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TJA1041A

High speed CAN transceiver

Philips Electronics 

Philips Semiconductors

High speed CAN transceiver

Product specification

TJA1041A

The tdom(TXD) timer defines the minimum possible bit rate

of 40 kbit/s. The transmitter remains disabled until the

local failure flag is cleared.

junction temperature exceeds the shutdown junction

temperature Tj(sd). The transmitter remains disabled until

the local failure flag is cleared.

RXD RECESSIVE CLAMPING DETECTION

An RXD pin clamped to HIGH level will prevent the

controller connected to this pin from recognizing a bus

dominant state. So the controller can start messages at

any time, which is likely to disturb all bus communication.

RXD recessive clamping detection prevents this effect by

disabling the transmitter when the bus is in dominant state

without RXD reflecting this. The transmitter remains

disabled until the local failure flag is cleared.

TXD-TO-RXD SHORT-CIRCUIT DETECTION

A short-circuit between pins RXD and TXD would keep the

bus in a permanent dominant state once the bus is driven

dominant, because the low-side driver of RXD is typically

stronger than the high-side driver of the controller

connected to TXD. The TXD-to-RXD short-circuit

detection prevents such a network lock-up by disabling the

transmitter. The transmitter remains disabled until the local

failure flag is cleared.

BUS DOMINANT CLAMPING DETECTION

A CAN bus short circuit (to VBAT, VCC or GND) or a failure

in one of the other network nodes could result in a

differential voltage on the bus high enough to represent a

bus dominant state. Because a node will not start

transmission if the bus is dominant, the normal bus failure

detection will not detect this failure, but the bus dominant

clamping detection will. The local failure flag is set if the

dominant state on the bus persists for longer than tdom(bus).

By checking this flag, the controller can determine if a

clamped bus is blocking network communication. There is

no need to disable the transmitter. Note that the local

failure flag does not retain a bus dominant clamping

failure, and is released as soon as the bus returns to

recessive state.

OVER-TEMPERATURE DETECTION

To protect the output drivers of the transceiver against

overheating, the transmitter will be disabled if the virtual

Recessive bus voltage stabilization

In recessive state the output impedance of transceivers is

relatively high. In a partially powered network (supply

voltage is off in some of the nodes) any deactivated

transceiver with a significant leakage current is likely to

load the recessive bus to ground. This will cause a

common-mode voltage step each time transmission starts,

resulting in increased ElectroMagnetic Emission (EME).

Using pin SPLIT of the TJA1041A in combination with split

termination (see Fig.5) will reduce this step effect. In

normal mode and pwon/listen-only mode pin SPLIT

provides a stabilized 0.5VCC DC voltage. In standby mode,

go-to-sleep command mode and sleep mode pin SPLIT is

set floating.

I/O level adapter

The TJA1041A is equipped with a built-in I/O-level

adapter. By using the supply voltage of the controller (to be

supplied at pin VI/O) the level adapter ratio-metrically

scales the I/O-levels of the transceiver. For pins TXD, STB

and EN the digital input threshold level is adjusted, and for

pins RXD and ERR the HIGH-level output voltage is

adjusted. This allows the transceiver to be directly

interfaced with controllers on supply voltages between

2.8 V and 5.25 V, without the need for glue logic.

Pin WAKE

Pin WAKE of the TJA1041A allows local wake-up

triggering by a LOW to HIGH state change as well as a

HIGH to LOW state change. This gives maximum flexibility

when designing a local wake-up circuit. To keep current

consumption at a minimum, after a twake delay the internal

bias voltage of pin WAKE will follow the logic state of this

pin. A HIGH level on pin WAKE is followed by an internal

pull-up to VBAT. A LOW level on pin WAKE is followed by

an internal pull-down towards GND. To ensure EMI

performance in applications not using local wake-up it is

recommended to connect pin WAKE to pin VBAT or to pin

GND.

2004 Feb 20

10

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