33889 Datasheet, PDF(30/60 Page) Freescale Semiconductor, Inc – System Basis Chip with Low Speed Fault Tolerant CAN Interface

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33889 Datasheet, PDF (30/60 Pages) Freescale Semiconductor, Inc – System Basis Chip with Low Speed Fault Tolerant CAN Interface

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FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

CAN TRANSCEIVER DESCRIPTION

Vsup

RXD

VSE-H (1.85V)

CANH

CANL

VSE-L (3.05V)

Rx multiplexer

Failure detection

Driver

Stvbat

Vdiff

SRL

SRH

TXD

Tx driver

Driver

CAN

SPI

mode control

Vwake-H (2V)

Hwake

CANL

CANH

Lwake

Vwake-L (3V)

CANH

RTL

RtL

RTH

RtH

CANL

GND

Figure 12. Simplified Block Diagram of the CAN Transceiver of the MC33889

General description

CAN driver:

The CANH driver is a âhigh sideâ switch to the V2 voltage

(5V). The CANL driver is a âlow sideâ switch to gnd.The turn

on and turn off time is controlled in order to control the slew

rate, and the CANH and CANL driver have a current limitation

as well as an over temperature shutdown.

The CAN H or CANL driver can be disabled in case a

failure is detected on the CAN bus (ex: CANH driver is

disabled in case CANH is shorted to VDD). The disabling of

one of the drivers is controlled by the CAN logic and the

communication continues via the other drivers. When the

failure is removed the logic detects a failure recovery and

automatically reenables the associated driver.

The CAN drivers are also disabled in case of a Tx failure

detection.

Bus termination:

The bus is terminated by pull up and pull down resistors,

which are connected to GND, VDD or VBAT through

dedicated RTL and RTH pins and internal switches Srh, Srl,

Stvbat. Each node must have a resistor connected between

CANH and RTH and between CANL and RTL. The resistor

value should be between 500 and 16000 ohms.

Transmitter Function

CAN bus levels are called Dominant and Recessive, and

correspond respectively to Low and High states of the TX

input pin.

Dominant state:

The CANH and CANL drivers are on. The voltage at CANL

is <1.4V, the voltage at CANH is >3.6V, and the differential

voltage between CANH and CANL line is >2.2V (3.6V-1.4V).

Recessive state:

This is a weak state, where the CANH and CANL drivers

are off. The CANL line is pulled up to 5V via the RTL pin and

RTL resistor, and the CANH line is pull down via the RTH and

RTH resistor. The resultant voltage at CANL is 5V and 0V at

CANH. The differential voltage is -5V (0V - 5V). The

recessive state can be over written by any other node forcing

a Dominant state.

33889

Analog Integrated Circuit Device Data

Freescale Semiconductor

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