Philips PCA82C252, TJA1053, TJA1054, TJA1054A Technical data

Philips Semiconductors	Systems Laboratory Hamburg, Germany
APPLICATION HINTS	Fault-tolerant CAN Transceiver

Application Hints

Fault-tolerant CAN Transceiver

PCA82C252 / TJA1053 / TJA1054 / TJA1054A

Version 3.1

Date : 23rd of November 2001

Application Hints FTCAN 3_1.PDF

Philips

Semiconductors

Philips Semiconductors	Systems Laboratory Hamburg, Germany
APPLICATION HINTS	Fault-tolerant CAN Transceiver

Revision History

Changes Version 1.0 -> 2.0 :

1.Chapter 3, calculation examples for PCA82C252 and TJA1053 added, new aspects

2.Chapter 4, calculation hints for termination resistors added, new aspects

Changes Version 2.0 -> 2.1 :

1.Chapter 6 added

2.Chapter 7 added

3.Chapter 8 added

Changes Version 2.1 -> 2.2 :

1.Chapter 5, clarification that external ESD diodes are optional for further improvements

2.Chapter 8 added, Software design hints ( previous chapter 8 re-numbered to chapter 9 )

3.Chapter 9, FAQ 9.6, No communication at CANH to VCC short circuit

Changes Version 2.2 -> 3.0 :

1.Foreword added

2.Chapter 2 added, Upgrading Note TJA1053 -> TJA1054

3.Chapter 3 added, Mode Control of the TJA1054

4.Chapter 5, formula 11 corrected, calculation example updated

5.Chapter 10, Software design hints dealing with the pin ERR added

Changes Version 3.0 -> 3.1 :

1.Editorial changes

2.Chapter 8, series resistor at pin WAKE, more details

3.Chapter 9 added, series resistor at pins TXD

Foreword

In this document, application related information for the various fault-tolerant transceiver implementations from Philips Semiconductors is collected. The different transceivers are a result of a continuous improvement of the fault-tolerant and system performance.

The first available product in the market was the PCA82C252, followed by the TJA1053 and later on by the TJA1054. In the mean time even the TJA1054 has become improved with respect to ESD capabilities. The so-called TJA1054A behaves identical to the TJA1054 but offers a higher ESD robustness on the bus-related pins. Thus wherever the TJA1054 is mentioned within this document it could also be read as TJA1054A, except in case a certain transceiver type is mentioned explicitly.

