MLX80001 Datasheet, PDF (17/28 Pages) Melexis Microelectronic Systems – 4-channel Master LIN Transceiver

MLX80001
4-channel Master LIN Transceiver
4. Fail-save Features
Loss of battery
If the ECU is disconnected from the battery, the LIN pin is in high impedance state. There is no impact to the
LIN bus traffic and to the ECU self, no damage can occur.
Loss of Ground
In case of an interrupted ECU ground connection the LIN pin is in high impedance state. There is no impact
to the LIN bus traffic and to the ECU self, no damage can occur.
Short circuit to battery
The transmitter output current is limited to the specified value in case of short circuit to battery in order to
protect the MLX80001 itself against high current densities. Otherwise the micro of the master ECU or the
slave nodes will not detect any bus traffic until the failure disappears and will switch into sleep mode.
Ground shift and short circuit to ground
If the LIN wire is shorted to negative shifted ground levels, there is no current flow from the ECU ground to
the LIN bus and no distortion of the LIN bus traffic.
A permanent failure current from battery via LIN short to ground can be reduced dramatically by
disconnection of the master pull up resistor. The following different situations may occur:
• The master node is in sleep mode, there is no bus traffic at any channel. If a short circuit to ground is
applied to a LIN network, the H ->L transition will awakens the shorted LIN network and the master
node. Due to the wake up source recognition the master is able to detect the wake up channel and
will not awaken the other LIN networks too. If there is no bus traffic possible with the shorted
network, the connected nodes will go to sleep mode again and the failure current to ground is
limited. If the failure disappears, the high resistive termination is able to drive a recessive voltage
level and the master node and the network will wake up due to the L->H transition.
• The master node is busy and there is bus traffic on one or more connected LIN networks. If a short
circuit to ground is applied to a LIN network, the integrated RxD timeout circuit will disconnect the
master pull up resistor from the shorted LIN network (high resistive termination present now). The
failure current to ground is limited and the thermal overload condition of the MLX80001 is removed
without any intervention of the micro. If the failure disappears, the RxD L->H transition will reset the
RxD timer circuit and the master termination will be reconnected to the LIN network.
Thermal overload
The MLX80001 is protected against thermal overloads.
Independent from the source of a LIN bus transmission (master channel1...4 or any slave node), the most
significant part of the power dissipation will be produced in the master pull up resistor(s) during normal
operation. Assuming a duty cycle of 50% and all channels are busy by bus traffic, the chip only can exceed
the specified trip off temperature if the ambient temperature is higher than the specified maximum of125°C.
Due to failure situations such as short of a LIN channel vs. battery voltage or ground, the power dissipation
can become higher than expected in the operating temperature range.
In these situations any transmit path will be interrupted and any master pull up resistor will be disconnected
from the LIN interfaces until thermal recovery, independent from the operating mode of the MLX80001 and
without any intervention of the micro. The thermal shutdown can be detected by the micro due to the active
low interrupt applied to any RxD output.
Usually the short to ground situation is covered by the sleep mode behaviour or the RxD timeout feature for
each channel. Thereby very high system availability is guaranteed.
MLX80001 – Datasheet
3901080001
Page 17 of 28
March 2007
Rev 001