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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