MCP2003-E/MD - Microchip Technology

TB3067

INTRODUCTION

This tec hnical brief gi ves a descript ion of how to set the

MCP2003 in Power-Down mode in the case of a LIN

bus loss, which means the voltage level on LBUS falls

down to VIL. This situation could happen if the bus

Master microcontroller disconnects the termination

pull-up resistor (typically 1 kΩ) from t he bus to redu ce

the current consumption in the bus Power-Down state.

Additionally, this technical brief describes the wake-up

procedure when the Master puts the LIN bus back into

Operati on mode.

Holdi ng the MCP2003 in power dow n in the ca se of LIN

bus loss is called “Forced Power-Down mode” in the

further description of this document.

THEORY OF OPERATION

The MCP2003 is a bidirectional, half-duplex

communication physical interface for automotive and

industri al LIN systems to meet the LIN bus specification

Revision 2.1 and SAE J2602. The MCP2003 provides

a physic al in terfa ce betw ee n a mi croc on trol ler and LIN

bus.

FIGURE 1: MCP2003 Block Diagram.

The MCP2003 can be put in Power-Down mode from

Operation mode or Transmitter-Off mode (TOFF Mode)

on the falling edge on CS.

On bus activ ity, or when CS is set to ‘1’, the device will

immediately wake up from Power-Down mode and

enter Ready mode.

Bus activity means that LBUS voltage has dropped

down to V IL for longer than the Bus Activity Debounce

time (tBDB).

This could be caused by the following events:

• Los s/sho rt to G ND

• Wake-up sequence

• Sync b reak

This behavior is necessary to react immediately on a

LIN bus disconnection or LBUS short circuit to ground

(e.g. cable break or wrong plug-in). Additionally, the

devi ce also w akes up on a L IN bus l oss situat ion, wh ich

could be an undesired behavior in certain LIN bus

systems.

Author: Frank Ziegenhorn

Microchip Technology Inc.

MCP2003 Power-Down Mode and Wake-Up

Hand ling in the Ca se of LIN Bus Loss

TB3067

To pre vent an undesir ed wake-up scena rio in a LIN bus

loss situ ation, the Power-Down mode has to be entered

via the T ra nsmitter-Of f mode observ ing specific t imings

and the switching sequence outlined below (“Forced

Power-Down mode”).

The following state machine diagram shows the paths

to enter the MCP2003 Power-Down mode from

Operation mode or Transmitter-Off mode.

To enter Power-Down mode from Ready mode, the

MCP2003 has two different paths:

• Passing through Transmitter-Off mode (TOFF),

which is shown in red in Figure 2

• Pa ssing th rough O perati ng mode, whi ch is shown

in blue in Figure 2

FIGURE 2: Entering MCP2003 Power-Down Mode From Operation Mode or T ransmitter-Off Mode.

The Forced Power-Down mode sequence is used to

enter Power-Down mode without activating the

transceiver to reduce the current consumption of the

transceiver . After the device is in Ready mode, this path

could be selected by holding TXD and CS in low state

for tTX2CS, and then setting CS to ‘1’ for tCSactive

before resetting CS to ‘0’. This results in all functiona lity

being disabled in the transceiver until CS goes high or

a falling edge on LIN bus had been detected.

POR

VREN OFF

RX OFF

TX OFF

Ready Mode

VREN ON

RX ON

TX OFF

VBAT > 5.5V

Falling Edge

on LIN or CS = 1

TOFF Mode

VREN ON

RX ON

TX OFF

Power-Down

Mode

VREN OFF

RX OFF

TX OFF

CS = 1 and TXD = 1

and No Fault

Fault

(Thermal or Timer)

CS = 0

Operation

Mode

VREN ON

RX ON

TX ON

CS = 1 and TXD = 0*

Note: * TXD = 0 before raising CS to ‘1’.

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FIGURE 3: Switching Timing Diagram for the Forced Power-Down Mode Sequence.

TXD

VREN

Ready

Mode Transmitt er OFF

Mode

Power Down

Mode after Master

Sleep instruction

Power Down

Mode

tTx2CS >= 100ns tC Sa ctive >= 100µs

TXD to 0

forced

externally

TXD state depending

on how the Sl av e

Microcontroller is

powered

LBUS

State

LIN b us

disconnected

TB3067

FIGURE 4: PIC® Microcontroller Code Example for Forced Power-Down Mode.

/* design specific */

#define TXPINLATCbits.LATC6

#define CSPINLATCbits.LATC0

/* please refer to data sheet regarding maximum values */

#define WaitTimeTx2CS() Nop(); Nop();Nop(); Nop();

#define WaitTimeCSactive() unsigned char dly; dly = 55; while(--dly);

/**********************************************************************/

void ForcedSleepMCP200x(void)

{

/* set LATregister of corresponding IOpin for TX -> 0 */

TXPIN = 0;

/* depending if TXEN in TXSTA register allows the use of the

/* corresponding IOpin for TX as a normal IO when TXEN = 0 then set */

/* TXPIN = 0 otherwise reset the whole UART module. Please refer to */

/* controller specific data sheet and review the UART section */

#if defined (TXEN_FREE_IO) /* TX also usable as IO */

TXEN = 0;

#else

RCSTA = 0;

#endif

WaitTimeTx2CS(); /* refer to data sheet */

CSPIN = 1; /* CS = 1 -> transceiver activated but TX = 0 */

WaitTimeCSactive(); /* refer to data sheet */

CSPIN = 0; /* CS = 0 -> transceiver in SLEEP mode */

}

/**********************************************************************/

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