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Philips Semiconductors	Systems Laboratory Hamburg, Germany
APPLICATION HINTS	Fault-tolerant CAN Transceiver
Table of Contents :
1. Comparison PCA82C252 / TJA1053 / TJA1054 / TJA1054A.........................................................		6
1.1. System parameters........................................................................................................................		6
1.2. Device parameters.........................................................................................................................		6
2. Upgrading a TJA1053 Design with the TJA1054...........................................................................		7
2.1. Overview ........................................................................................................................................		7
2.2. Hardware Issues ............................................................................................................................		7
2.2.1. External Components..............................................................................................................		7
2.2.2. Wake-up sensitivity at pin WAKE............................................................................................		8
2.2.3. Current consumption ...............................................................................................................		8
2.2.4. Operating Voltage Range........................................................................................................		8
2.3. Software Issues .............................................................................................................................		9
2.3.1. Error signalling via pin ERR ....................................................................................................		9
2.3.1.1. Software polls pin ERR.....................................................................................................		9
2.3.1.2. Software reads pin ERR during CAN interrupt service only.............................................		9
2.3.2. VCC Standby / PWON Standby ..............................................................................................		9
2.3.3. First Battery Connection, behaviour of pin INH.......................................................................		9
2.3.4. Goto-Sleep / Wake-up Priority ................................................................................................		9
2.3.5. Other issues ..........................................................................................................................		10
2.4. Interoperability : Mixed Systems with TJA1053 and TJA1054 ....................................................		10
2.4.1. Overview ...............................................................................................................................		10
2.4.2. Hardware Interoperability Investigations ...............................................................................		10
2.4.3. Results of Hardware Interoperability Investigation................................................................		11
1.5. Conclusion ...................................................................................................................................		11
1.6. Migration Checklist.......................................................................................................................		12
3. Mode Control with the TJA1054....................................................................................................		13
3.1. Overview ......................................................................................................................................		13
3.2. Operating Modes .........................................................................................................................		14
3.2.1. Normal Mode.........................................................................................................................		14
3.2.2. Goto Sleep ............................................................................................................................		15
3.2.3. Stby Sleep .............................................................................................................................		15
3.2.4. PWON Stby ...........................................................................................................................		15
3.3. System Wake-up..........................................................................................................................		15
3.3.1. Local wake-up .......................................................................................................................		15
3.3.2. Remote wake-up ...................................................................................................................		15
3.3.3. Mode change.........................................................................................................................		15
3.4. State diagrams.............................................................................................................................		16
3.4.1. PWON Flag ...........................................................................................................................		16
3.4.2. Pin INH ..................................................................................................................................		16
3.4.3. Wake-up Flag ........................................................................................................................		16
3.4.4. Pin RXD.................................................................................................................................		16
3.4.5. Pin ERR.................................................................................................................................		17
4. Vcc Supply and Recommended Bypass Capacitance ...............................................................		18
4.1. List of used Abbreviations............................................................................................................		18
1.2. Summary......................................................................................................................................		19
1.3. Average Supply Current at Absence of Bus Short-Circuit Conditions.........................................		20
1.3.1. Maximum dominant supply current (without bus wiring faults) .............................................		20
1.3.1.1. Example calculation........................................................................................................		20
1.3.2. Thermal considerations (without bus wiring faults) ...............................................................		20
1.3.2.1. Example calculation........................................................................................................		20
1.4. Average Supply Current at	Presence of a Short-Circuit of one Bus Wire ..................................	21
1.4.1. Maximum dominant supply current (with CANH shorted to GND)........................................		21
1.4.1.1. Example calculation........................................................................................................		21

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Philips Semiconductors	Systems Laboratory Hamburg, Germany
APPLICATION HINTS	Fault-tolerant CAN Transceiver
1.4.2. Thermal considerations (with CANH shorted to GND)..........................................................		21
1.4.2.1. Example calculation........................................................................................................		21
1.4.3. Vcc extra supply current in single fault condition ..................................................................		22
1.1.1.1. Example calculation........................................................................................................		22
1.5. Worst Case Max Vcc Supply at Presence of a Dual Short Circuit...............................................		23
1.5.1. Max Vcc supply current in worst case dual fault condition....................................................		23
1.5.1.1. Example calculation........................................................................................................		23
1.5.2. Vcc extra supply current in dual fault condition.....................................................................		24
1.1.1.1. Example calculation........................................................................................................		24
1.6. Calculation of worst-case bypass capacitor.................................................................................		24
1.1.1. Example calculation, separate supplied transceiver @ 83,33kBit/s .....................................		25
1.1.2. Example calculation, shared supply......................................................................................		25
5. Bus Termination and EMC issues ................................................................................................		26
5.1. How to dimension the Bus Termination Resistor values, some basic rules ................................		26
5.1.1. Variable System Size, Optional Nodes .................................................................................		26
5.1.1.1. Example calculation, Variable System Size ...................................................................		27
5.2. Tolerances of Bus Termination Resistors, EMC Considerations.................................................		27
5.3. Output Current and Power Dissipation of Bus Termination Resistors RT....................................		28
5.3.1. Summary ...............................................................................................................................		28
5.3.2. Average power dissipation, no bus failures ..........................................................................		28
5.3.2.1. Example calculation, average power dissipation............................................................		28
5.3.3. Maximum continuous power dissipation (single bus failure).................................................		28
5.3.3.1. Example calculation, maximum continuous power dissipation ......................................		28
5.3.4. Maximum peak power dissipation (single bus failure) ..........................................................		29
5.3.4.1. Example calculation, maximum peak power dissipation ................................................		29
6. ESD Protection ...............................................................................................................................		30
6.1. Improved ESD capability of TJA1054A........................................................................................		30
6.2. Optional external ESD Improvement ...........................................................................................		30
7. Series Resistor at Pin BAT............................................................................................................		31
8. Series Resistor at Pin WAKE ........................................................................................................		32
1.1. Parameters defining the range of RS ...........................................................................................		32
1.2. Calculating the limits of RS...........................................................................................................		33
1.3. Example calculation .....................................................................................................................		33
9. Series Resistor at Pin TXD ............................................................................................................		34
9.1. Parameters defining the range of RTXD ........................................................................................		34
9.2. Calculating the Limits of RTXD ......................................................................................................		34
9.3. Example calculation .....................................................................................................................		34
10. Hardware Design Checklist...........................................................................................................		35
11. Software Design Hints ...................................................................................................................		36
11.1. System Sleep Procedure ...........................................................................................................		36
11.2. Using the ERR output for failure diagnosis................................................................................		37
11.2.1. ERR signal at open bus wires .............................................................................................		37
11.2.1.1. Behaviour using PCA82C252 / TJA1053 .....................................................................		37
11.2.1.2. Behaviour using TJA1054 ............................................................................................		38
11.2.2. ERR signal while CANH shorted to GND or CANL shorted to VCC ...................................		38
11.2.3. ERR signal while other short circuit conditions ...................................................................		38
11.3. Using ERR for Reading out the PWON Flag .............................................................................		39

