LTC4331 datasheet(17/26 Pages) AD

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LTC4331

Rev 0

For more information www.analog.com

APPLICATIONS INFORMATION

Figure13. SCL Frequency Range when the I2C

Master Ignores Slave SCL Low Stretching

side, the LTC4331 acting as an I2C master also releases

SCL and SDA if an remote slave is signaling a timeout. In

addition, the LTC4331 master sends a STOP event and

requires a local side STOP event before allowing further

remoteI2Ctransactions.Thisensuresthelocalandremote

are synchronized.

Inaddition,thelocalsideLTC4331slaveinterfacecontains

an SDA stuck-low prevention circuit which ensures the

LTC4331 does not hold SDA low when the I2C bus is idle.

This typically occurs when there is a loss of I2C protocol

synchronization between the master and slave devices.

If the LTC4331 is holding SDA low while SCL is high for

35ms, the interface is reset and SDA is released.

Remote Stuck Bus Protection

On the remote side, the LTC4331 master device can detect

and attempt recovery from I2C bus faults. If the master

device senses that SDA is low when it should be high,

it considers SDA stuck by a slave device. The LTC4331

enters a bus recovery routine which drives 16 SCL clocks

onto the bus and then issues a STOP event. This routine

is also entered if SDA is sensed low after a startup. If

successful, the LTC4331 master then ignores further

local I2C bus transactions until the local bus transmits a

STOP condition. If the routine is unsuccessful, it retries

whenever a local side master initiates a new transaction.

If the remote LTC4331 detects that SCL is stuck, it auto-

matically NACKs all I2C transactions from the local bus

until it measures SCL high and receives a STOP command

from a local I2C master.

For both SCL and SDA fault conditions, the remote

LTC4331 sends a FAULT response to the local LTC4331

which sets the EXT_I2C_FAULT EVENT bit.

Remote Reset

The local side LTC4331 can trigger a remote side LTC4331

reset by holding the ON pin low for a minimum of tREMOTE_

RESET. In addition, the remote LTC4331 is automatically

reset after tREMOTE_RESET if the link is disconnected. A

remote reset disables all remote side outputs, including

pin CTRL, until link communication is reestablished.

Considerations

• The LTC4331 relies on SCL clock-stretching to account

for link and remote bus latencies. Using a local master,

either hardware or software based, that fully supports

clock-stretching is highly recommended for best per-

formance. Alternately, the SCL frequency can also be

reduced such that the LTC4331’s SCL configured

low time and remote response time is less than the

master’s programmed SCL low time. The total clock-

stretching time of the local LTC4331 I2C slave device

depends on SPEED1 and SPEED2 pin settings and

remote I2C Slave device timing requirements. This is

not recommended. See Figure13.

Table1. Known I2C Master Devices Incompatible with

LTC4331 SCL Clock-Stretching

DEVICE

ISSUE

WORKAROUND

All Raspberry Pi

models (Broadcom

BCM283X)

Hardware I2C

peripheral clock-

stretching issues

Use software based

I2C that fully supports

SCL clock-stretching

Analog Devices

DC590B QuikEval

controller

SCL signal path is

not bidirectional

Use Analog Devices

Linduino® w/DC590

sketch

• The LTC4331 I2C Slave Extender does not support

remote I2C devices acting as masters. Therefore the

SMBus Address Resolution Protocol and Host Notify

Protocol are not supported.

• When using SMBus ARA, if there are SMBus slave

devices on the local and remote side of the extender,

30m

600m

SPEED INDEX

100

4331 F13

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