DESATURATION TIMES IN LOW AND HIGH FRE-

QUENCY OPERATION.Due to the upper limit of the

voltage range of pin 3, if the components of fig. 3, 4

are used, below 10Hz (300RPM for a 4 cylinder en-

gine) the OFF time reaches its maximum value

(about50ms) and then the circuit graduallyloses the

control of the dwell angle because D = T – 50ms

Over 200Hz (6000RPM for a 4 cylinder engine) the

available time for the conduction is less than 3.5ms.

If the used coil is 6mH, 6A, the OFF time is reduced

to zero and the circuit loses the dwell angle control.

TRANSIENT RESPONSE. The ignition system

must deliver constant energy even during the con-

dition of acceleration and deceleration of the motor

below 80Hz/s. These conditions can be simulated

by means of a signal generator with a linearly mo-

dulated frequency between 1Hz and 200Hz (this

correspondsto a change between 30 and 6000RPM

for a 4 cylinders engine.

CURRENT LIMIT. The current in the coil is monito-

nal comparator threshold value the feedbackloop is

external darlington in the active region. In this con-

dition :

added :

Icpeak (A)

=

(

+ 1)

PROTECTION CIRCUIT

PERMANENT CONDUCTION PROTECTION

The battery voltage is applied to ignition module by

means of the ignition key. In these conditions, with

the motor stopped, it is necessary that there is no

permanent conduction in the ignition coil irrespecti-

ve of the polarity of the input signal.

The L482 incorporates a timing circuit to implement

this protection ; the duration of the intervention is set

µF, and

Ω, when the input signal is high for more

than 1 s, the coil current gradually decreases down

to zero to avoid spurious sparks (see fig. 2).

This timing allows normal operation of the module

above 30RPM.

DARLINGTON OVERVOLTAGE LIMITATION

The darlington is protected against overvoltage by

internal zener. This zener drives the external darlin-

gton in order to limit the collector voltage.

REVERSE BATTERY PRTOTECTION. Due to the

presence of external impedance at pin 5, 10, 11, 14,

15, L482 is protected against reverse battery volt-

age.

DUMP PROTECTION.

The load dump protection withstands up to 100V

with a decay time

≤ 300ms. The intervention thre-

shold for load dump is fixed by means of an external

divider connected to pin 11 (DIP-16 package ver-

sion) or to pin 10 using a Micropackage type.

NEGATIVE SPIKE PROTECTION.If correct opera-

tion is requested also during short negative spikes,

USE OF THE IC ELECTRONIC ADVANCE SY-

STEM

When the device is digitally controlled the control

unit transmits a suitable input signal to the power

module, receiving in turn information that allows the

control of the dwell and the on time of the final tran-

sistor.

For this reason L482 provides the following outputs:

.

a time signal equal to the time in which the final

Darlington is in the active region i.e. when the coil

signal must be TTL compatible.

.

a TTL compatible output from the timing circuit

the DIP-16 package version is present after the

protection against cranking transients.

.

a time signal equal to the time in which the final

current flows through the coil, see fig. 1.

OTHER APPLICATION INFORMATION

If the supply voltage is disconnected - or the battery

wire is broken - while the current is flowing through

from recirculating into the device : in this way both

device and darlington are protected.

L482

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