MCP8026 datasheet(36/64 Pages) MICROCHIP

36 / 64 page

MCP8025/6

DS20005339B-page 36

 2016 Microchip Technology Inc.

The FAULT/TXE pin will go low whenever the internal

circuits have detected a short circuit and have disabled

the LIN_BUS output driver. The MCP8025 limits the

transmitter current to less than 200 mA when a short

circuit is detected. If the host MCU is driving the

FAULT/TXE pin high, then the transmitter will remain

enabled and the fault condition will be overruled. If the

host MCU is driving the pin low or is in High Z mode,

the MCP8025 will drive the pin low and will disable the

LIN transmitter.

4.5.1.3

LIN Dominant State Timeout

The MCP8025 has an additional LIN feature, LIN

Dominant State Timeout, that is not in the current LIN

2.0 specification. If the LIN TX pin is externally held low

for more than the time specified by tDOM_TOUT, the

MCP8025 will disable the LIN transmitter. The

FAULT/TXE pin will go low, indicating a LIN Dominant

State Timeout fault. Forcing the FAULT/TXE pin high

will not re-enable the transmitter. The transmitter will

stay disabled until the TX pin is set high again. This

prevents the LIN transceiver from inadvertently locking

up the bus.

4.5.2

LEVEL TRANSLATOR (MCP8026)

The level translators are an interface between the

companion microcontroller’s logic levels and the input

voltage

levels

from

the

system.

Automotive

applications typically drive the inputs from the Engine

Control Unit (ECU) and the ignition key on/off signals.

The level translators are unidirectional translators.

Signals on the high-voltage input are translated to

low-voltage signals on the low-voltage outputs. The

high-voltage HV_IN[1:2] inputs have a configurable

30 k

 pull up. The pull up is configured via a

SET_CFG_0

message. The PU30K bit in the

CFG0 register controls the state of the pull up. The bit

may only be changed when the CE pin is low. The

low-voltage LV_OUT[1:2] outputs are open-drain

outputs. The outputs are capable of sinking a minimum

of 1 mA of current while maintaining less than 50 mV at

the output.

The HV_IN1 translator is also used to wake up the

device from the Sleep mode whenever the HV_IN1

input is transitioned to a low level for a minimum of

250 µs followed by a transition to the high voltage level.

TABLE 4-6:

FAULT/TXE TRUTH TABLE

Out

LIN_BUS

I/O

FAULT/TXE

Definition

External

Input

Driven

Output

VDD

High Z

FAULT

, TX driven low, LIN_BUS shorted to VDD (Note 1)

VDD

FAULT

, Overridden by CPU driving FAULT/TXE high

VDD

High Z, H

GND

High Z, H

, data is being received from the LIN_Bus

GND

High Z, H

GND

 V

High Z, H

FAULT

, if TX is low longer than tDOM_TOUT

VDD

NO FAULT

, the CPU is commanding the transceiver to

turn off the transmitter driver

Legend:

x = don’t care

Note 1:

The FAULT/TXE is valid approximately 25 µs after the TXD falling edge. This helps eliminate false fault

reporting during bus propagation delays.

Note:

The TQFP package has two level

translators. The second level translator

typically interfaces to an ignition key on/off

signal.

MCP8026 Datasheet(PDF) 36 Page - Microchip Technology

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