33812 datasheet(14/25 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33812

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 VPWR 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, WDMAX. 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 WDMAX 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 (IOUT-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

ILIM-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 (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 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 (VCLAMP-INJ and VPWR(OV))

The injector driver is also protected against two types of

over-voltage conditions:

When the VPWR supply exceeds the VPWR(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 VCLAMP-INJ volts.

33812 Datasheet(PDF) 14 Page - Freescale Semiconductor, Inc

33812 Datasheet(HTML) 14 Page - Freescale Semiconductor, Inc

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