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high voltage on MCLR pin?

Discussion in 'Electronic Design' started by Tom Sam, Sep 22, 2007.

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  1. Tom Sam

    Tom Sam Guest

    Microchip gives a maximum voltage limit of about 13V on the MCLR pin of
    their Flash microcontrollers.
    But is there any kind of built-in limiter like a zener to protect the pin?
    All other pins (except the open drain one) got the classic diode protection
    to Vcc to protect the pin, as long as the current is limited to 25mA or so.
    The same question also apply to the open drain pin.

    Thanks in advance!

    Tom
     
  2. How the MCLR pin behaves, depends on the age of the chip. On older PIC's,
    this pin directly fed the programming circuitry. On latter chips, the pin
    is used as a reference, for the internal charge pump Vpp generator. In
    both cases, if the pin goes above the Vdd level, you risk erasure of the
    memory. The pin can also exhibit latch-up, if it drops below the Vss
    level. It does not have diode protection (in just the same was as the Vdd
    pins cannot have this...). However the current drawn rises fairly sharply
    at the programming voltage.
    RA4, does have the normal protection diode. This is mentioned normally as
    a small 'note' on the I/O pin schematic diagram.

    Best Wishes
     
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