AN2334

Algorithms

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Algorithms

After turn on or resetting, the microcontroller initializes all used peripherals (I/Os, Timers,

ADC and LIN-SCI) and variables, drives the L9950 to open the left wing-mirror and sends a

LIN message to do the same for the right wing-mirror. Afterward, it starts an infinite loop that

can be stopped only by resetting or turning off the board.

The microcontroller starts polling on both key pins (for driving window lift) and the keypad.

As soon as a load is turned on, the L9950 Enable Bit is set to switch the device into active

mode, turning on the Charge Pump Output. This output drives the gate of an external n-

channel power MOS used for reverse polarity protection. This action, guaranteeing the

reverse battery protection, needs about 300µs, which is the activation delay for every load.

When no load is driven, the Enable Bit is cleared and the device goes into standby mode for

power saving.

It is possible to drive the window lift by using both the PC keypad and board keys (#4 / #5 -

Figure 9). The "Up key" and "Down key" pins are configured in the input pull-up mode, so

they are normally at a high value (5V); if the UP or DOWN buttons are pressed, two different

behaviors are shown, depending on the duration of the pressing time. If the button is

pressed for less than 100 ms, the glass moves up or down (depending on the key pressed)

until the top or bottom part of the window is reached; if the pressed time exceeds 100 ms,

the window moves up or down following the touch temporization. The same behavior occurs

when a PC software keypad is used.

The "Window Up switch" pin (#9 - Figure 9), also configured in input pull-up mode, must be

connected using a mechanical switch that senses the window end run, indicating that the

door upper limit has been reached.

The PWM 8-bit Autoreload Timer is used to perform a task temporized at 1 ms.

This task is in charge of all temporized events:

–

It counts 250 ms before sending a LIN request message to the dashboard

–

In case of window lift activation, it manages current sampling

–

It also controls the mirror folding, locking and turn indicator light on and off

switching timings

When either the Down or Up key (both in the board or on the PC keypad) are pressed, the

Window_Lift routine is called:

–

VNH2 InA and InB pins are, then, set or reset, depending on the key pressed, to

lift the window up or down and,

–

the 16-bit Timer is used to provide to the VNH2 a PWM signal with 20 kHz

frequency and 30% duty cycle

–

during a 1 ms task, the current sense voltage is acquired via ST7 ADC; the

acquisition is averaged over a 10 ms period to eliminate noise. Motor power is

calculated by multiplying the current sense by the estimated angular velocity. This

value is averaged over 100 ms, providing a delayed signal compared to the

original. The difference between power and averaged power must be compared

with a threshold to determine whether a pinch event occurs. This threshold

depends on the motor status (soft start up or steady state conditions).

Unless a Down/Up key is pressed or a pinch occurs, the duty cycle increases linearly until

100% is reached and the PWM becomes a constant (steady state phase, see Figure 2.)