33989 datasheet(46/66 Pages) FREESCALE

46 / 66 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

33989

TYPICAL APPLICATIONS

SUPPLEMENTAL APPLICATION NOTES

Figure 34. 33989 CAN Interface

CAN Interface Supply

The supply voltage for the CAN driver is the V2 pin. The

CAN interface also has a supply path from the battery line,

through the pin VSUP. This path is used in CAN sleep mode

to allow wake-up detection.

During CAN communication (transmission and reception)

the CAN interface current is sourced from the V2 pin. During

a CAN low power mode, the current is sourced from the

VSUP pin.

Main Operation Modes Description

The CAN interface of the MC33989 has two main

operation modes: Normal mode and sleep mode. The modes

are controlled by the SPI command.

In normal mode, used for communication, four different

slew rates are available for the user.

In sleep mode, the user has the option to enable or disable

the remote CAN wake-up capability.

CAN Driver Operation in Normal Mode

When the CAN interface of the MC33989 is in Normal

mode, the driver has two states: recessive or dominant. The

driver state is controlled by the TX pin. The bus state is

reported through the RX pin.

When TX is high, the driver is set in a recessive state,

CANH and CANL lines are biased to the voltage set at V2

divided by 2, approx. 2.5 V.

When TX is low, the bus is set into dominant state: the

CANL and CANH drivers are active. CANL is pulled to gnd,

CANH is pulled high toward 5 V (the voltage at V2).

The RX pin reports the bus state: the CANH minus the

CANL voltage is compared versus an internal threshold (a

few hundred mV). If “CANH minus CANL” is below the

threshold, the bus is recessive and RX is set high.

If “CANH minus CANL” is above the threshold, the bus is

dominant and RX is set low. This is illustrated in the figure

below.

Figure 35. CAN Driver Operation in Normal Mode

Bus termination (60 ohms)

CANH line

CAN L line

Differential

receiver

Driver

2.5V

Wake-up

receiver

pattern

recognition

Internal

VSUP

wake-up

signal

CANH

CANL

SPI control

CANH

2.5V

CANH-DOM

CANH-REC

CANL

2.5V

CANL-DOM

CANL-REC

CANH-CANL

33989 Datasheet(PDF) 46 Page - Freescale Semiconductor, Inc

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