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Philips Semiconductors	Systems Laboratory Hamburg, Germany
APPLICATION HINTS	Fault-tolerant CAN Transceiver
12. Frequently Asked Questions ........................................................................................................		40
12.1. The transceiver does not enter the Sleep Mode........................................................................		40
12.2. System operates in Single Wire Mode all time ..........................................................................		40
12.3. System does not wake-up, even if there is bus activity .............................................................		40
12.4. Transceiver is damaged when external tools are connected ....................................................		41
12.5. CAN tool cannot communicate with certain application.............................................................		41
12.6. No communication at CANH to VCC short circuit......................................................................		41

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Philips Semiconductors	Systems Laboratory Hamburg, Germany
APPLICATION HINTS	Fault-tolerant CAN Transceiver

1. Comparison PCA82C252 / TJA1053 / TJA1054 / TJA1054A

1.1. System parameters

Key	PCA82C252	TJA1053	TJA1054
System size	10 – 15 nodes 1) 2)	10 – 15 nodes 2)	> 32 nodes
Speed	20 - <125 kbps 3)	20 – 125 kbps	40 – 125 kbps
Emission	+	+	++
Immunity	+	+	++
TxD dominant monitoring	no	yes	yes
Extended bus failure	no	no	yes
management
(CANH to Vcc)
Resolved problem of	no	yes	yes
arbitration across open
failures

1)The limit is given by the performance during CANH to ground failures, which very much depends on the size and type of cable used.

2)The limit is given by the wake-up capability during CANH to ground failures, which very much depends on the values of the distributed terminations across the network. Therefore, exact figures of system size cannot be given.

3)With CANH to VBAT failures the delay of the dominant edge is increased. The maximum speed strongly depends on the inductance of the cable used.

1.2. Device parameters

Key	PCA82C252		TJA1053		TJA1054		TJA1054A
Current consumption in	6 mA	(rec)	6 mA	(rec)	7 mA	(rec)	7 mA	(rec)
Normal Mode (ICC)	29 mA	(dom)	29 mA	(dom)	17 mA	(dom)	17 mA	(dom)
Current consumption in	70 uA		70 uA		30 uA		30 uA
Standby Modes (IBAT +
ICC)
Minimum operating	6V		6V		5V		5V
voltage
Prevention of VBAT	no		no		yes		yes
reverse current 1)
WAKE sensitivity	negative edge		negative edge		both edges		both edges
Vcc Standby mode	yes		yes		no		no
ERR reporting of open	during frame only		during frame only		during frame and		during frame and
failures					inter frame space		inter frame space
ESD Protection pins	2kV Human Body		2kV Human Body		2kV Human Body		4kV Human Body
RTH / RTL / CANH /	200V Machine M.		200V Machine M.		200V Machine M.		300V Machine M.
CANL

1)In case a module looses its battery connection, a reverse power supply of this module via the CAN bus lines is prevented. For the PCA82C252 and the TJA1053 an external diode at the battery pin of the transceiver is required. This diode is required additionally to the control unit’s polarity protection diode typically implemented at the battery connector of the entire module.

