LTC4151/LTC4151-1

10

41511fa

Using Optoisolators with LTC4151-1

The LTC4151-1 splits the SDA line into SDAI (input)

and SDAO (inverted output) for convenience of opto-

coupling with a host controller that sits at a differ-

ent ground level. When using optoisolators with the

LTC4151-1, connect the SDAI to the output of the

incoming optocoupler and connect the SDAO to the anode

of the outgoing optocoupler (see Figure 9). With the

outgoing optocoupler clamping SDAO and internal 6V

(5.5V minimum) clamps on SDAI and SCL, the pull-up

resistors on these three pins can be directly connected

SDAO), the need for a separate low voltage supply for

pull-ups is eliminated.

Start and Stop Conditions

in the high state. A bus master signals the beginning of a

transmission with a Start condition by transitioning SDA

from high to low while SCL stays high. When the master

has finished communicating with the slave, it issues a

Stop condition by transitioning SDA from low to high

while SCL stays high. The bus is then free for another

transmission.

Stuck-Bus Reset

bus reset timer. The low conditions of the SCL and the

SDA/SDAI pins are OR’ed to start the timer. The timer is

reset when both SCL and SDA/SDAI are pulled high. If the

SCL pin or the SDA/SDAI pin is held low for over 33ms,

machine will be reset to allow normal communication after

the stuck-bus condition is cleared. The stuck-bus timer

can be disabled by clearing control register bit G2.

ing the three-state pins ADR0 and ADR1, as shown in

Table 1. Address bits a6, a5 and a4 are configured to

(110) and the least significant bit is the R/W bit. In addi-

tion, the LTC4151 and LTC4151-1 will respond to a mass

write address (1100 110)b for writing to all LTC4151s

and LTC4151-1s, regardless of their individual address

settings.

APPLICATIONS INFORMATION

41511 F09

3.3V

0.02Ω

μ-Controller

LTC4151-1

SCL

SCL

48V

2

3

4

SDAI

ADIN

ADR1

R5

0.51k

R6

10k

R7

10k

R4

0.51k

R1

20k

R2

20k

R3

5.1k

1

8

2

7

3

6

4

5

8

1

7

2

6

3

5

4

6

110

7

8

5

9

SDA

ADR0

GND

SDA0

MOCD207M

MOCD207M