33394 datasheet(23/44 Pages) FREESCALE

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33394

MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA

The Wake–up function can be disabled through SPI by setting

the WKUP bit to 0.

The CAN transceiver of the 33394 is designed for

communications speeds up to 1.0 Mbps. The use of a

common mode choke may be required in some applications.

When the 33394 CAN transceiver physical interface is not

used in the system design, the CAN bus driver pins CANH and

CANL should be shorted together.

4.16.3. CANH

CANH is an output driver stage that sources current on the

CANH output. It’s output follows CANL, but in the opposite

polarity. The output is short circuit protected. In the event that

battery or ground is lost to the module, the CANH transmitter’s

output stage is disabled.

4.16.4. CANL

CANL is an output driver stage that sinks current on the

CANL output. The sink type output is short circuit protected.

In the event that battery or ground is lost to the module, the

CANL transmitter’s output stage is disabled.

4.16.5. CANTXD

CANTXD input comes from the microcontroller and drives

that state of the CAN bus pins, CANH and CANL. A logic ‘0’

input drives the outputs to a differential (dominant) voltage,

where the CANH output is +3.5 V and the CANL output is +1.5

V. A logic ‘1’ input drives the outputs to their idle (recessive)

state, where the CANH and CANL outputs are +2.5 V. An

internal pull–up to VDDH shall guarantee a logic ”1” input level

if this input is left open. On power–up, or in the event of a

thermal shutdown, this input must be toggled high and then

low to clear the thermal fault latch. The faulted CAN bus

output(s) will remain disabled until the thermal fault latch is

cleared. The CAN bus data rate is determined by the data rate

of CANTXD.

4.16.6. CANRXD

This is a CMOS compatible output used to send data from

the CAN bus pins, CANH and CANL, to the microprocessor.

When the voltage differential between CANH and CANL is

under the differential input voltage threshold (recessive state),

CANRXD is logic ‘1’. When the voltage differential between

CANH and CANL is over the voltage threshold (dominant

state), CANRXD is logic ‘0’. In standby mode, input voltage

threshold remains the same. There is a minimum of 0.1 V of

hysteresis between the high and low (and vice versa)

transition points.

Figure 10. CAN Transceiver Block Diagram

–

25 k

5 k

2.5 V

µA

0.8 – 2.0 V

0.5 – 1.0 V

CANRXD

AWAKE

CAN_EN

VDDH

OverTemp

Sense &

Hysteresis

VDDH

CAN_EN

CANL

CANH

CANTXD

CANRXD

Complimentary

High/Low Side

Drivers w/

Current Limit

4.16.7. CAN Over Temperature Latch Off Feature

If the CANH or CANL output is shorted to ground or battery

for any duration of time, an over temperature shut down circuit

disables the output stage. The output stage remains latched

off until the CANTXD input is toggled from a logic ’1’ to a logic

’0’ to clear the over temperature shutdown latch. Thermal

shutdown does not impact the remaining functionality of the

IC.

4.16.8. CAN Loss of Assembly Ground

The definition of a loss of ground condition at the device

level is that all pins of the IC (excluding transmitter outputs) will

see very low impedance to VBAT. The loss of ground is shown

on the module level in Figure 11. The nomenclature is suited

to a test environment. In the application, a loss of ground

condition results in all I/O pins floating to battery voltage. In

this condition, the CAN bus must not source enough current

to corrupt the bus.

4.16.9. CAN Loss of Assembly Battery

The loss of battery condition at the IC level is that the power

input pins of the IC see infinite impedance to the battery supply

voltage (depending upon the application) but there is some

undefined impedance looking from these pins to ground. In

this condition, the CAN bus must not sink enough current to

corrupt the bus. Refer to Figure 12.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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