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L9524C-TR

Glow plug system control IC

STMicroelectronics 

L9524C

Functional description

4.14

Note:

Power regulation

The power through each glow plug (here expressed by VRMS which is the root-mean-square

voltage across one glow plug) depends on the battery voltage VBAT and the duty cycle tG

on/TG of the PWM signal applied to the external power MOSFET’s:

Equation 2

VRMS = VBAT ⋅

t--G------o---n-

TG

In order to regulate the power through the glow plugs the L9524C measures VBAT and

adjusts tG on/TG of the gate drivers (G1...4) such that VRMS = VRMS ref, where VRMS ref

represents the desired power through each glow plug.

The desired power VRMS ref is given by the input duty cycle tCI on/TCI which represents the

desired output duty cycle at a nominal battery voltage of 12V:

Equation 3

VRMS ref = 12V ⋅

-t-C----I---o---n-

tCI

As a result, the actual output duty cycle of the gate drivers is given by:

Equation 4

t--G------o---n-

TG

=

⎛

⎝

V--1---B-2---AV---T--⎠⎞

2

⋅

t--C----I---o---n-

TCI

The L9524C varies both the on time tG on and the period TG of the PWM output signal to

vary the duty cycle tG on/TG.

The accuracy of the power regulation is given by ΔVRMS = VRMS - VRMS ref.

The output jitter (electrical characteristics Item 8.8) is not taken in considuration while the

average is zero over some periodes.

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