33984B datasheet(21/38 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33984

FUNCTIONAL DEVICE OPERATION

PROTECTION AND DIAGNOSIS FEATURES

FAULT MODE

The 33984 indicates the following faults as they occur by

driving the FS pin to Logic [0]:

• Over-temperature fault

• Open load fault

• Over-current fault (high and low)

• Over-voltage and under-voltage fault

The FS pin will automatically return to Logic [1] when the

fault condition is removed, except for over-current and in

some cases under-voltage.

Fault information is retained in the fault register and is

available (and reset) via the SO pin during the first valid SPI

communication (refer to Table 17).

PROTECTION AND DIAGNOSIS FEATURES

OVER-TEMPERATURE FAULT (NON-LATCHING)

The 33984 incorporates over-temperature detection and

shutdown circuitry in each output structure. Over-

temperature detection is enabled when an output is in the ON

state.

For the output, an over-temperature fault (OTF) condition

results in the faulted output turning OFF until the temperature

falls below the TSD(HYS). This cycle will continue indefinitely

until action is taken by the MCU to shut OFF the output, or

until the offending load is removed.

When experiencing this fault, the OTF fault bit will be set

in the status register and cleared after either a valid SPI read

or a power reset of the device.

OVER-VOLTAGE FAULT (NON-LATCHING)

The 33984 shuts down the output during an over-voltage

fault (OVF) condition on the VPWR pin. The output remains

in the OFF state until the over-voltage condition is removed.

When experiencing this fault, the OVF fault bit is set in the bit

OD1 and cleared after either a valid SPI read or a power reset

of the device.

The over-voltage protection and diagnostic can be

disabled trough the SPI (bit OV_dis).

UNDER-VOLTAGE SHUTDOWN (LATCHING OR

NON-LATCHING)

The output(s) will latch off at some battery voltage below

6.0 V. As long as the VDD level stays within the normal

specified range, the internal logic states within the device will

be sustained.

In the case where battery voltage drops below the under-

voltage threshold (VPWRUV) output will turn off, FS will go to

Logic [0], and the fault register UVF bit will be set to 1.

Two cases need to be considered when the battery level

recovers :

• If output(s) command is (are) low, FS will go to Logic [1]

but the UVF bit will remain set to 1 until the next read

operation.

• If the output command is ON, then FS will remain at

Logic [0]. The output must be turned OFF and ON again

to re-enable the state of output and release FS . The

UVF bit will remain set to 1 until the next read operation.

The under-voltage protection can be disabled through the

SPI (bit UV_dis = 1). In this case, the FS and UVF bits do not

report any under-voltage fault condition and the output state

will not be changed as long as battery voltage does not drop

any lower than 2.5 V.

OPEN LOAD FAULT (NON-LATCHING)

The 33984 incorporates open load detection circuitry on

each output. Output open load fault (OLF) is detected and

reported as a fault condition when that output is disabled

(OFF). The open load fault is detected and latched into the

status register after the internal gate voltage is pulled low

enough to turn OFF the output. The OLF fault bit is set in the

status register. If the open load fault is removed, the status

The open load protection can be disabled trough SPI (bit

OL_dis).

It is recommended to disable the open load

detection circuitry (OL_dis bit sets to logic [1]) in case

of permanent open load fault condition.

OVER-CURRENT FAULT (LATCHING)

The device has eight programmable over-current low

detection levels (IOCL) and two programmable over-current

high detection levels (IOCH) for maximum device protection.

The two selectable, simultaneously active over-current

detection levels, defined by IOCH and IOCL, are illustrated in

Figure 6. The eight different over-current low detect levels

(IOCL0:IOCL7) are likewise illustrated in Figure 6.

If the load current level ever reaches the selected over-

current low detect level and the over-current condition

exceeds the programmed over-current time period (tOCx), the

device will latch the effected output OFF.

If at any time the current reaches the selected IOCH level,

then the device will immediately latch the fault and turn OFF

the output, regardless of the selected tOCL driver.

For both cases, the device output will stay off indefinitely

until the device is commanded OFF and then ON again.

REVERSE BATTERY

The output survives the application of reverse voltage as

low as -16 V. Under these conditions, the output’s gates are

enhanced to keep the junction temperature less than 150°C.

The ON resistance of the output is fairly similar to that in the

Normal mode. No additional passive components are

required.

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