LTC4331 datasheet(12/26 Pages) AD

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LTC4331

Rev 0

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APPLICATIONS INFORMATION

Overview

Two LTC4331 devices are required for a complete extended

I2C network. Using the REMOTE pin, one LTC4331 is con-

figured to local mode and acts as a full-featured SMBus

compatible I2C slave device. Through this local interface

a master can address a remote slave device up to 1200m

away along a differential cable. On the remote network a

second LTC4331 configured to remote mode acts as an

I2C master device connected to the remote slave devices.

The master interface mirrors the local I2C transactions

on the remote network and transmits the remote slave

responses back to the local network. In most cases the

link is transparent; the remote slave devices appear as

local devices to a local master.

A separate addressable slave device contained in the local

side LTC4331 provides a control interface for optional

configuration and event monitoring of the link.

differential link as an encoded bit-stream to a second

LTC4331 which is set to remote mode. After an I2C bus

turnaround, the device operates as a slave-transmitter

and the differential link direction is reversed. The remote

LTC4331 transmits the response data measured from the

remote I2C bus onto the twisted pair cable. The local side

LTC4331 then decodes the transmitted bit-stream into

I2C data events and drives them onto the local I2C bus.

When operating as a slave-transmitter, the local LTC4331

must periodically stall the local I2C bus to account for

remote I2C bus and link latencies. It does this by clock-

stretching whenever a valid response is not yet available.

Therefore it is recommended that the local I2C mas-

ter device fully support SCL clock-stretching for each

response (N)ACK and data bit. See section Considerations.

By using SCL clock-stretching to account for link and

remote device latency, the local I2C clock rate is decoupled

from the link baud rate and remote I2C clock rate. This

allows independent I2C bus rates between the local and

remote networks.

Remote Mode

On the remote side, set the REMOTE pin high to put the

LTC4331 in remote mode. In this mode the LTC4331

operates as an I2C master device. In normal operation

the remote master mirrors the I2C events produced by

the local I2C master. The device recreates the events using

Fast-mode Plus, Fast-mode, or Standard-mode class tim-

ing specifications. The timing class is selected by pins

SPEED1 and SPEED2.

The LTC4331 does not support multiple masters on the

remote I2C networks. The LTC4331’s I2C master device

interface is the only allowed master on the remote side

network. Remote slaves are also forbidden to switch

to master mode, for example as part of a host-notify

operation.

The LTC4331 master interface fully supports slave device

clock-stretching for all data bits in the packet.

I2C Transactions

A local master initiates a transaction by sending an I2C

START along with the slave address byte. The LTC4331

Figure9. LTC4331 Solution Inserted Into an I2C Network.

REM_SCL

REM_SDA

REM_ALERT

REM_CTRL

MCU_SCL

MCU_SDA

MCU_ALERT

MCU_CTRL

SCL

SDA

ALERT

CTRL

µP

LTC4331

DEVICE

REMOTE

µP

DEVICE

TWISTED PAIR

LOCAL SIDE

REMOTE SIDE

4331 F09

BREAK CONNECTIONS AND INSERT LTC4331 SOLUTION

LOCAL SLAVE

LOCAL MASTER

LOCAL SLAVE

LOCAL MASTER

REMOTE MASTER

REMOTE SLAVE

LOCAL I2C BUS

REMOTE I2C BUS

Local Mode

On the local side, set the REMOTE pin low to put the

LTC4331 in local mode. In this mode the LTC4331 oper-

ates as a slave device. The I2C interface is designed to

be compatible with I2C Fast-mode Plus, Fast-mode, or

Standard-mode class timing specifications selectable

using pins SPEED1 and SPEED2.

When operating as a slave-receiver the LTC4331 cap-

tures I2C START, STOP, and data events sent by a local

I2C master. The device transmits these events across the

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