AN2747 datasheet(24/44 Pages) STMICROELECTRONICS

24 / 44 page

ST7LITE39 microcontroller

AN2747

24/44

Figure 22.

Lamp voltage sensing circuit

Figure 23.

Lamp voltage measurement circuit

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Pin 7: PB3 digital floating input with interrupt. This pin is used for maximum current

protection.

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Pin 8: PB4 digital floating input. It is used for MCU Vref calibration.

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Pin 9: push-pull output, used to drive two status leds. A green LED indicates the normal

status. A red LED indicates a fault condition (for example overcurrent protection).

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Pin 10: SCI RXD, used for external communication, power line modem or PC

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Pin 11: SCI TXD, used for external communication, power line modem or PC

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Pin 12-13: PA6-PA5 not used

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Pin 14: PA4 output PWM3. It is used to generate a reference voltage for the constant

current control.

The current signal is obtained through a sense resistor R102 (ILAMP signal Figure 25). This

voltage across R102 is amplified by U4b STMicroelectronics amplifier TS272 and it is

compared using the comparator LM119 with the reference voltage coming from the MCU.

When the Ilamp signal exceeds the defined threshold, the comparator output falls, giving the

reset signal to the drivers.

AN2747 Datasheet(PDF) 24 Page - STMicroelectronics