33812 Datasheet, PDF (14/25 Pages) Freescale Semiconductor, Inc – SMALL ENGINE CONTROL IC

FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
The 33812 has two states of operation, Normal state and
Reset state.
RESET STATE
Applying V_PWR to the device will generate a Power On
RESET (POR) placing the device in the RESET state. The
Power On RESET circuit incorporates a timer to prevent high
frequency transients from causing an erroneous POR.
An under-voltage condition on VCC will also place the
device in the RESET state causing a RESET pulse to be
generated on the RESET line.
All RESETs will pre-load the watchdog timer with the
maximum time value, WD_MAX. The Watchdog will begin
counting on the rising edge of the pulse.
NORMAL STATE
The NORMAL State is entered after the RESET line goes
high.
Control register settings from RESET are as follows:
• All Outputs Off.
• Watchdog timer loaded with the WD_MAX time value.
Power Supply
The 33812 is designed to operate from 4.5 V to 36 V on
the VPWR pin. The VPWR pin supplies power to all internal
regulators, analog and logic circuit blocks. The VCCREF
output pin controls an external PNP bipolar transistor, such
that the collector is driven to +5.0 V +/- 2%. The VCCSENS
input pin, connected to the collector of the PNP, is used to
monitor the output voltage and provides the feedback to
regulate the PNP collector to +5.0 V.
INJECTOR DRIVER OPERATION
The open drain Low Side Driver (LSD) INJOUT is
designed to control a fuel injector. The Injector Driver is
controlled through the logic level parallel input pin, INJIN.
When INJIN is high, the INJOUT pin is pulled to ground,
turning on the fuel injector. When INJIN is low, the injector
pulls the INJOUT output to VBAT and the injector is turned
off.
The INJOUT driver includes off state open load detection
and it’s output device is protected against over-current, short
to battery, over-temperature, inductive flyback over-voltage
and VPWR over-voltage.
INJOUT Output Protection Features
Over-current (I_OUT-LIM)
The Injector Driver protection scheme uses three separate
protection schemes to prevent damage to the output device.
The first protection scheme is deployed when an over-
current event occurs. In this case the current limiting circuitry
will attempt to limit the maximum current flow to the specified
I_LIM-INJ value.
Short to Battery
The second protection scheme is invoked when the over-
current fault is due to a hard short to battery. In this case, the
protection circuitry will, after the short detection filter time,
turn off the output driver. The output will not try to turn on
again until the INJIN input goes low and then high again.
A short to battery is reported as a high logic level on the
INJFLT line.
Temperature Limit (T_LIM)
The third protection scheme deals with the junction
temperature of the output device. Any time the maximum
temperature limit on the output device is exceeded (T_LIM), the
device will shutdown until the junction temperature falls below
this maximum temperature minus the hysteresis temperature
value. The T_LIM hysteresis value is T_LIM(HYST).
The maximum temperature (T_LIM) protection scheme
controls the output device regardless of the state of the INJIN
input. The device is unable to be activated until the junction
temperature falls below this maximum temperature minus the
hysteresis temperature value.
An over-temperature fault is also reported as a high logic
level on the INJFLT line.
Over-voltage (V_CLAMP-INJ and V_PWR(OV))
The injector driver is also protected against two types of
over-voltage conditions:
When the V_PWR supply exceeds the V_PWR(OV) threshold,
the INJOUT output turns off and stays off until the over-
voltage condition abates and the INJIN input pin toggles low
and then high again.
The output device controls inductive flyback voltages by
an active clamping network that limits the voltage across the
output device to V_CLAMP-INJ volts.
33812
14
Analog Integrated Circuit Device Data
Freescale Semiconductor