33812 Datasheet, PDF (17/25 Pages) Freescale Semiconductor, Inc – SMALL ENGINE CONTROL IC

FUNCTIONAL DEVICE OPERATION
LAMP DRIVER OPERATION
LAMP DRIVER OPERATION
The Lamp Driver is a low side driver that is controlled by
the logic level LAMPIN input pin. When LAMPIN is high, the
LAMP pin is pulled to ground, turning on an external bulb or
LED. When LAMPIN is low, the bulb or LED pulls the LAMP
output to V_BAT, and the lamp is turned off.
LAMPOUT Protection Features
Over-current (I_OUT-LIM-LAMP)
The LAMPOUT 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-LAMP} 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.
There will be an internal retry timer to try to turn on again
if the fault clears.
There is no annunciation of any LAMPOUT faults.
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
LAMPIN input. The device is unable to be activated until the
junction temperature falls below this maximum temperature
minus the hysteresis temperature value.
LAMPOUT FAULT DETECTION FEATURES
Off State, Open Load Detection
Since there is no way to annunciate an open load fault for the
lamp output driver, no open load fault detection is performed
by the 33812.
On State, Shorted Load Detection
performed by the 33812 as part of the protection for the
output FET.
The LAMPOUT driver also has an over-current blanking
time of t_OC(BLANK) to allow for incandescent lamp inrush
current
Even though there is no way to annunciate a shorted load
fault for the lamp output driver, shorted fault detection is
OVER/UNDER-VOLTAGE SHUTDOWN STRATEGY
How the outputs behave after an over-voltage or under-
voltage event on VPWR is listed in Table 3 below:
Table 3. Over-voltage/Under-voltage Truth Table
State
Output
Before OV
or UV
State When
Returning From
Over-voltage
State When
Returning From
Under-voltage
INJOUT
X
OFF
OFF
IGNOUT
X
OFF
OFF
ROUT
OFF ^OFF
OFF
ROUT
ON ^ON
OFF
LAMPOUT OFF ^OFF
OFF
LAMPOUT ON ^ON
OFF
Analog Integrated Circuit Device Data
Freescale Semiconductor
33812
17