33812 datasheet(17/25 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33812

FUNCTIONAL DEVICE 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 VBAT, and the lamp is turned off.

LAMPOUT Protection Features

Over-current (IOUT-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

IOUT 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 (TLIM)

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 (TLIM), the

device will shutdown until the junction temperature falls below

this maximum temperature minus the hysteresis temperature

value. The TLIM hysteresis value is TLIM(HYST).

The maximum temperature (TLIM) 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

Even though there is no way to annunciate a shorted load

fault for the lamp output driver, shorted fault detection is

performed by the 33812 as part of the protection for the

output FET.

The LAMPOUT driver also has an over-current blanking

time of tOC(BLANK) to allow for incandescent lamp inrush

current

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

Output

State

Before OV

or UV

State When

Returning From

Over-voltage

State When

Returning From

Under-voltage

INJOUT

OFF

IGNOUT

OFF

ROUT

OFF

ROUT

OFF

LAMPOUT

OFF

LAMPOUT

OFF

33812 Datasheet(PDF) 17 Page - Freescale Semiconductor, Inc

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