MCP2050T-ESLASHP datasheet(11/40 Pages) MICROCHIP

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 2012-2014 Microchip Technology Inc.

DS20002299C-page 11

MCP2050

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

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.

Operation

Mode

Transmitter

Shutdown

LIN bus

Voltage

Shutdown

Regulator

Output

Temp < SHUTDOWNTEMP

shorted

to VBB

Overload

Temp < SHUTDOWN

TEMP

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