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Philips Semiconductors	Systems Laboratory Hamburg, Germany
APPLICATION HINTS	Fault-tolerant CAN Transceiver

2. Upgrading a TJA1053 Design with the TJA1054

2.1. Overview

The TJA1054 is a fault-tolerant CAN transceiver suitable for networks including up to 32 nodes and is the compatible successor of the well-known TJA1053. Compared with the TJA1053, the TJA1054 provides several enhanced features:

•Extremely reduced electro-magnetic emission (EME)

•Very good electro-magnetic immunity (EMI)

•Enhanced bus failure management (short circuits to 5V are tolerated)

•Improved error signalling

•Improved behaviour during “Loss of Power” situations

The TJA1054 is designed to be downward compatible to the TJA1053 and can be used in most of the existing TJA1053 applications without any changes in hardware and software. Nevertheless, due to the enhanced functionality there are some points to be considered if the TJA1053 is replaced by the TJA1054.

The following chapters discuss all hardware and software issues in detail in order to allow a smooth migration from the TJA1053 to the TJA1054.

Special attention is paid to interoperability issues giving the confidence that both devices can be used simultaneously within one network. Validation showed that a “step-by-step” introduction of the TJA1054 into an existing TJA1053 system can be made without risk.

2.2. Hardware Issues

2.2.1. External Components

When the TJA1053 is replaced by a TJA1054, two external hardware components may be removed (see also figure 1) :

•Reverse current protection diode at pin BAT

•Pulse lengthening capacitor at pin ERR

The extra diode for the TJA1053 is needed to suppress a reverse power supply of the control unit if the battery connection of the entire unit was lost. For the TJA1053, a current flow from the CANL bus line backward to the pin BAT of the transceiver was possible if the transceiver was not powered. In some applications, this reverse current was high enough to supply the microcontroller unintentionally. The TJA1054 is internally protected against such reverse currents making the diode superfluous.

Reading the pin ERR during the normal CAN interrupt service routine was not possible for the TJA1053 in case of “open failures” on the bus lines. Here, the so-called “acknowledge bit” of any valid CAN message cleared an already detected “open failure” at the pin ERR. Therefore, an external lengthening capacitor was required for the TJA1053 in order to keep the detected failure signal valid until the interrupt service routine was executed by the host uC.

The TJA1054 does not require this extra lengthening capacitor since the pin ERR now internally keeps the failure signal active. ( see also 11.2.1. )

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Philips Semiconductors				Systems Laboratory Hamburg, Germany
APPLICATION HINTS				Fault-tolerant CAN Transceiver
				BAT
				5V
			**	100n
	optional *
VCC	TXD	TXD	VCC
	RXD	RXD	INH
uC

+I/O STB

	CAN		EN
	I/O
	I/O		ERR	VBAT
					1k - 2k
	GND	470n
			PCA82C252		10n
				or
					<180k
				TJA1053
			CANH	or
		<150pF		TJA1054
	RTH***
			RTH	WAKE
					> 1k8
			RTL
	RTL***				WAKE-UP
			CANL
		<150pF		GND
	CAN
	bus

*For further EMC optimization a series resistor could be applied in case the bus timing parameters allow this additional delay caused by the additional R/C time constant.

**Size of capacitor depends on regulator.

***Size of termination resistors depends on system size. The overall system termination should be about 100 Ohms per CAN line.

