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AN4460

SMED implementation

4.2

State description

The STEVAL-ILL057V1 demonstration board uses four independent SMEDs, one for each

LED string. All the SMEDs use the same configuration and share the same control

algorithm. This section describes a single SMED but the same principles are applied to all

the SMEDs. Figure 5 shows the SMED state evolution:

Figure 5. SMED state evolution

A state is defined by the Sx symbol while a transaction between two states is represented

by a line. A transaction is generated by an event, displayed as text on the line. The event

TIM_Cnt (x) is generated by the timer when it reaches the value configured in State x. An

event (line) represents an event generated by the input line. The inputs associated to

a SMED are defined in Section 4.1.

Each SMED has 3 associated events, marked as event (line) in Figure 5. Each event can

be: type Event_Seq or Event_Jmp. While Event_Seq events push the state machine to the

next sequential state, Event_Jmp allows the state machine to reach any state.

Each state is here described:



IDLE: initial state

This is the SMED initial state. The PWM line is set to 0 to keep the MOSFET OFF.

The next state is S(0) and it is automatically entered when the SMED starts. On

exit: clear timer AND set PWM to ON.



S(0): off-time

This state implements the FOT time and the output PWM line is set at 0 V. S(0)

enters the HOLD state when the SWx bit (event 2) is set to 0 or it goes to S(1) if

the timer reaches the FOT time. The SMED timer is cleared on exit.

Event_Jmp = Hold jump ON = event(2).

Event_Seq = TIM_Cnt.

On exit: clear timer AND set PWM to ON.

IDLE

HOLD

TIM_Cnt(2) OR

event(1)

TIM_Cnt(1)

TIM_Cnt(0)

event(1) - ON

event(2) - ON

event(2) - OFF

start

TIM_Cnt(3)

Interrupt on exit

AM16705v1

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