LTC4331 datasheet(15/26 Pages) AD

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LTC4331

Rev 0

For more information www.analog.com

APPLICATIONS INFORMATION

world hazards. The LTC4331 passes the following tests

on the A, B pins:

• IEC 61000-4-2 Edition 2.0 2008-12 ESD Level 4: ±8kV

contact (A or B to GND, direct discharge to bus pins

with transceiver and protection circuit mounted on a

test card with a low impedance ground discharge path

from board GND to ESD gun return lead, per Figure 4

of the standard)

• IEC 61000-4-4 Second Edition 2004-07 EFT Level 4:

±5kV (A or B to GND, 5kHz repetition rate, 15ms burst

duration, 60 second test duration, discharge coupled

to bus pins through 100pF capacitor per paragraph

7.3.2 of the standard). VCC pin requires a low induc-

tance capacitor of at least 4.7µF to meet Level 4 rating.

Startup and Shutdown

Startup occurs when supply voltages are applied to pins

VCC and VL and the ON pin is high. All output pins are tri-

stated during the first part of startup. After an initialization

sequence, the I2C interface and other pins are functional.

The local side LTC4331 monitors the I2C bus for inactivity

and probes the differential link. When the device detects

an idle condition on the local I2C bus, it drives pin RDY

low to indicate that it is ready to respond to I2C transac-

tions. Thereafter a master can access the internal control

interface. In addition, once the device establishes link

communication with a remote LTC4331, it drives pin LINK

low and the remote I2C network can be accessed.

The ON pin can be used to set the LTC4331 to a lower

power state. By setting ON low, the LTC4331 is held in

reset, all programmed configuration is set to the default

value, all output drivers are disabled, and the differential

transceiver is put into low power mode. If not used, tie

ON to VL.

Link Status

The LTC4331 provides the LINK pin which indicates if the

remote I2C network has joined with the local I2C network.

LINK is driven low when bidirectional link communica-

tion is established and the I2C interface is ready. It is an

open-drain output and requires an external pull-up to VL

if used. At startup, the LINK pin output driver is disabled.

Link status can also be monitored using the control inter-

face. See section Control Interface.

Ensure that the values set on local side SPEED1 and

SPEED2 pins match the values set on remote side. Also,

do not exceed the cable length listed in Table 2 for the

given SPEED setting. The LTC4331 will not link if these

conditions are not met.

Note that the link status is indeterminate if the REMOTE

pin is incorrectly configured on either the local or remote

side LTC4331 device.

Ready Status

The RDY pin is driven low when the local side LTC4331

control interface is ready for access. It is an open-drain

output and only valid in local mode. When the device is

first powered and pin ON is set high, the low output driver

on RDY is disabled and the pin is weakly pulled to VL. An

internal I2C bus idle detection circuit prevents the interface

from interrupting an active transaction. This circuit drives

RDY low when either pin SCL is high for tREADY:IDLE or it

detects an I2C STOP which indicates the interface is ready

and has joined the bus. The status of the link connection

does not affect the ready function. If pin LINK is high when

RDY is low, only the local side LTC4331 control interface

is available for access. The RDY pin is internally pulled to

VL. It is valid only in local mode.

A secondary function of RDY indicates if the internal buf-

fer has filled, see section Considerations for more detail.

Interrupt/SMBALERT

The LTC4331 supports an interrupt signal that is mirrored

from the remote network to the local network using the

differential link. On the remote side ALERT is an input pin

that can be connected to remote I2C slave devices. While

on the local side ALERT operates as an open-drain type

output that can be connected to a shared local interrupt

line. ALERT is periodically sampled and has a propagation

time of tALT_PROP.

If enabled, the local LTC4331’s control interface uses the

ALERT pin to report link and fault events. The local side

ALERT output is the logical AND of the remote ALERT and

the internal endpoint interrupt signal.

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