Detailed Description

The MAX13041 ±80V fault-protected, high-speed CAN

transceiver is intended for high-speed industrial and

automotive network applications where high reliability

and advanced power management are required. The

device links a CAN protocol controller to the physical

bus wires of the controller area network (CAN) and

allows communication at speeds up to 1Mbps. Built-in

level shifting allows for direct connection to protocol con-

trollers operating from lower voltages. The extended

fault-protected voltage range of ±80V on CAN bus lines

allows for use in +12V or +42V automotive, and higher

voltage +24V and +36V heavy-duty truck applications.

Advanced power management features make the

MAX13041 ideal for automotive electronic control unit

(ECU) modules that are permanently supplied by bat-

tery, regardless of the ignition switch position (clamp-

30, type-A modules). The device controls one or more

external voltage regulators to provide a low-power

sleep mode for an entire clamp-30 node. Wake-on CAN

capability allows the MAX13041 to restore power to the

node upon detection of CAN bus activity. The

MAX13041 is functionally compatible with the Philips

TJA1041A and is a pin-to-pin replacement with

improved performance.

CAN Interface

The ISO11898 specification describes the physical

layer of a controller area network (CAN). A CAN imple-

mentation is comprised of multiple transceiver modules

linked by a pair of bus wires. Communication between

modules occurs through transmission and reception of

differential logic states on the bus lines. Two compli-

mentary logic states are defined by ISO11898. A domi-

nant state results when the differential voltage on the

CAN bus lines is greater than 0.9V. A recessive bus

state results when the differential voltage is less than

0.5V (Figure 1). The CAN bus exhibits a wired-AND

characteristic, meaning the bus is only recessive when

all connected transmitters are recessive. Any transmit-

ter asserting a dominant logic state forces the entire

CAN bus dominant.

The MAX13041 accepts logic-level data from the CAN

protocol controller on TXD. Drive TXD low to assert a

dominant state on the CAN bus. Drive TXD high to

release the CAN bus to a recessive state. TXD is inter-

sented to the protocol controller as a logic level on

RXD. The MAX13041 receiver remains active during

transmission to allow for the bit-wise arbitration scheme

specified by the CAN protocol.

Level Shifting

The MAX13041 provides level shifting on TXD, RXD,

EN,

STB, WAKE and ERR for compatibility with lower-

voltage protocol controllers. Set the interface logic lev-

els for TXD, RXD, EN,

STB, WAKE, and ERR by

controller, or another voltage from +2.8V to +5.25V.

Split-Termination and Common-Mode

Voltage Stabilization

The CAN bus specification requires a total bus load resis-

tance of 60Ω. Each end of the bus should be terminated

with 120Ω, the characteristic impedance of the bus line.

Electromagnetic emission (EME) is reduced by a split-ter-

mination method, whereby each end of the bus line is ter-

minated by 120Ω split into two 60Ω resistors in series

(see Figure 3). A bypass capacitor shunts noise to

ground from the node connecting the 60Ω resistors.

When the CAN bus is recessive, the common-mode

voltage is pulled low by the leakage current from inac-

tive modules. When the CAN bus subsequently goes

dominant, the proper common-mode voltage is

restored by the transmitting device. A common-mode

voltage step results, generating excessive EME. To mit-

igate this problem, the common-mode voltage of the

node (see Figure 3). During normal and PWON/listen-

on SPLIT. Connect SPLIT to the node connecting the

two 60Ω termination resistors to stabilize the common-

mode voltage of the bus and prevent EME from com-

mon-mode voltage steps.

Power-Management Operating Modes

The MAX13041 provides advanced power management

for a clamp-30 node by controlling one or more external

voltage regulators. Five operating modes provide differ-

ent functionality to minimize power consumption.

±80V Fault-Protected High-Speed CAN Transceiver

with Low-Power Management and Wake-On CAN

______________________________________________________________________________________

11

SPLIT

CANH

CANL

60

Ω

60

Ω

Figure 3. Biased Split Termination