PIN FUNCTIONS (refer to fig. 2)

N

°

Name

Function

1

CURRENT SENSING

INPUT

Connection for Coil Current Limitation. The current is measured on the

given by :

=

R1

+ R2

2

PICKUP INPUT

Magnetic Pickup Signal Input. This pin sets the dwell time,

i.e. the max

negative pickup voltage value starting from which the device can drive the

current into the coil. The real dwell time will be a function of the dwell

control logic. Increasing the resistor R11 the maximum conduction time

increases. The max input current foreseen is 2mA.

3

PERMANENT

CONDUCT.

PROTECTION TIMER

A capacitor C1 connected between this pin and ground sets the delay of the

permanent conduction protection in the coil current. Using a 50nF capacitor

the typical desaturation time delay for the protection is 75ms.

4

PERMANENT CONDUCT.

PROTECTION INHIBIT

A low level on this input (max 0.7V) disables the protection, irrespective of

the state of pin 3. If the protection is used this pin must be left open.

5

RPM OUTPUT

Open collector output signal which is at a low level when the final darlington

is in ON status. The current is internally limited at 10mA.

6

DWELL TIME ADJUST

At high motor rotation speeds,

i.e. when the peak value of the magnetic

pick-up signal exceedes 6V using R12 = 100K

Ω, this pin may be used to

11 the desaturation time is reduced. It is therefore possible to use this pin to

adapt the L484 to various pickup types. The maximum value of the resistor

Ω.

7

DWELL CONTROL

TIMER

A capacitor C2 connected between this pin and ground sets the timing for

provide an hysteresis to confirm ON state and avoid spurious sparks.

8

ZERO CROSSING

INPUT

Zero cross detector input of the magnetic pickup signal for the ignition

actuation. At high motor rotation speeds, the external resistor R12 may be

used to vary the

desaturation time ratio,

to adapt the L484 to various

signal waveforms of time magnetic pick-up. Reducing the resistor value the

dwell time increases. Typically the range of values for resistor R12 is from

50K

Ω to 150KΩ..

9

POWER-ON INPUT

A low level on this pin forces the external darlington into conduction

particularly useful in anti knock system. This function is particularly useful in

antiknock system because provides a spark time delay. Anyway the current

limitation,

the permanent conduction protection and the dump protection

are operating even when pin 9 is at a low level. If this function is not used it

must be left open.

10

SIGNAL GROUND

This pin must be connected to ground.

11

POWER SUPPLY

Supply Voltage Input. A 7V (typ) zener is present at the input. The external

resistor R9 limits the current through the zener for higher supply voltages.

12

DUMP PROTECTION

The device is protected against the load dump. In load dump condition an

internal circuit,

based on a zener diode and a darlington transistor,

switches off the external darlington and short circuits the supply.

By means of the external divider R8/R9 the protection threshold can be

changed and is given as first approximation by:

= 8.5







R8

+ R9

R9







(the resistor R9 value must be higher than 4K

Ω).

* this function is particularly useful in antiknock systeme because provides a spark time delay. anyway the current limitation, the pemanent con

duction protection and the dump protection are operating even when pin 9 is at a low level.

L484

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