AN3372 datasheet(24/37 Pages) STMICROELECTRONICS

24 / 37 page

ST7 microcontroller application pin use

AN3372

24/37

Doc ID 018625 Rev 1

Figure 16.

Half bridge ZCD circuitry

The buck circuit realized in the half bridge works in transition mode. To obtain this feature an

auxiliary winding is wound in the main inductor of the half bridge and when the current

reaches the zero value the variation of voltage is used by the PC0 pin of the microcontroller

to start the conduction of the power switches.

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Pin 23: not used

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Pin 24: HEI: MCU output used for igniter gate driver.

Figure 17.

Enable/disable igniter circuitry

Figure 16

shows that Q4 enables or disables the charge of capacitor C11. When the voltage

exceeds the voltage across D5, the discharge happens and in the primary winding the

generated high voltage ignites the lamp. The microcontroller generates a signal for the

L6382D5 that drives Q4. This pin is used also for microcontroller flash programming.

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Pin 25: PC3 this pin is used also for microcontroller flash programming

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Pin 26: LTIC PFC zero current detect.

AN3372 Datasheet(PDF) 24 Page - STMicroelectronics