NXP Semiconductors

21

33982

FUNCTIONAL DEVICE OPERATION

If the FSI pin is tied to GND, the Watchdog Fail-safe operation is disabled.

LOSS OF VDD

If the external 5.0 V supply is not within specification, or even disconnected, all register content is reset. The output can still be driven by

the direct input IN. The 33982 uses the battery input to power the output MOSFET related current sense circuitry, and any other internal

logic, providing fail-safe device operation with no VDD supplied. In this state, the watchdog, overvoltage, overtemperature, and overcurrent

circuitry are fully operational with default values. Current recopy is active with the default current recopy value.

FAULT MODE

The 33982 indicates the following faults as they occur by driving the FS pin to logic [0]:

• Overtemperature fault

• Overvoltage and undervoltage fault

• Open load fault

• Overcurrent fault (high and low)

The FS pin automatically returns to logic [1] when the fault condition is removed, except for overcurrent and in some cases undervoltage.

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 diagnostic features

OVERTEMPERATURE FAULT (NON-LATCHING)

The 33982 incorporates overtemperature detection and shutdown circuitry in the output structure. Overtemperature detection is enabled

when the output is in the ON state.

For the output, an overtemperature fault (OTF) condition results in the faulted output turning OFF until the temperature falls below the

TSD(HYS). This cycle continues 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 is set in the status register and cleared after either a valid SPI read or a power reset of the

device.

OVERVOLTAGE FAULT (NON-LATCHING)

The 33982 shuts down the output during an overvoltage fault (OVF) condition on the VPWR pin. The output remains in the OFF state until

the overvoltage condition is removed. When experiencing this fault, the OVF fault bit is set in bit OD1 and cleared after either a valid SPI

read or a power reset of the device. The overvoltage protection and diagnostic can be disabled through the SPI (bit OV_dis).

UNDERVOLTAGE SHUTDOWN (LATCHING OR NON-LATCHING)

The output(s) latches 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 is sustained.

In cases where the battery voltage drops below the undervoltage threshold, (VPWRUV) the output turns off, FS goes to logic [0], and the

fault register UVF bit is set to 1.

Two cases need to be considered when the battery level recovers:

• If the output(s) command is (are) low, FS goes to logic [1], but the UVF bit remains set to 1 until the next read operation.

• If the output command is ON, then FS remains 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 remains set to 1 until the next read operation.

The undervoltage protection can be disabled through the SPI (bit UV_dis = 1). In this case, the FS and UVF bits do not report any

undervoltage fault condition and the output state is not changed as long as the battery voltage does not drop any lower than 2.5V.

OPEN LOAD FAULT (NON-LATCHING)

The 33982 incorporates open load detection circuitry on the output. Output open load fault (OLF) is detected and reported as a fault

condition when the 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 register is cleared after reading the register.

The open load protection can be disabled through the SPI (bit OL_dis). It is recommended to disable the open load detection circuitry:

(OL_dis bit sets to logic [1]) in case of a permanent open load fault condition.

OVERCURRENT FAULT (LATCHING)

The 33982 has eight programmable overcurrent low detection levels (IOCL) and two programmable overcurrent high detection levels

(IOCH) for maximum device protection. The two selectable, simultaneously active overcurrent detection levels, defined by IOCH and IOCL,

are illustrated in Figure 6. The eight different overcurrent low detection levels (IOCL0:IOCL7) are likewise illustrated in Figure 6.