MCP2022T-330ESLASHP datasheet(13/54 Pages) MICROCHIP

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 2005-2014 Microchip Technology Inc.

DS20002018H-page 13

MCP2021/2/1P/2P

1.4.8

BATTERY POSITIVE SUPPLY

VOLTAGE (VBB)

Battery Positive Supply Voltage pin. This pin is also the

input for the internal voltage regulator.

1.4.9

FAULT/TXE

Fault Detect Output and Transmitter Enable Input

bidirectional pin.

This pin is an open-drain output. Its state is defined as

shown in Table 1-3. The transmitter driver is disabled

whenever this pin is low (‘0’), either from an internal

Fault condition or by external drive. This allows the

transmitter to be placed in an OFF state and still allow

the voltage regulator to operate. Refer to Table 1-1.

The FAULT/TXE also signals a mismatch between the

TXD input and the LBUS level. This can be used to

detect a bus contention. Since the bus exhibits a

propagation delay, the sampling of the internal

compare is debounced to eliminate false faults.

This pin has an internal pull-up resistor of

approximately 750 kΩ. The internal pull-up resistor

may be too weak for some applications. We recom-

mend adding a 10 kOhm external pull-up resistor to

ensure a logic high level.

The FAULT/TXE pin sampled at a rate faster than every

10 µs.

1.4.10

RESET

RESET is an open-drain output pin. This pin reflects an

internal signal that tracks the internal system voltage

has reached a valid, stable level.

As long as the internal voltage is valid, this pin will keep

high-impedance. When the system voltage drops

below the minimum required, the voltage regulator will

shut down and immediately convert the RESET output

to short to GND. A pull-up resistor is needed to change

the output to high/low voltage. When connected to a

microcontroller input, this can provide a warning that

the voltage regulator is shutting down (see Figure 1-2).

Alternately, it can act as an external brown-out by

connecting the RESET output to MCLR (see

Figure 1-2). In addition to monitoring the internal

voltage, RESET is asserted immediately upon entering

the Power-Down mode.

1.4.11

EXPOSED THERMAL PAD (EP)

It is recommended to connect this pad to VSS to

enhance electromagnetic immunity and thermal

resistance.

Note 1:

The FAULT/TXE pin is true (0) whenever

the internal circuits have detected a short

or thermal excursion and have disabled

the LBUS output driver.

FAULT/TXE is true (0) when VREG not OK

and has disabled the LBUS output driver.

TABLE 1-3:

FAULT/TXE TRUTH TABLE

TXD

RXD

Out

LINBUS

I/O

Thermal

Override

FAULT/TXE

Definition

External

Input

Driven

Output

VBB

OFF

FAULT

, TXD driven low, LBUS shorted to VBB

(Note 1)

VBB

OFF

GND

OFF

GND

OFF

, data is being received from the LBUS

VBB

FAULT

, transceiver in thermal shutdown

VBB

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 after approximately 25 µs after TXD falling edge. This is to eliminate false fault

reporting during bus propagation delays.

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