33389 datasheet(20/49 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33389

FUNCTIONAL DEVICE OPERATION

speed applications up to 125 kBit/s in passenger cars. It

provides differential transmission capability, but will switch in

error condition to single wire transmitter and/or receiver.

The rise and fall slopes are limited to reduce radio

frequency interference (RFI). This provides use of an

unshielded twisted pair or a parallel pair of wires for the bus.

It supports transmission capability on either bus wire if one of

the bus wire is corrupted. The logic failure detection

automatically selects a suitable transmission mode.

In a normal operation (no wiring failures), the differential

bus state is the output to RX. The differential receiver inputs

are connected to CANH and CANL through integrated filters.

The filtered inputs signals are also used for the single wire

receivers. The CANH and CANL receivers have threshold

voltages, assuring maximum noise margin in single wire

modes. In the RX Only mode, the transmitter is disabled;

however, the receive part of the transceiver remains active. In

this mode, RX reports bus and TX activity (RX = TX or Bus

dominant). Failure detection and management is the same as

the Bus Normal mode.

Failure Detector

The failure detector is active in RXTX and RX Only

operation modes. The detector recognizes the following

single bus failures and switches to an appropriate mode.

1. CANH wire interrupted

2. CANL wire interrupted or shorted to 5.0 V

3. CANH short-circuit to battery

4. CANL short-circuit to ground

5. CANH short-circuit to ground

6. CANL short-circuit to battery

7. CANL mutually shorted to CANH

8. CANH to V2 (5.0 V)

Note: Shorts-circuit failures are detected for 0 to 50

Ω shorts.

The differential receiver (CANH-CANL) threshold is set at

-2.8 V, this assures a proper reception in the normal

operating modes. In case of failures 1, 2, and 5 the on-going

message is not destroyed due to noise margin.

Failures 3 and 6 are detected by comparators respectively

connected to CANH and CANL. If the comparator threshold

is exceeded for a certain time (TAC3D, TAC6D), the reception

is switched to single wire mode. This time is required to avoid

false triggering by external RF fields. Recovery from these

failures is detected automatically after a certain (TAC3R,

TAC6R) time-out (filtering).

Failures 4 and 7 initially result in a permanent dominant

level at RX. After a time-out, the CANL driver and the RTL

pins are switched OFF. Only a weak pull-up at CANL

remains. Reception continues by switching to Single Wire

mode through CANH. When Failures 4 or 7 are removed, the

recessive bus levels are restored. If the differential voltage

remains below the recessive threshold for a certain (TAC478R)

time, reception and transmission switch back to the

Differential mode.

If any of the eight wiring failure occurs, a flag is set in the

TESRH and TESRL Status registers. Eight different types of

errors are distinguished out of these eight errors. They are

separately stored in these register. Please refer to the

Tables 35 and 36. A maskable interrupt is sent to the

microcontroller. On error recovery, the corresponding flag is reset

after read-out operation.

During all single wire transmissions, the EMC performance

(both immunity and emission) is worse than in the Differential

mode. Integrated receiver filters suppress any high frequency

noise induced into the bus wires. The cut-off frequency of

these filters is a compromise between propagation delay and

high frequency suppression. In the Single Wire mode, low

frequency noise can not be distinguished from the expected

signal.

In the event of a permanent dominant TX state (for more

than 2.0 ms) the output drivers are disabled. That assures the

operation of the complete system in case of a permanent

dominant TX state of one control unit. The CAN interface of a

defective ECU, which has TX permanently low, will

automatically be set to the receive only mode and therefore

will not lock the complete CAN bus.

Protection

A current limiting circuit protects the transmitter output

stages against short-circuit to positive and negative battery

voltage. If the junction temperature exceeds a maximum

value, the transmitter output stages are disabled. Because

the transmitter is responsible for a part of the power

dissipation, this results in a reduced power dissipation

resulting in a lower chip temperature. All other parts of the

transceiver will remain operating. The CANH and CANL

inputs are protected against electrical transients, and may

occur in an automotive environment.

Thermal Management

The 33389 is proposed in two different packages:

1. HSOP-20 for high power applications

2. SO28WB with eight pins to the lead frame for medium

power applications

HSOP20 Package

For such a package, the heat flow is mainly vertical and

each heat source (dissipating element) can be seen as an

independent thermal resistance to the Heatsink. The thermal

network can be roughly depicted in Figure 6.

33389 Datasheet(PDF) 20 Page - Freescale Semiconductor, Inc

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