L9805 datasheet(76/103 Pages) STMICROELECTRONICS

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L9805

5.7 CAN BUS TRANSCEIVER

5.7.1 Introduction

The CAN bus transceiver allows the connection of

the microcontroller, with CAN controller unit, to a

CAN bus. The transmitter section drives the CAN

bus while the receiver section senses the data on

the bus.

The CAN transceiver meets ISO/DIS 11898 up to

1 MBaud.

5.7.2 Main Features

TRANSMITTER:

– Generation of differential Output signals

– Short Circuit protection from transients in auto-

motive environment

– Slope control to reduce RFI and EMI

– High speed (up to 1Mbaud)

– If un-powered, L9805 CAN node does not disturb

the bus lines (the transceiver is in recessive

state).

RECEIVER:

– Differential input with high interference suppres-

sion

– Common mode input voltage range (VCOM) from

-5 to 12V

5.7.3 Functional Description

The Can Bus Transceiver is used as an interface

between a CAN controller and the physical bus.

The device provides transmitting capability to the

CAN controller. The transceiver has one logic in-

put pin (TX), one logic output pin (RX) and two In-

put/Output pins for the electrical connections to

the two bus wires (CAN_L and CAN_H). The mi-

crocontroller sends data to the TX pin and it re-

ceives data from the RX pin. The transmission

slew-rates of CAN_H and CAN_L voltage are con-

trolled to reduce RFI and EMI. The transceiver is

protected against short circuit or overcurrent: If

ICANH and/or ICANL exceeds a current thresholds

ISC, then the CAN_H and CAN_L power transis-

tors are switched off and the transmission is disa-

bled for TD=25µs typical.

5.7.4 CAN Transceiver Disabling function

The transceiver can be disabled and forced to

move in a low power consumption mode, setting

CANDS bit in DCSR register (see Section 3.2.1).

When the transceiver is in this mode it can not re-

ceive nor transmit any information to the bus. The

only way to have again on board the CAN capabil-

ities is reset CANDS bit. The CAN protocol handler

can not disable nor enable the transceiver and

there is no way to communicate to the controller

the transceiver is down. The disabling function has

the only purpose to allow the reduction of the cur-

rent consumption of the device in application not

using the CAN at all or using it for particular func-

tions (such like debugging). Current consumption

reduction, when disabling the trasceiver, can be as

high as 15mA.

Note When the CAN capabilities of L9805 are not

needed additional consumption reduction can be

achieved putting the CAN controller in Stand-by

Mode (see Section 5.6.3.3).

Figure 40. Can Bus Transceiver Block Diagram

ŠŠ

−

TX0

RX0

CAN_H

CAN_L

OVERCURRENT

DETECTION

OVERCURRENT

DETECTION

POWER

CONTROL

VDD

GND

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