Figure 1 : Typical application circuitry using the TJA1053 and the TJA1054

2.2.2. Wake-up sensitivity at pin WAKE

The wake-up input of the TJA1054 is sensitive on both edges, whereas the TJA1053 was sensitive on the falling edge only. This has typically no impact on the application since such external wake-up events are usually pulses including both edges.

Another improvement of the TJA1054 is that wake-up events have higher priority than the goto-sleep command. Systems using the TJA1053 may lose such a wake-up event. Consequently, a TJA1053 node may keep sleeping without starting the voltage regulator although a wake-up request has been driven to the pin WAKE. The TJA1054 will now recognise any wake-up event independently from the current command setting of the host CPU.

2.2.3. Current consumption

The total current consumption of the TJA1054 is reduced compared to the TJA1053, especially during low-power modes. The slightly increased short circuit current of the CANH bus driver within the TJA1054 is compensated by its reduced normal mode supply current during dominant bus states. Thus, there is no impact to the applications power supply concept. But introduction of the TJA1054 provides a much lower sleep current per control unit now compared with the TJA1053.

Condition		TJA1053		TJA1054
Current consumption in Normal Mode, ICC	6 mA	recessive	7 mA	recessive
	29mA dominant		17mA dominant
Current consumption in Low-power Modes, IBAT + ICC	70uA		30uA

2.2.4. Operating Voltage Range

In order to increase the system performance during low battery conditions, the TJA1054 now allows operation down to 5V at the pin BAT, whereas the TJA1053 required at least 6V.

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Philips Semiconductors	Systems Laboratory Hamburg, Germany
APPLICATION HINTS	Fault-tolerant CAN Transceiver

2.3. Software Issues

2.3.1. Error signalling via pin ERR

As already mentioned before, the behaviour of the error signalling at the pin ERR is improved within the TJA1054. This allows removing the external lengthening capacitor needed for the TJA1053 (see also 2.1). This new behaviour of the TJA1054 may have an impact on application software if the TJA1053 was used without external lengthening capacitor. Two scenarios are possible:

2.3.1.1. Software polls pin ERR

Application software polling the pin ERR will see fewer transitions if the TJA1053 is replaced by the TJA1054. Especially during “open failures” on the bus lines, the software load caused by ERR events is reduced if the TJA1054 is used.

2.3.1.2.Software reads pin ERR during CAN interrupt service only

Here, the “open failures” are now detected and signalled by the TJA1054 as desired, whereas the TJA1053 has signalled no problem. Thus, a simple migration to the TJA1054 automatically improves a software driven diagnosis function.

2.3.2. VCC Standby / PWON Standby

The VCC Standby Mode known from the TJA1053 is replaced by the so-called PWON Standby Mode in the TJA1054 (STB = 1; EN = 0). There is no change in functionality between both transceivers except for the CANL biasing level. The TJA1053 drives 5V to CANL through pin RTL and the termination resistor, while the TJA1054 now drives 12V to CANL using the same path. This has no impact on the overall system performance if both transceivers are mixed in one network. Software is not influenced since both transceivers provide the same status information to the microcontroller via ERR and RXD.

2.3.3. First Battery Connection, behaviour of pin INH

The TJA1053 allows to be set into Sleep Mode (INH floating) directly after first battery connection by driving the goto-sleep command to the control pins STB and EN (“01”). The TJA1054 needs to be set into Normal Mode before accepting the first goto-sleep command after first connection of the battery supply. After setting Normal Mode both devices behave identical concerning this item.

An internal power-on reset signal within the TJA1054 makes sure that the transceiver is reset successfully after power-up and the INH output is safely set to battery level. This internal reset signal is cleared whenever the Normal Mode is entered once. There are no special timing requirements to clear the internal reset signal thus software just has to set the Normal Mode via STB and EN followed by any other control code. Within most of the existing applications this is already implemented inside of the systems cold-start routines.

