MCP2050 Datasheet, PDF (11/40 Pages) Microchip Technology – LIN Transceiver with Voltage Regulator

1.4 Fail-Safe Features
1.4.1 GENERAL FAIL-SAFE FEATURES
• An internal pull-down resistor on the CS/LWAKE
pin disables the transmitter if the pin is floating.
• An internal pull-up resistor on the TXD pin places
TXD in high, thus the LBUS is recessive if the TXD
pin is floating.
• High-Impedance and low leakage current on LBUS
during loss of power or ground.
• The current limit on LBUS protects the transceiver
from being damaged if the pin is shorted to VBB.
1.4.2 THERMAL PROTECTION
The thermal protection circuit monitors the die
temperature and is able to shut down the LIN
transmitter and voltage regulator.
There are three causes for a thermal overload. A thermal
shut down can be triggered by any one, or a combination
of, the following thermal overload conditions.
• Voltage regulator overload
• LIN bus output overload
• Increase in die temperature due to increase in
environment temperature
The recovery time from the thermal shutdown is equal
to adequate cooling time.
Driving the TXD and checking the RXD pin makes it
possible to determine whether there is a bus contention
(TXD = high, RXD = low) or a thermal overload condition
(TXD = low, RXD = high).
FIGURE 1-7:
THERMAL SHUTDOWN
STATE DIAGRAMS
Output
Overload
LIN bus
shorted
to VBB
Voltage
Regulator
Shutdown
Operation
Mode
Transmitter
Shutdown
Temp < SHUTDOWNTEMP Temp < SHUTDOWN_TEMP
MCP2050
1.4.3
TXD/LBUS TIME-OUT TIMER
LIN bus can be driven to a dominant level either from
TXD pin or externally. An internal timer deactivates the
LBUS transmitter if a dominant status (low) on LIN bus
lasts longer than Bus Dominant Time-Out Time tTO(LIN)
(approximately 20 ms); at the same time, RXD output is
put in recessive (high), FAULT/TXE is also driven to low
and the internal LIN pull-up resistor is disconnected.
The timer is reset on any recessive LBUS status or POR
mode. The recessive status on LBUS can be caused
either by the bus being externally pulled up or by TXD
pin being returned high.
 2012-2014 Microchip Technology Inc.
DS20002299C-page 11