33888 Datasheet, PDF (21/40 Pages) Freescale Semiconductor, Inc – Quad High-Side and Octal Low-Side Switch for Automotive

FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
The FS pin is driven to a logic [0] when a fault exists on any
of the outputs. FS provides real time monitoring of the
overvoltage fault. For the high-side outputs, FS provides real
time monitoring of the open load and overtemperature. For
the low-side outputs, the FS is latched to a logic [0] for open
load, overtemperature, and overcurrent faults. The latch is
cleared by toggling the state of the faulted output or by
bringing RST low.
OVERTEMPERATURE FAULT
The 33888 incorporates overtemperature detection and
shutdown circuitry into each individual output structure.
Overtemperature detection occurs when an output is in the
ON state. When an output is shut down due to an
overtemperature condition, no other output is affected. The
output experiencing the fault is shut down to protect itself
from damage. A fault bit is loaded into the status register if the
overtemperature condition is removed, and the fault bit is
cleared upon the rising edge of CS.
For the low-side outputs, the faulted output is latched OFF
during an overtemperature condition. If the temperature falls
below the recovery level, T_LIM(HYS), then the output can be
turned back ON only after the output has first been
commanded OFF either through the SPI or the ILS,
depending on the logic configuration.
For the high-side output(s), an overtemperature condition
will result in the output(s) turning OFF until the temperature
falls below the T_LIM(HYS). This cycle will continue indefinitely
until action is taken by the MCU to shut the output(s) OFF.
LOW = Logic 0
+
–
33888
OVERVOLTAGE FAULT
The 33888 shuts down all outputs during an overvoltage
condition on the V_PWR pin. The outputs remain in the OFF
state until the overvoltage condition is removed. Fault status
for all outputs is latched into the status register. Following an
overvoltage condition, the next write cycle sent by the SO pin
of the 33888 is logic [1] on OD11: OD0, indicating all outputs
have shut down. If the overvoltage condition is removed, the
status register can be cleared by a rising edge on CS.
OPEN LOAD FAULT
The 33888 incorporates open load detection circuitry on
every output. A high-side or low-side output open load fault is
detected and reported as a fault condition when the
corresponding output is disabled (OFF) if it was configured
for open load detection by setting the appropriate bit to
logic [0] (HS3 : HS0) or logic [1] (LS11: LS4) in the OLFCR
register (see Figure 7).
The high-side 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. If the open load fault is removed
or if the faulted output is commanded ON, the status register
can be cleared by a rising edge on CS. Note that the device
default state will enable the high-side open load detection
and disable the low-side open load detection circuits,
respectively.
It is recommended to disable the open load detection
circuitry (OL bit sets to logic [1]) in case of a permanent open
load fault condition.
MOSFET
50 mA
V_PWR
R_L
OUT
V_THRES ^VOFD(THRES)LS
2.0 V–4.0 V
Figure 7. Low-Side Output OFF Open Load Detection
OVERCURRENT FAULT REQUIREMENTS: LOW-
SIDE OUTPUT
An overcurrent condition is defined as any current value
greater than I_LIM (500 mA minimum value for LS5, LS7, LS9,
LS11, and 800 mA minimum value for LS4, LS6, LS8, LS10).
The status of the corresponding bit in the CLOCCR register
determines whether a specific output shuts down or
continues to operate in an analog current limited mode until
either the overcurrent condition is removed or the thermal
shutdown limit is reached (Figure 10, page 27). If the
overcurrent shutdown mode is disabled, the fault reporting is
disabled as well.
For the low-side output of interest, if a D11: D4 bit was set
to a logic [1] in the OLCR register, the overcurrent protection
shutdown circuitry will be enabled for that output. When a
low-side output is commanded ON either from the SPI or the
ILS pin, the drain of the low-side driver will be monitored for
a voltage greater than the fault detection threshold (3.0 V
typical). If the drain voltage exceeds this threshold, a timer
will start and the output will be turned off and a fault latched
in the status register after the timeout expires. The faulted
output can be retried only by commanding the output OFF
and back ON either through the SPI or the ILS pin, depending
on the logic configuration. If the fault is gone, the retried
output will return to normal operation and the status register
can be cleared on a rising edge of CS. If the fault remains, the
Analog Integrated Circuit Device Data
Freescale Semiconductor
33888
21