33894 Datasheet, PDF (18/28 Pages) Freescale Semiconductor, Inc – Quad High-Side Switch

FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
Loss of V_DD
If the external 5.0 V supply is not within specification, or
even disconnected, all register content is reset. The outputs
can still be driven by the direct inputs IN0 : IN3. The 33894
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 V_DD supplied. In this state,
the watchdog, overvoltage, overtemperature, and
overcurrent circuitry are fully operational with default values.
FAULT MODE
This 33894 indicates the faults below 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 faults.
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 16, page 23).
Overtemperature Fault (Non-Latching)
The 33894 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 T_SD(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.
Overvoltage Fault (Non-Latching)
The 33894 shuts down the output during an overvoltage
fault (OVF) condition on the V_PWR 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 the bit
D1 and cleared after either a valid SPI read or a power reset
of the device.
The overvoltage protection can be disabled through SPI
(bit OV_DIS). When disabled, the returned SO bit OD13 still
reflects any overvoltage condition (overvoltage warning).
Undervoltage Shutdown (Latching or Non-Latching)
The output latches OFF at some battery voltage between
4.75 V and 5.75 V. As long as the V_DD level stays within the
normal specified range, the internal logic states within the
device will be sustained. This ensures that when the battery
level then returns above 5.75 V, the 33894 can be returned
to the state that it was in prior to the low V_PWR excursion.
Once the output latches OFF, the outputs must be turned
OFF and ON again to re-enable them. In the case
IN1 : IN0 = 0, this fault is non-latched.
The undervoltage protection can be disabled through SPI
(bit UV_DIS). When disabled, the returned SO bit OD14 still
reflects any undervoltage condition (undervoltage warning).
Open Load Fault (Non-Latching)
The 33894 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 will be cleared after reading the register.
The open load protection can be disabled trough SPI (bit
OL_DIS).
Overcurrent Fault (Latching)
The 33894 has eight programmable overcurrent low
detection levels (I_OCL) and two programmable overcurrent
high detection levels (I_OCH) for maximum device protection.
The two selectable, simultaneously active overcurrent
detection levels, defined by I_OCH and I_OCL, are illustrated in
Figure 6, page 14. The eight different overcurrent low detect
levels (I_OCL0 : I_OCL7) are illustrated in Figure 6.
If the load current level ever reaches the selected
overcurrent low detection level and the overcurrent condition
exceeds the programmed overcurrent time period (t_OCx), the
device will latch the output OFF.
If at any time the current reaches the selected I_OCH level,
then the device will immediately latch the fault and turn OFF
the output, regardless of the selected t_OCLx 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 gate is
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.
GROUND DISCONNECT PROTECTION
In the event the 33894 ground is disconnected from load
ground, the device protects itself and safely turns OFF the
output regardless of the state of the output at the time of
disconnection.
33894
18
Analog Integrated Circuit Device Data
Freescale Semiconductor