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Help identifying a SOT23 part

Discussion in 'Datasheets, Manuals and Component Identification' started by Virgo, Sep 12, 2017.

  1. Virgo

    Virgo

    2
    0
    Sep 12, 2017
    Hi,

    Can some one help me identify a SOT23 part on a sensor board?
    The Part has code AF4C on it and pin connections are as below.

    Pin1 is connected to Vcc(3.3V)
    Pin 2 is connected to a processor GPIO pin that can also be configured as ADC.
    Pin 3 is connected to ground.

    I was thinking this is a protection device, but realized that the pin 2 is connected only to processor pin, so guess it may be a voltage reference?
    Appreciate any help identifying this part.
    IMG_20170907_202807.jpg
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It could also be a voltage detector chip, but they're more common on the reset pin of a microcontroller.
     
  3. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Got any more details on the board, its schematic and/or its function?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    I've looked through my SMD codebooks and I can't find it.
     
  5. Virgo

    Virgo

    2
    0
    Sep 12, 2017
    @kellys_eye , The processor is STM32F072C8T6 (48LQFP) and the SOT23 pin2 is connected to Procesor pin 18 - Port PB0 that can also be used as ADC_in8.
     
  6. kellys_eye

    kellys_eye

    4,281
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    Jun 25, 2010
    That's the problem - if it was programmed as an input (ADC) port then it's possible it's a clamping zener to protect the input. If it was an output port I'd expect the SOT device to have a load resistor connected to Vcc in its collector (or in the emitter to ground) - indeed it would have a base current limiting resistor too. If there is no resistor to Vcc or a base resistor from the port pin then assume its a zener clamp diode.
     
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