33989 datasheet(52/66 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33989

TYPICAL APPLICATIONS

SUPPLEMENTAL APPLICATION NOTES

CAN Driver Overtemperature:

In case of an overtemperature condition at the CANH or

CANL driver, the driver will be automatically disabled and the

THERM bit set in the CAN register. If enabled, an interrupt

will be signalled. The GFAIL flag is set in the MCR register.

When the CAN is in an overtemperature situation, the

device is no longer able to transmit. As soon as the

temperature is below the overtemperature level minus

hysteresis, the CAN driver is automatically re-enabled.

The THERM bit is latched and two conditions are

necessary to clear it:

• No longer “CAN overtemperature situation” AND

• Read operation of the CAN register.

Overcurrent Detection:

The CAN interface can detect and signal over current

condition, occurring for instance in case of CANL shorted to

VBAT. This is signalled by the bit CUR in the CAN register.

An INT can be enabled, and GFAIL bit is set. The CUR bit is

latched and two conditions are necessary to clear it:

• No longer “CAN over current situation” AND

• Read operation of the CAN register.

Protection

The MC33989 CAN output is protected for automotive

environments.

The CAN driver is protected against overtemperature and

overcurrent.

ISO7637 Transient

The CANH and CANL are rated from +40 Vdc to -27 Vdc.

This means that the MC33989 CAN output can handle failure

situations like the bus directly shorted to the battery line in a

load dump situation (+40 V).

Ground disconnection of the module will lead to the CANH

and CANL line floating high to the VBAT supply. The rest of

the network will not be affected. However the CANH and

CANL lines of the ungrounded module will see a negative

voltage of the VBAT value, with respect to their gnd level.

Such situations can be handled by the CAN interface of the

MC33989, but also in cases of a jump start (battery at 27 V)

and gnd disconnection.

Fast transient pulses, ISO7637-3. During these pulses, the

maximum rating of the CANH and CANL lines of +40 Vdc and

-27 Vdc must be respected.

ESD

The CANH and CANL line of the MC33989 are rated at

±4 kV. An external capacitor between CANH and CANL to

gnd or a zener diode suppressor can be added to ensure a

higher module resistance to ESD.

Current in Case of Bus Short Conditions

In case of short circuit condition on the CAN bus the

current in the CAN supply, the CAN line can be different from

the nominal case. The Figure 44 and Table 35 describe the

various cases.

Figure 44. Current in Case of Bus Short Conditions

V2 Terminal

60 ohms

CANH line

CAN L line

I_H

I_L

I_TERM

CANH

CANL

VBAT

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