MCP2003-ESLASHSN datasheet(11/34 Pages) MICROCHIP

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DS20002230F-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 func-

tionality. 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 20 µs.

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 ris-

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

undesired system wake-up in this scenario, while main-

taining functional capability with the original version.

It should be noted that the original MCP2003/4 meets

all LIN transceiver specification requirements and mod-

ules can be designed to pass all LIN system require-

ments. 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

to 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

ensure

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 Section 2.3 “DC Specifi-

cations”

and Figure 2-7), 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 Transmit-

ter 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 Section 2.3 “DC Specifications”.

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 100 ns

tCSactive 100 µs

TXD to

forced

externally

TXD state depending

on how the Slave

Microcontroller is

powered

LBUS

State

LIN bus

disconnected

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