2.3.4. Goto-Sleep / Wake-up Priority

The pin INH of the TJA1053 does ignore wake-up events in case these wake-up events are present while the goto-sleep command is continuously driven to the transceiver via pins STB and EN (STB = 0 / EN = 1). After the goto-sleep filter time ( see data sheets TJA1054/TJA1054A : “reaction time of goto sleep command” ) the INH flip-flop is continuously cleared thus setting the pin INH to a floating condition. Wake-up events are forwarded to INH first with releasing the goto-sleep command. Thus a systems voltage regulator connected to INH will become disabled even if there is a pending wake-up request. Nevertheless RXD and ERR will signal the wake-up event with a LOW output level independently from the pending goto-sleep command.

For the TJA1054 this behaviour is improved and no wake-up event is lost with respect to the pin INH. Within the TJA1054 the wake-up events have a higher priority than the goto-sleep command. Thus any wake-up event will reset INH to a HIGH output level independently from the goto-sleep command. RXD and ERR will reflect the wake-up condition with a LOW output level as known from the TJA1053. From software point of view it is highly recommended for both transceivers monitoring the pins RXD and/or ERR whenever the goto-sleep command was executed in order to detect a wake-up event

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APPLICATION HINTS	Fault-tolerant CAN Transceiver

while the system should fall into sleep mode. INH might keep HIGH or become HIGH again caused by a wake-up event before the supply of the uC was successfully disabled. ( see also 11.1. )

2.3.5. Other issues

Experiences with different software drivers have shown the advantage to implement a kind of CAN communication monitoring in software, expecting CAN bus events in certain time frames. At least a reception of messages or successful transmissions should appear in order to get confidence, that the CAN bus is still operating properly. This is especially important for recovery from dual bus failure situations towards single bus failure situations.

Due to the automatic transmit message repetition mechanism of a CAN protocol engine it might happen that a node retransmits a message forever in case there is no acknowledge received from the bus. This continuously transmitting node might lock the bus system and thus prevents other nodes to recover from a dual bus failure situation towards a single bus failure situation.

Therefore, whenever there is no response from the CAN bus within a reasonable time, pending transmission requests should be aborted in software. This will increase the system availability during certain bus failure conditions, which require single wire operation.

2.4. Interoperability : Mixed Systems with TJA1053 and TJA1054

2.4.1. Overview

During development of the TJA1054 special attention was paid to interoperability issues in order to allow a smooth migration of existing applications by simple replacement of the TJA1053. Particularly, the enhancements of the bus failure management (5V short circuits) have been included very carefully into the existing circuitry to avoid system hang-ups, if both transceivers are mixed in one system.

The TJA1054 is designed to replace the TJA1053 within running car series production without interoperability risk.

Interoperability of both devices has been proved in system simulation as well as in hardware investigation.

The key results of these investigations are :

• A pure TJA1054 network solves the known weaknesses of a TJA1053 system ( wake-up of big networks with failure HxGND, short circuits to 5V .... )

•A mixed system of TJA1053 and TJA1054 has at least the same performance as the pure TJA1053 system; in some aspects the growing presence of TJA1054 nodes in the network even improves the overall system performance

•Taking into consideration the issues described in the previous chapters, mixed systems of both transceiver are possible at any ratio without restrictions

2.4.2. Hardware Interoperability Investigations

In order to investigate interoperability issues of the transceiver, a network with 25 nodes was set up and investigated in detail. A typical topology including star points was chosen according to real automotive applications. This topology includes cable stubs with more than 5 meters and more than 55 meters overall cable length.

Worst case scenarios were analysed including weak bus failure conditions, double failures, ground shifts and power supply drops. Especially, operating mode changes (Normal Mode / Standby / Sleep) were performed simultaneously with bus failure situations.

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APPLICATION HINTS	Fault-tolerant CAN Transceiver

2.4.3. Results of Hardware Interoperability Investigation

The following table gives an overview about the mixed system investigations using the TJA1053 together with the TJA1054 in different mixing ratios. An assessment is made compared with a pure TJA1053 system with same topology.

