ltc4261cgn-trpbf Linear Technology Corporation, ltc4261cgn-trpbf Datasheet - Page 23

• Manufacturer Part Number: ltc4261cgn-trpbf
• Description: Negative Voltage Hot Swap Controllers With Adc And I2c Monitoring
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
I
The LTC4261/LTC4261-2 feature an I
vide access to the ADC data registers and four other reg-
isters for monitoring and control of the pass FET. Figure 9
shows a general data transfer format using the I
LTC4261/LTC4261-2 are read-write slave devices and
support 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 fi rst word. The second
word in a Write Word command is ignored. The data for-
mats for these commands are shown in Figures 10 to 13.
Using Optoisolators with SDA
The LTC4261/LTC4261-2 split the SDA line into SDAI (in-
put) and SDAO (output) for convenience of opto-coupling
with the host. If optoisolators are not used then tie SDAI
and SDAO together to form a normal SDA line. When us-
ing optoisolators, connect the SDAI to the output of the
incoming optoisolator and connect the SDAO to the input
of the outgoing optoisolator (see Figure 2). If the ALERT
2
C Interface
Figure 10. LTC4261 Serial Bus SDA Write Byte Protocol
S
FROM MASTER TO SLAVE
FROM SLAVE TO MASTER
SDA
SCL
0 0 1 a3:a0
ADDRESS
CONDITION
START
W
0
S
A
0
X X X X b3:b0
COMMAND
ADDRESS
a6 - a0
1 - 7
S
A: ACKNOWLEDGE (LOW)
A: NOT ACKNOWLEDGE (HIGH)
R: READ BIT (HIGH)
W: WRITE BIT (LOW)
S: START CONDITION
P: STOP CONDITION
0 0 1 a3:a0
ADDRESS
A
0
Figure 13. LTC4261 Serial Bus SDA Read Word Protocol
b7:b0
DATA
R/W
2
8
C interface to pro-
W
42612 F10
0
Figure 9. Data Transfer over I
A P
0
A
0
ACK
9
X X X X b3:b0
COMMAND
2
C. The
1 - 7
b7 - b0
DATA
A
0
S
line is used as an interrupt for the host to respond to a
fault in real time, connect the ALERT to an optoisolator in
a way similar to that for the SDAO as shown in Figure 2.
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 transiting SDA from high to low
while SCL is high. When the master has fi nished com-
municating with the slave, it issues a STOP condition by
transiting SDA from low to high while SCL is high. The
bus is then free for another transmission.
Stuck-Bus Reset
The LTC4261/LTC4261-2 I
bus reset timer. The low conditions of the SCL and the
SDAI pins are ORed to start the timer. The timer is reset
when both SCL and SDAI are pulled high. If the SCL pin
or the SDAI pin is held low for over 66ms, the stuck-bus
timer will expire and the internal I
0 0 1 a3:a0 1 0
ADDRESS
8
S
S
Figure 11. LTC4261 Serial Bus SDA Write Word Protocol
Figure 12. LTC4261 Serial Bus SDA Read Byte Protocol
0 0 1 a3:a0
0 0 1 a3:a0
2
ADDRESS
ADDRESS
C or SMBus
ACK
R A
9
DATA
b7:b0
W
W
0
0
A
0
A
0
LTC4261/LTC4261-2
1 - 7
A
0
X X X X b3:b0
X X X X b3:b0
COMMAND
COMMAND
DATA
b7:b0
b7 - b0
DATA
42612 F13
A P
1
2
8
C interface features a stuck-
A
A
0
0
S
b7:b0
DATA
2
ACK
C state machine will be
0 0 1 a3:a0 1 0
ADDRESS
9
A
0
X X X X X X X X
CONDITION
R A
STOP
DATA
42612 F09
P
DATA
b7:b0 1
23
42612 F11
42612 F12
A P
0
A P
42612fb