PC33882R2 datasheet(18/31 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33882

FUNCTIONAL DESCRIPTION

FUNCTIONAL PIN DESCRIPTION

The low duty cycle operation for a short-circuit condition is

required to protect the output. It is possible to override this

duty cycle if the input signal (parallel or SPI) turns the channel

ON and OFF faster than 10 kHz. For this reason control

signals should not exceed this frequency.

OPEN LOAD/SHORT-TO-GROUND WHILE OFF

SENSING

If the drain voltage falls below the Open Load OFF

Detection Voltage at turn OFF for a period of time exceeding

the Open Load Sense Time, the fault status bit for this output

switches to a logic [1].

If a drain voltage falls below the Open Load OFF Detection

Voltage threshold when the output has been OFF, a fault is

indicated with a delay much less than the Open Load Sense

Time. When the fault is removed, normal operation resumes

and the fault status bit will return to a normal logic [0] state.

When the CS pin of this device is pulled low, the fault status

bits are latched, after which any new fault information is not

part of this serial communication event.

OVER-VOLTAGE SENSING AND PROTECTION

When VPWR exceeds the Over-voltage Shutdown

Threshold, all channels are shut down. Serial input data and

parallel inputs are ignored. The device resumes normal

operation when the VPWR voltage drops below the Over-

voltage Shutdown Hysteresis voltage. During over-voltage

shutdown, some faults may appear to report accurately;

however, fault sensing operation is only guaranteed for

battery voltage levels from 9.0 V to 17 V.

FAULT STATUS MONITORING REQUIREMENTS

FOR SERIALLY CONTROLLED OUTPUTS, SO PIN

Fault monitoring over the serial channel by the IC requires

a minimal amount of overhead for normal operation. Each

status byte received consists of all logic [0]s when faults are

not present. If any logic [1]s are returned, a communication

error occurred, an output fault occurred, or the MODE pin has

been set low. Upon receiving any logic [1] bits, the IC must

resend the last command, verifying the returned logic [1]s, or

correct any communication error.

A 16-bit SPI transmission with a double command byte to

this 8-bit device allows verification of the command (second

byte returned) in addition to the fault byte (first byte returned).

The command (second) byte returned should mirror the bits

sent unless a communication error occurred, in which case

the command resent should accomplish the correction.

If the returned logic [1] validates, it may indicate a MODE

pin high or a confirmed output fault. If it was a confirmed

output fault, extensive diagnostics could be performed,

determining the fault type, especially if vehicle service is

being performed. If all bits return high and verify such, the IC

must verify sending a logic low to the MODE pin. It should

then resend the command, verifying the MODE pin is at a

logic low level, allowing resumption of a normal operation. If

all logic [1]s are again returned, there is an open SO line, an

open MODE line, or the SPI is not functioning.

If the fault does not verify on the command resend, normal

operation is resumed. The error could be a communication

mistake, a momentary output fault, or a fault condition no

longer sensed due to switching the state of the output. For the

first two cases, normal operation is resumed and the software

continues its normal functions. However in the third case,

additional commands are required for extensive diagnosis of

the fault type, if this information is mandatory.

EXTENSIVE FAULT DIAGNOSTICS

More extensive diagnosis may be required under the

following conditions:

• When the fault type of a confirmed fault is desired, the

following scenarios are possible:

–

If MSB-2 to MSB-7 indicates a fault, it is an open

load/short-to-ground fault if the output is OFF when

the fault is reported because only open load/short-

to-ground sensing remains operable while an output

is OFF.

–

If the output is ON when the fault is reported, the

fault is a short-circuit/short-to-battery if ON open

load detection is not enabled via SPI. If ON open

load detection is enabled, it must be disabled and

the fault status reread. If the fault remains, it is a

short-circuit/short-to-battery or it is an open load/

short-to-ground.

–

If MSB-0 to MSB-2 indicates a fault, it is an open

load/short-to-ground fault if the output is OFF when

the fault is reported because only open load/short-

to-ground sensing remains operable while an output

is OFF.

–

If the output is ON when the fault is reported, the

fault is a short-circuit/short-to-battery.

• When a fault did not confirm on resend, the fault could

either be an short-circuit/short-to-battery fault, not sensed

when turned OFF; an open load/short-to-ground fault, not

sensed when turned ON; or a corrected communication

error.

To determine if it is an output fault condition, the faulted

output must be turned back to its previous state with a new

command. This command should be sent twice to read the

status after the output is latched in this state, thus

confirming the fault and reporting it again.

Parallel control of outputs is a mode of control, potentially

requiring extensive diagnostics if a fault is reported. This is

because parallel control signals are completely

asynchronous to the serial commands. Status reports for

parallel controlled outputs could require additional

information exchange in software to:

• Avoid status reads when outputs are transitioned, thereby

avoiding fault masking times.

• Obtain the state of a faulted output for determining fault

type (if required).

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