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L9524C-TR

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27
L9524C Functional description
19/27
4.9 Relay output
In relay mode (modes 1 and 2) the IO pin is used as output pin to control an external relay
driver (e.g. a low-side switch which drives the relay). If the output stage of the IO pin is
switched on it behaves like a voltage source (V
IO
) with output resistance R
IO
. If it is switched
off a pull-down current source is activated (I
IO
). The relay output suppresses pulses shorter
than t
IO sup
such that the relay can be permanently switched by applying appropriate PWM
signals to the CI pin (see section “Control input”).
In transistor mode (modes 3 to 6) the IO pin is used as input pin. Left open it is pulled down
to ground and the power regulation feature (see section “Power regulation”) is activated
(V
IO
<V
IO pr
). To deactivate the power regulation feature the IO pin must be connected to
the CUR pin (V
IO
= V
CUR
> V
IO pr
).
4.10 Gate charge/discharge current variation
The CUR pin provides a constant current-limited output voltage V
CUR
. The gate charge (or
discharge) current is a multiple of the current flowing out of the CUR pin and can therefore
be varied by applying a resistor to the CUR pin.
In order to select the mode of operation the IO pin and/or the MS pin may be connected to
the CUR pin (see section “Modes”). The IO pin contains a pull-down current source and the
MS pin contains a pull-up current source. These currents are compensated if the
corresponding pin is connected to the CUR pin in order not to affect the gate
charge/discharge current.
4.11 Overcurrent threshold variation
The overcurrent threshold V
OC
can be varied by connecting the OCT pin to an external
resistive voltage divider between CUR pin and ground. If the OCT pin is left open it is pulled
up to an internal supply voltage by a current source and a default value is used for the
overcurrent threshold. This default value corresponds to the condition: V
OCT
= V
CUR
/6. In
order not to de tune the voltage divider the pull-up current I
OCT
source is deactivated when
any glow plug is switched on.
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 t
del
. 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 t
gap
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 t
sup
after switching) are suppressed in all modes.
Figure 9. Output timing
L9524C Functional description
21/27
4.14 Power regulation
The power through each glow plug (here expressed by V
RMS
which is the root-mean-square
voltage across one glow plug) depends on the battery voltage V
BAT
and the duty cycle t
G
on
/T
G
of the PWM signal applied to the external power MOSFET’s:
Equation 2
In order to regulate the power through the glow plugs the L9524C measures V
BAT
and
adjusts t
G on
/T
G
of the gate drivers (G1...4) such that V
RMS
= V
RMS ref
, where V
RMS ref
represents the desired power through each glow plug.
The desired power V
RMS ref
is given by the input duty cycle t
CI on
/T
CI
which represents the
desired output duty cycle at a nominal battery voltage of 12V:
Equation 3
As a result, the actual output duty cycle of the gate drivers is given by:
Equation 4
Note: The L9524C varies both the on time t
G on
and the period T
G
of the PWM output signal to
vary the duty cycle t
G on
/T
G
.
The accuracy of the power regulation is given by
V
RMS
= V
RMS
- V
RMS ref
.
The output jitter (electrical characteristics Item 8.8) is not taken in considuration while the
average is zero over some periodes.
V
RMS ref
12V
t
CI on
t
CI
------------- -=
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27

L9524C-TR

Mfr. #:
Buy L9524C-TR
Manufacturer:
STMicroelectronics
Description:
Linear Voltage Regulators Glow Plug System Control IC Six
Lifecycle:
New from this manufacturer.
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