MCP2003 datasheet(11/34 Pages) MICROCHIP

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DS22230D-page 11

MCP2003/4/3A/4A

1.6

MCP2003/4 and MCP2003A/4A

Difference Details

The differences between the MCP2003/4 and the

MCP2003/4A devices are isolated to the wake-up

functionality. The changes were implemented to make

the device more robust to LIN bus conditions, outside

of the normal operating conditions. The MCP2003/4

will wake-up from Power Down Mode during any LIN

falling edge held low longer than 20us.

In the case where a LIN system is designed to

minimize stand-by current by disconnecting all bus

pull-ups resistors (including the external master pull-

up resistor to VBB), the original MCP2003/4 could

wake up, if the floating bus drifted to a valid low level.

The MCP2003/4A revisions were modified to require a

rising edge after a valid low level. This will prevent an

undesired system wake-up in this scenario, while

maintaining functional capability with the original

version.

It should be noted that the original MCP2003/4 meets

all LIN transceiver specification requirements and

modules can be designed to pass all LIN system

requirements. However, when all bus pull-up resistors

are disconnected, the MCP2003/4 requires the

module designer to write firmware to monitor the LIN

Bus after any wake-up event to prevent the transceiver

from automatically transitioning from Ready mode to

Operational mode.

If the MCP2003/4 is placed into Operational mode,

VBB-LBUS pull-up resistor is automatically connected,

which will raise the LIN bus to a recessive level; then

putting the device to Power-Down mode may cause

LBUS to be floating, and thus wake up all bus nodes.

To prevent this, the designer should insure TXD

(MCP2003) or TXE (MCP2004) is held low until valid

bus activity is verified (see Figure 1-6). This will

ensure the transceiver transitions from Ready mode to

Transmitter Off mode, until bus activity can be verified.

In the case of valid bus activity, the transceiver can

shift to Operation mode, while if there is no bus

activity, the device can be again placed into Power

Down. The design practices needed to accomplish this

are fully detailed in Tech Brief TB3067 - “MCP2003

Power-Down Mode and Wake-Up Handling in Case

of LIN Bus Loss” (DS93067).

The revised MCP2003/4A devices now eliminate the

need for firmware to prevent system wide wake-up.

The revised devices now require a longer valid bus

low (see updated tBDB value in the Specification

tables and FIGURE 2-7: “MCP2003A/4A Remote

Wake-up”), which enables a rising edge detect circuit.

The device will now only wake up after a rising edge,

following a low longer than tBDB. While the module

designer can still hold TXD (MCP2003) or TXE

(MCP2004) low during wake-up, to enter Transmitter

Off mode from Ready mode, it is not required to

prevent an advertent system wake-up.

In addition to the longer tBDB value, the time from

wake-up detect to VREN enable is shortened as

documented in the Specification table.

FIGURE 1-6:

MCP2003/2004 Switching Timing Diagram for the Forced Power-Down Mode

Sequence

TXD

VREN

Ready

Mode

Transmitter OFF

Mode

Power Down

Mode after Master

Sleep instruction

Power Down

Mode

tTx2CS >= 100ns

tCSactive >= 100µs

TXD to 0

forced

externally

TXD state depending

on how the Slave

Microcontroller is

powered

LBUS

State

LIN bus

disconnected

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