33812 datasheet(16/25 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33812

FUNCTIONAL DEVICE 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 VBAT, 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 (IOUT-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

IOUT LIM-RELvalue.

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 (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 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 (VCLAMP-RELand VPWR(OV))

The relay driver is also protected against two types of

over-voltage conditions:

When the VPWR supply exceeds the VPWR(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 VCLAMP-REL by an active clamping

network that limits the voltage across the output device to

VCLAMP-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 Datasheet(PDF) 16 Page - Freescale Semiconductor, Inc

33812 Datasheet(HTML) 16 Page - Freescale Semiconductor, Inc

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