33812 Datasheet, PDF (16/25 Pages) Freescale Semiconductor, Inc – SMALL ENGINE CONTROL IC

FUNCTIONAL DEVICE OPERATION
RELAY DRIVER OPERATION
RELAY DRIVER OPERATION
The Relay Driver (ROUT) is a low side driver that is
controlled by the logic level RIN input pin. When RIN is high,
the ROUT pin is pulled to ground, turning on an external relay
or other device. When RIN is low, the relay coil pulls the
ROUT output to V_BAT, and the relay is turned off.
The ROUT 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.
The Relay Driver is functionally and electrically identical to
the Injector driver and can be used as a second Injector
driver, for two cylinder applications, as long as maximum
power dissipation considerations are observed.
ROUT PROTECTION FEATURES
Over-current (I_{OUT-LIM ROUT})
The ROUT 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_{OUT LIM-REL}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 RIN input goes low and then high again.
A short to battery is reported as a high logic level on the
RELFLT 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 RIN
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 RELFLT line.
Over-voltage (V_CLAMP-RELand V_PWR(OV))
The relay driver is also protected against two types of
over-voltage conditions:
When the VPWR supply exceeds the V_PWR(OV) threshold,
the ROUT output turns off and stays off until the over-voltage
condition abates and the RN input pin toggles low and then
high again.
The output device is protected against inductive flyback
voltages greater than V_CLAMP-REL by an active clamping
network that limits the voltage across the output device to
V_CLAMP-REL volts.
ROUT FAULT DETECTION FEATURES
Off State, Open Load Detection
An open load on the relay 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 RELFLT line.
On State, Shorted Load Detection
The ROUT driver is capable of detecting a shorted 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
RELFLT line.
Clearing the RELFLT line
When the RELFLT line goes high for any of the following
reasons, while the RIN line is high (on state):
• Short to battery
• Over-temperature
• Over-voltage
• Open load
The RELFLT line will remain high until the RIN line goes to
a low logic level and the returns high (rising edge).
33812
16
Analog Integrated Circuit Device Data
Freescale Semiconductor