LTC4261IGN datasheet(23/32 Pages) LINER

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LTC4261/LTC4261-2

42612fb

I2C Interface

The LTC4261/LTC4261-2 feature an I2C interface to pro-

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 I2C. The

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 ﬁrst 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

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 ﬁnished 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 I2C interface features a stuck-

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 I2C state machine will be

Figure 9. Data Transfer over I2C or SMBus

Figure 10. LTC4261 Serial Bus SDA Write Byte Protocol

Figure 11. LTC4261 Serial Bus SDA Write Word Protocol

Figure 12. LTC4261 Serial Bus SDA Read Byte Protocol

Figure 13. LTC4261 Serial Bus SDA Read Word Protocol

SCL

SDA

START

CONDITION

STOP

CONDITION

ADDRESS

R/W

ACK

DATA

ACK

DATA

ACK

1 - 7

42612 F09

a6 - a0

b7 - b0

1 - 7

ADDRESS

0 0 1 a3:a0

42612 F10

FROM MASTER TO SLAVE

FROM SLAVE TO MASTER

A: ACKNOWLEDGE (LOW)

A: NOT ACKNOWLEDGE (HIGH)

R: READ BIT (HIGH)

W: WRITE BIT (LOW)

S: START CONDITION

P: STOP CONDITION

COMMAND

DATA

X X X X b3:b0

b7:b0

ADDRESS

0 0 1 a3:a0

COMMAND

DATA

X X X X b3:b0

42612 F11

X X X X X X X X

b7:b0

ADDRESS

0 0 1 a3:a0

0 0 1 a3:a0 1 0

COMMAND

ADDRESS

R A

b7:b0 1

DATA

X X X X b3:b0

42612 F12

ADDRESS

0 0 1 a3:a0

0 0 1 a3:a0 1 0

COMMAND

ADDRESS

R A

b7:b0

DATA

X X X X b3:b0

42612 F13

b7:b0

DATA

APPLICATIONS INFORMATION

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