Functional description

L9524C

20/27

4.12

Advanced run-off control

In transistor mode (modes 3 to 6) the glow plugs are switched by an advanced run-off

control. The target is to minimize changes in the load current. Therefore, the PWM signals

applied to the glow plugs are phase-shifted to each other. There is a 5-step start-up

procedure at the beginning of a switching sequence. In step 1 the phase shift between the

glow plugs is set to a fixed value tdel. Therefore, all glow plugs are switched on once in the

first period of the PWM control input signal (CI) and are heated up quite simultaneously.

During the start-up procedure the phase shift becomes a value equal to the on time of one

glow plug. As a result, after the start-up procedure the glow plugs are switched on one after

the other to get minimal changes in the load current.

Figure 8.

Timing diagram of advanced run-off control

4.13

Output timing

In transistor mode (modes 3 to 6) there is a delay tgap between switching off one glow plug

and switching on the next one to avoid overlaps. Additionally, failures occurring during the

slope (i.e. in the time period tsup after switching) are suppressed in all modes.

Figure 9.

Output timing