAO to the input of the out-
going opto (see Figure 13).
START and STOP Conditions
When the bus is idle, both SCL and SDA must be high. A
bus master signals the beginning of a transmission with a
START condition by transitioning SDA from high to low
while SCL is high. When the master has finished commu-
nicating with the slave, it issues a STOP condition by
transitioning SDA from low to high while SCL is high. The
bus is then free for another transmission.
I
Twenty-seven distinct bus address are configurable using
the three-state ADR0-ADR2 pins. Table 1 shows the
correspondence between pin states and addresses. Note
that address bits B7 and B6 are internally configured to 10.
In addition, the LTC4260 will respond to two special
addresses. Address (1011 111)b is a mass write used to
write to all LTC4260, regardless of their individual address
settings. The mass write can be masked by setting register
bit A4 to zero. Address (0001 100)b is the SMBus Alert
Response Address. If the LTC4260 is pulling low on the
ALERT pin, it will acknowledge this address using the
SMBus Alert Response Protocol.
2
C Device Addressing
2
C extension for low power devices.
U
U
W
2
C bus and the
U
Acknowledge
The acknowledge signal is used for handshaking between
the transmitter and the receiver to indicate that the last
byte of data was received. The transmitter always releases
the SDA line during the acknowledge clock pulse. When
the slave is the receiver, it must pull down the SDA line so
that it remains LOW during this pulse to acknowledge
receipt of the data. If the slave fails to acknowledge by
leaving SDA HIGH, then the master can abort the transmis-
sion by generating a STOP condition. When the master is
receiving data from the slave, the master must pull down
the SDA line during the clock pulse to indicate receipt of
the data. After the last byte has been received the master
will leave the SDA line HIGH (not acknowledge) and issue
a STOP condition to terminate the transmission.
Write Protocol
The master begins communication with a START condi-
tion followed by the seven bit slave address and the R/W
bit set to zero. The addressed LTC4260 acknowledges this
and then the master sends a command byte which indi-
cates which internal register the master wishes to write.
The LTC4260 acknowledges this and then latches the
lower three bits of the command byte into its internal
Register Address pointer. The master then delivers the
data byte and the LTC4260 acknowledges once more and
latches the data into its internal register. The transmission
is ended when the master sends a STOP condition. If the
master continues sending a second data byte, as in a Write
Word command, the second data byte will be acknowl-
edged by the LTC4260 but ignored.
Read Protocol
The master begins a read operation with a START condi-
tion followed by the seven bit slave address and the R/W
bit set to zero. The addressed LTC4260 acknowledges this
and then the master sends a command byte that indicates
which internal register the master wishes to read. The
LTC4260 acknowledges this and then latches the lower
three bits of the command byte into its internal Register
Address pointer. The master then sends a repeated START
condition followed by the same seven bit address with the
LTC4260
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