Bus Failure	Communicationwith Ground1.5V)Shift(+/-	Communicationat LowVoltagesBattery	ModeChangesWakeup-/ combinedwithBus ConditionsFailure	Communicationlocalwith TerminationLoss of
CommunicationStandard ( incl.resistivefailures)

0	none	9	9	9	9	9
1	H //	9	9	9	-	-
2	L //	9	9	9	9	9
3	HxBAT	-	9	9	9	9
3a	HxVCC	-	-	-	-	-
4	LxGND	9	-	9	9	9
5	HxGND	9	9	9	-	9
6	LxBAT	9	-	9	9	9
6a	LxVCC	9	9	9	-	9
7	HxL	9	9	9	9	9

Key :

( - ) mixed system behaves better than a pure TJA1053 system ( 9 ) mixed system behaves equal to a pure TJA1053 system

( ' ) mixed system behaves worse than a pure TJA1053 system

2.5. Conclusion

Both transceivers, TJA1053 and TJA1054, are interoperable and can be used simultaneously within the same network. This allows migrating gradually from TJA1053 to TJA1054 in running car mass production.

Due to new features introduced with the TJA1054, existing TJA1053 applications need to be reviewed according to the comments within this report before replacing the transceiver.

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	Philips Semiconductors		Systems Laboratory Hamburg, Germany
	APPLICATION HINTS		Fault-tolerant CAN Transceiver
	2.6. Migration Checklist
	Item	TJA1053	TJA1054	Comment
	Diode @ pin BAT	needed	can be removed	no reverse power supplying by
				TJA1054
	Capacitor @ pin ERR	depends on	can be removed	function is integrated into the
		software		TJA1054
	Sensitivity of pin WAKE	falling edge only	both edges	check behaviour of system wake-up
				via pin WAKE
	Goto-sleep command	always possible	possible only after	Internal power-on signal has to be
	after first battery		Normal Mode was	cleared by setting the TJA1054 into
	connection		entered once	Normal Mode after first battery
				connection
	Goto-sleep command,	INH becomes	INH keeps HIGH if	It is recommended to monitor pin
	priority of wake-up event	floating the time	there is a wake-up	RXD and/or pin ERR after goto-
		goto-sleep is driven	coming during goto-	sleep in order to detect a wake-up
		even if there is a	sleep is driven	event during the transition into
		wake-up coming		Sleep Mode.

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APPLICATION HINTS	Fault-tolerant CAN Transceiver

3. Mode Control with the TJA1054

3.1. Overview

The fault tolerant CAN transceiver TJA1054 provides an integrated functionality controlling an external voltage regulator in order to design low power CAN bus systems with remote and local wake-up capabilities. A dedicated INH pin allows disabling the entire power supply of a control unit, thus reducing the overall system power consumption to a minimum. The transceiver is the only supplied component during such a low-power state.

Following figure shows an application example using the TJA1054.

	BAT
	5V
**	100n

optional *

VCC TXD						TXD	VCC
RXD						RXD	INH

uC

+I/O STB

CAN	EN
I/O
I/O	VBAT
	ERR
GND	1k - 2k

10n

TJA1054

CANH

<150pF

RTH***

WAKE

RTH

> 1k8

RTL

RTL***

CANL

<150pF

GND

CAN bus

<180k

WAKE-UP

*For further EMC optimization a series resistor could be applied in case the bus timing parameters allow this additional delay caused by the additional R/C time constant.

**Size of capacitor depends on regulator.

***Size of termination resistors depends on system size. The overall system termination should be about 100 Ohms per CAN line.

Figure 2 : Typical application of the TJA1054

As shown within Figure 2 the transceiver is powered directly from the battery supply via the pin BAT. This allows disabling the VCC supply entirely during time phases, the CAN bus is not required by the system. Therefore two control pins STB and EN coming from the host microcontroller are used to control the actual mode of operation like normal communication or low-power operation.

For wake-up purposes a battery-related WAKE pin is provided.

In addition to bus failure information and the CAN received bit stream, the pins ERR and RXD are used to signal wake-up requests towards the application controller.

Application Hints V3.1

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