To have a very short off time when the L584 input

goes LOW, an internal zener is available on pin 16.

This zener is used with an external divider, R8, R9,

as shown in figure 2. Suitable values can be found

from :

R9 + R8

V

R8

is 47V if the pin 8 is used for slow recirculation as in

fig. 2).

To ensure stability, a small capacitor (about 200pF)

must be connected between the base and collector

of Q2 when pin 16 is used.

A different opportunityfor a fast off time is based on

the use of the external zener diode Dz. In this case

also the maximum Dz voltage value is 47V.

LOAD DUMP PROTECTION

To protect the device against the positive load dump

(see application circuit) to avoid that pin 8 voltage

R

guaranteeing Q1 operation is given by :

= R6 



Ip

(+2)







(typ) even if the system correct operation is com-

pletely guaranteed.

The L584 application circuit suggested in these

notes allows the use of inductive loads with the low-

est possible series resistance (compatible with con-

structional requirements) and therefore reduces no-

tably the power dissipation.

For example, an electronic injector driven from

14.4V which draws 2.4A has a series resistance of

6

Ω and dissipates34.56W. Using this circuit a injec-

tor with a 1

Ω series resistance can be used and the

power dissipation is :

Ω

≅ 1V

≅ 1V

Ω

σ = duty cycle = 20%

therefore :

Pd

≅ 5.76 + 1.92 + 0.48 + 0.21 = 8.37W

This given two advantages : the size (and cost) of

the injector is reduced and the drive current is re-

duced from 2.4A to about 0.4A.

The applicationcircuit of figure 9 is very similar to fig-

ure 2 except that it shows the use of two supplies :

one for the control circuit, one for the power stage.

L584

10/13