DARLINGTON OVERVOLTAGE LIMITATION

The darlington is protected against overvoltage by

internal zener. This zener drives the external dar-

lington in order to limit the collector voltage.

CHARGING ANGLE SIGNAL OUTPUT

This signal is intended for tachometer applications

(pin 5). It consists of an open collector stage with

current internally limited at 10mA

"POWER ON" SIGNAL INPUT

In the low status this input forces the external dar-

lington into conduction (pin 9). This control input can

be used together with the conduction time informa-

tion coming from pin 5 to bypass the normal dwell

time calculation. When an external logic control is

used to recognize particular engine condition (as in

anti Knock system).

PROTECTION CIRCUITS

PERMANENT CONDUCTION PROTECTION

This function is intended to prevent continuous cur-

rent conduction in the final stage when the magnetic

pickup is open or intermittent. The duration of the in-

tervention is set by means of a capacitor 1 at pin 3.

Grounding pins 3 or 4, this protection is eliminated.

The inhibit function at pin 4 is particularly useful

when an external logic control is used to disable the

permanent conduction protection.

REVERSE BATTERY AND DUMP PROTECTION

vice is protected against reverse battery. The load

dump protection withstands up to 100V with a decay

time

≤ 300ms. The intervention threshold for load

dump is fixed by means of an external divider con-

nected to pin 11.

OTHER APPLICATION INFORMATION

If the supply is voltage 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.

The zener diode Dz, connected between pin 14 and

GND, allows to withstand positive spikes up to 200V.

The device - used in the recommended application

circuit - satisfies the ISO/DP 7637/1 overvoltage

standard.

Figure 1 : Typical Magnetic Pick–up Waveform and L484 Response at low and high

fequency.

L484

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