normal mode, prior to the fourth dominant-to-recessive
transition on TXD. A low level on ERR indicates a local
wake-up has occurred.
Bus Failure Flag
The bus failure flag is set when the MAX13041 detects
a CAN bus short-circuit to V
BAT
, V
CC,
or GND for four
consecutive dominant-recessive cycles on TXD. The
flag is cleared when the MAX13041 leaves normal
mode. The bus failure flag is externally indicated as a
logic low on ERR in normal mode, after the fourth domi-
nant-to-recessive transition on TXD.
Local Failure Flag
The local failure flag indicates five separate local failure
conditions (see
Fault Protection & Fail-Safes
section).
When one or more local failure conditions have
occurred, the local failure flag is set. The flag is cleared
when the MAX13041 enters normal mode or when RXD
goes logic-low while TXD is logic-high. The local failure
flag is externally indicated as a logic-low on ERR when
the MAX13041 is placed into PWON/listen-only mode
from normal mode.
Wake-On CAN
The MAX13041 provides wake-on-CAN capability from
sleep mode. When the MAX13041 detects two domi-
nant bus states, each followed by a recessive state
(Figure 5), the MAX13041 sets the wake-up flag and
enters an operating mode determined by the state of
EN and STB. Each CAN logic state must be at least 5µs
in duration. This wake-up detection criterion serves to
prevent unintentional wake-up events due to bus faults
such as V
BAT
to CANH or an open circuit on CANL. At
higher data rates (>125kbit/s), wake-up can not be
guaranteed for a single, arbitrary CAN data frame. Two
or more consecutive arbitrary CAN data frames may be
required to ensure a successful wake-on-CAN event.
External-Voltage Regulator Control
MAX13041 controls one or more external voltage regu-
lators through INH, a V
BAT
-referenced, open-drain out-
put. When INH is logic-high, any external voltage
regulators are active and power is supplied to the
node. When INH is high-impedance, the typical pull-
down characteristic of the voltage-regulator inhibit input
pulls INH to a logic-low and disables the external volt-
age regulator(s).
Fault Protection & Fail-Safes
The MAX13041 features ±80V tolerance on CAN bus
lines CANH, CANL, and SPLIT. Up to +76V operation is
possible on V
BAT
, allowing for use in +42V automotive
applications. Additionally, the device detects local and
remote bus failures and features fail-safe modes to
prevent damage to the device or interference with CAN
bus communication.
The MAX13041 detects five different local faults. When
any local fault is detected, the local failure flag is set.
Additionally, for faults other than bus dominant clamp-
ing, the transmitter is disabled to prevent possible dam-
age to the device. The transmitter remains disabled
until the local failure flag is cleared.
TXD Dominant Clamping
An extended logic-low level on TXD due to hardware or
software failure would ordinarily clamp the CAN bus to
a dominant state, blocking communication on the entire
bus. This condition is prevented by the TXD dominant
time-out feature. If TXD is held low for longer than
t
DOM(TXD)
, the local failure flag is set and the transmit-
ter is disabled until the local failure flag is cleared. The
TXD time-out value limits the minimum allowable bit rate
to 40kbps.
RXD Recessive Clamping
If a hardware failure clamps RXD to a logic-high level,
the protocol controller assumes the CAN bus is in a
recessive state at all times. This has the undesirable
effect that the protocol controller assumes the bus is
clear and may initiate messages that would interfere with
ordinary communication. This local failure is detected by
checking the state of RXD when the CAN bus is in a
dominant state. If RXD does not reflect the state of the
CAN bus, the local failure flag is set and the transmitter is
disabled until the local failure flag is cleared.
TXD-to-RXD Short-Circuit Detection
A short-circuit between TXD and RXD forces the bus
into a permanent dominant state upon the first transmis-
sion of a dominant bit because normally the low-side
driver of RXD is stronger than the microcontroller high-
side driver of TXD. The MAX13041 detects this condi-
tion and prevents the resulting bus failure by setting the
local failure flag and disabling the transmitter. The
transmitter remains disabled until the local failure flag is
cleared.
Bus Dominant Clamping
A short-circuit fault from the CAN bus to V
BAT
, V
CC
, or
GND could produce a differential voltage between
CANH and CANL greater than the receiver threshold,
resulting in a dominant bus state. If the bus state is
clamped dominant for longer than t
DOM(BUS)
, the local
failure flag is set. The transmitter is not disabled by this
fault and the local failure flag is cleared as soon as the
bus state becomes recessive.
MAX13041
±80V Fault-Protected High-Speed CAN Transceiver
with Low-Power Management and Wake-On CAN
______________________________________________________________________________________ 15
