LTC4331 datasheet(12/22 Pages) AD

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LT3960

Rev. B

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OPERATION

The LT3960 is a high-speed transceiver which creates the

functional equivalent of a single-master I2C bus in the CAN

physical layer and is powered from a single wide-ranging

input voltage. Using two integrated CAN transceivers, the

LT3960 creates a differential proxy for each of the sin-

gle-ended I2C clock and data signals which is capable

of traversing harsh or noisy environments across two

twisted pairs.

Each transceiver consists of a transmitter and receiver,

capable of quickly converting a single-ended I2C domi-

nant signal into a differential dominant signal, and vice

versa. The transmitter is a current-regulated differential

driver that generates a differential voltage between the

CANxH and CANxL pins determined by drive current and

the equivalent resistive load on the CANx bus. Common-

mode voltage of the CANx bus is regulated by the trans-

mitter when driving dominant as described in the applica-

tions section. The receiver is a CAN compatible differential

receiver with a wide common-mode range of ±25V or

±36V, depending on VCC voltage.

In the simplest setup, two LT3960 devices are used

(Figure 7). The first is connected to the I2C master (micro-

controller or otherwise). The second LT3960 is connected

to the first by two twisted pairs and regenerates the I2C

bus locally for one or more I2C slave devices. The LT3960

devices transmit the clock signal in only one direction,

from master to slave. Bidirectional communication of the

data signal is always permitted.

The LT3960 contains an integrated LDO which regulates

an input from the VIN pin between 4V and 60V to 3.3V on

the VCC pin from which the transceivers and bus lines are

powered. Alternatively, the LT3960 can by powered from

a supply voltage of 3.3V or 5V on VIN, bypassing the LDO

by shorting VCC to VIN.

The EN/MODE pin is used to put the LT3960 in low power

shutdown mode and selects between Master and Slave

modes of operation when enabled. When the EN/MODE

pin is below 0.7V, (typical) the LT3960 is in shutdown

mode, disabling both the LDO and transceivers. When

VIN is powered, floating the EN/MODE pin or driving it

between 0.7V and 2.0V (typical) enables the LDO and

sets the transceiver in Slave Mode. An EN/MODE voltage

above 2.0V (typical) with VIN is powered sets the LT3960

in Master Mode.

Bidirectional communication is supported on the data

channel (SDA and CANSDA) regardless of the mode of

operation. Communication on the clock channel (SCL

and CANSCL) is unidirectional, with the direction deter-

mined by the selected mode of operation. In Slave Mode,

an LT3960 only communicates clock signals from the

CANSCL bus to the SCL bus. Any LT3960 connected to

slave I2C devices should be operated in Slave Mode. In

Master Mode, an LT3960 only communicates clock sig-

nals from the SCL bus to the CANSCL bus. The LT3960

connected to the I2C master device should always be

operated in Master Mode. Regardless of the number of

LT3960 devices tied to a I2CAN bus in a given applica-

tion, exactly one will operate in Master Mode, driving the

clock signal to the I2CAN bus and, ultimately, to all I2C

slave devices. The LT3960 does not support multi-master

I2C systems.

LT3960

VIN

3960 F07

VCC

SDA

SCL

CIRCUIT BOARD 2

CIRCUIT BOARD 1

CANSDAH

CANSDAL

CANSCLH

CANSCLL

LT3960

VIN

VCC

SDA

SCL

EN/MODE

3.3V OR 5V

4V TO 60V

CANSDAH

CANSDAL

CANSCLH

CANSCLL

SDA

SCL

SDA

SCL

DIG I/O

EN/MODE

I2C

SLAVE

µCONTROLLER

GND

Figure 7. Simple Single-Slave Application

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