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L4969

1.3

CAN Transceiver

– Supports double wire unshielded busses

– Baud rate up to 125KBaud

– Short circuit protection (battery, ground, wires shorted)

– Single wire operation possible (automatic switching to single wire upon bus failures)

– Bus not loaded in case of unpowered transceiver

The CAN transceiver stage is able to transfer serial data on two independent communication wires either def-

erentially (normal operation) or in case of a single wire fault on the remaining line. The physical bitcoding is done

using dominant (transmitter active) and overwritable recessive states. Too long dominant phases are detected

internally and further transmission is automatically disabled (malfunction of protocol unit does not affect com-

munication on the bus, "fail-safe" - mechanism). For low current consumption during bus inactivity a sleep mode

is available. The operating mode can be entered from the sleep mode either by local wake up (

tection of a dominant bit on the CAN-bus (external wake up).

Ten different errors on the physical buslines can be distinguished:

1.3.1 Detectable Physical Busline Failures

Not all of the 10 different errors lead to a breakdown of the whole communication.

So the errors can be categorized into 'negligible', 'problematic' and 'severe':

N

Type of Errors

Conditions

Errors caused by damage of the datalines or isolation

I

CANH wire interrupted (tied to Ground or termination)

Edgecount difference > 3

II

CANL wire interrupted (floating or tied termination)

Edgecount difference > 3

III

V(CANH) > 7.2V after 32us

IV

CANL short circuit to GND (permanently dominant)

V(CANL) < 3.1V & V(CANH)-V(CANL)

< -3.25V after 1.3ms

V

CANH short circuit to GND (permanently recessive)

Edgecount difference > 3

VI

V(CANL) > 7.2V after 32us

VII

CANL shorted to CANH

V(CANH) - V(CANL) < -3.25V after

1.3ms

Errors caused by misbehavior of transceiver stage

VIII

CANH short circuit to VDD (permanently dominant)

V(CANH) > 1.8V & V(CANH) -

V(CANL) < -3.25V after 2.5ms

IX

CANL short circuit to VDD (permanently recessive)

Edgecount difference > 3

Errors caused by defective protocol unit

X

CANH, CANL driven dominant for more than 1.3ms