33810 datasheet(28/37 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33810

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

protection circuit uses the junction temperature of the output

driver to determine the fault. Both methods may be used

together or individually.

TIMER PROTECTION

The first protection scheme uses a low ON to OFF duty

cycle to protect the output driver. The low duty cycle allows

the device to cool so that the maximum junction temperatures

are not exceeded. During a short condition, the device enters

current limit. The driver will shutdown for short conditions

lasting longer than the current limit timer (~60

μs)

TEMPERATURE LIMIT (TLIM)

The second scheme senses the temperature of the

individual output driver. During a short event the device

enters current limit and will remain in current limit until the

output driver temperature limit is exceeded (TLIM). At this

point, the device will shutdown until the junction temperature

falls below the hysteresis temperature value. The TLIM

hysteresis value is listed in the previous specification tables.

The third method combines both protection schemes into

one. During a short event the device will enter current limit.

The output driver will shutdown for short conditions lasting

longer than the current limit timer. In the event that the output

driver temperature is higher than maximum specified

temperature the output will shutdown.

The Shutdown/Retry bit allows the user to determine how

the drivers will respond to each short circuit strategy.

Table 18 provides fault operation for all three strategies.

Outputs may be used in parallel to drive higher current

loads provided the turn-off energy of the load does not

exceed the energy rating of a single output driver (100mJ

maximum).

Table 18.

Shutdn

Retry

Bit 11

TLIM

Bit 10

Fault

Timer

Bit 9

Operation During Short Fault

Timer only, Outputs will retry on period

OUT0-OUT3 = 60

μs ON, ~10ms OFF

TLIM only, Outputs will retry on TLIM

hysteresis.

Timer and TLIM, Outputs will retry on

period and driver temperature below

threshold.

OUT0-OUT3= 60

μs ON, ~10ms OFF

Timer only, Outputs will not retry on

period

OUT0-OUT3 = 60

μs ON, OFF

TLIM only, Outputs will not retry on TLim

hysteresis.

Timer and TLIM, Outputs will not retry on

period or TLIM.

OUT0-OUT3 = 60

μs ON, OFF

Injector Driver (OUTx) Fault Operation

OUTPUT DRIVER DIAGNOSTICS.

Short to battery, Temperature Limit (TLIM) and open load

faults are reported through the All Status Response message

Table 21.

OFF OPEN LOAD PULL-DOWN CURRENT ENABLE

BITS

An open load on the output driver is detected by the

voltage level on the drain of the MOSFET in the off state.

Internal to the device is a 75

μA pull-down current sink. In the

event of an open load the drain voltage is pulled low. When

the voltage crosses the threshold, and open load is detected.

The pull-down current source may be disabled by bit 0

through bit 3 in the LSD Fault Command. With the driver off

and the Off Open Load bit disabled, the Off Open Load fault

status bit will be logic 0.

ON OPEN LOAD ENABLE BITS

The On State Open Load enable bit allows the user to

determine an On State Open Load. When the On State Open

Load bit disabled, the On State Fault bit is always logic 0. On

Open Load is determined by monitoring the current through

the OUTx MOSFET. In the ON state, currents less than 20 to

200mA are considered open.

33810 Datasheet(PDF) 28 Page - Freescale Semiconductor, Inc

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