33812 Datasheet, PDF (15/25 Pages) Freescale Semiconductor, Inc – SMALL ENGINE CONTROL IC

FUNCTIONAL DEVICE OPERATION
IGNITION PRE-DRIVER OPERATION
INJOUT Fault Detection Features
Off State, Open Load Detection
An open load on the injector driver is detected by the
voltage level on the drain of the output device in the off state.
Internal to the device is a pull-down current source. In the
event of an open injector the drain voltage is pulled low.
When the voltage crosses the open load detection threshold,
an open load is detected. The open load fault detect
threshold is set internally and is not programmable. The open
load fault is reported as a high logic level on the INJFLT line.
On State, Shorted Load Detection
The INJOUT driver is capable of detecting a shorted
injector load (short to battery) in the on state. A shorted load
fault is reported when the drain pin voltage is greater than the
preset short threshold voltage. The shorted load fault detect
threshold is set internally and is not programmable. The
shorted load fault is reported as a high logic level on the
INJFLT line.
Clearing the INJFLT line
When the INJFLT line goes high for any of the following
reasons, while the INJIN line is high (on state):
• Short to battery
• Over-temperature
• Over-voltage
• Open load
The INJFLT line will remain high until the INJIN line goes
to a low logic level and the returns high (rising edge).
IGNITION PRE-DRIVER OPERATION
The Ignition pre-driver output is controlled by the logic
level input IGNIN. When IGNIN is high the IGNOUTH pin is
pulled high to IGNSUP. When the IGNIN pin is low, the
IGNOUTL line is pulled to ground turning off the driver
Darlington or IGBT.The IGNOUT pre-driver protects the
output device against over-current, short to battery, and
VPWR over-voltage.
output device in the off state (through a 10:1 voltage divider).
In the event of an open ignition coil the drain/collector voltage
is pulled low. When the voltage crosses the open load
detection threshold, an open load is detected. The open load
fault detect threshold is set internally and is not
programmable. An open load fault is reported as a high logic
level on the IGNFLT line.
IGNOUT OUTPUT PROTECTION FEATURES
Over-current and Short to battery (I_LIM)
The Ignition Pre-driver protection scheme senses over-
current in the driver device by monitoring the voltage at the
IGNFB pin. Since this pin is protected by a 10:1 voltage
divider, the over-current threshold voltage is set internally to
1/10 of the voltage expected on the drain or collector of the
output device in an over-current situation. Since the Ignition
output device is external to the 33812, a short to battery is the
same as an over-current fault.
An over-current fault or short to battery is reported as a
high logic level on the IGNFLT line.
Temperature Limit (T_LIM)
Since the Ignition output device is external to the 33812,
there is no over-temperature protection provided.
IGNOUT FAULT DETECTION FEATURES
Over-voltage (V_PWR(OV))
The Ignition pre-driver is also protected against an over-
voltage condition:
When the VPWR supply exceeds the V_PWR(OV) threshold,
the IGNOUTL and IGNOUTH outputs turn off and stays off
until the over-voltage condition clears and the next rising
edge of the IGNIN input pin.
Clearing the IGNFLT line
When the IGNFLT line goes high for any of the following
reasons, while the IGNIN line is high (on state):
• Short to battery
• Over-voltage
• Over-temperature of the IGNOUTL and IGNOUTH
transistors
• Open load
The IGNFLT line will remain high until the IGNIN line goes
to the low logic level and then returns high.
Off State, Open Load Detection
An open load on the ignition driver external device is
detected by the voltage level on the drain or collector of the
Analog Integrated Circuit Device Data
Freescale Semiconductor
33812
15