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Analog Integrated Circuit Device Data
Freescale Semiconductor
55
33903/4/5
CAN INTERFACE
CAN INTERFACE DESCRIPTION
CAN INTERFACE
CAN INTERFACE DESCRIPTION
The figure below is a high level schematic of the CAN
interface. It exist in a LS driver between CANL and GND, and
a HS driver from CANH to 5 V-CAN. Two differential
receivers are connected between CANH and CANL to detect
a bus state and to Wake-up from CAN Sleep mode. An
internal 2.5 V reference provides the 2.5 V recessive levels
via the matched RIN resistors. The resistors can be switched
to GND in CAN Sleep mode. A dedicated split buffer provides
a low-impedance 2.5 V to the SPLIT pin, for recessive level
stabilization.
Figure 33. CAN Interface Block Diagram
Can Interface Supply
The supply voltage for the CAN driver is the 5 V-CAN pin.
The CAN interface also has a supply pass from the battery
line through the VSUP/2 pin. This pass 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 5 V-CAN pin.
During CAN LP mode, the current is sourced from the VSUP/
2 pin.
TXD/RXD Mode
In TXD/RXD mode, both the CAN driver and the receiver
are ON. In this mode, the CAN lines are controlled by the TXD
pin level and the CAN bus state is reported on the RXD pin.
The 5 V-CAN regulator must be ON. It supplies the CAN
driver and receiver.The SPLIT pin is active and a 2.5 V
biasing is provided on the SPLIT output pin.
Receive Only Mode
This mode is used to disable the CAN driver, but leave the
CAN receiver active. In this mode, the device is only able to
report the CAN state on the RXD pin. The TXD pin has no
effect on CAN bus lines. The 5 V-CAN regulator must be ON.
The SPLIT pin is active and a 2.5 V biasing is provided on the
SPLIT output pin.
Operation in TXD/RXD Mode
The CAN driver will be enabled as soon as the device is in
Normal mode and the TXD pin is recessive.
Differential
Receiver
Driver
2.5 V
Receiver
Pattern
Detection
CANH
CANL
QH
QL
RIN
VSUP/2
5V-CAN
Failure Detection
Buffer
5V-CAN
SPLIT
Wake-up
& Management
TXD
RXD
5V-CAN
Thermal
SPI & State machine