Is PortB weak pull-out good enough for for units that requires pullout?


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  1. #1
    Member yvesmazzon's Avatar
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    Default Is PortB weak pull-out good enough for for units that requires pullout?

    Compliment of the season to all Picsters

    Is the PIC's week pull-out is good enough for unit like I2C memories or AD converter like the MCP3421 chip and others one wire like temperature converter DS18B20 ? If so it will save me at least 3 resistors to squeeze on my board. It seems to be working on Proteus simulator but will it work with real things?

    Regards,

    Yves

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    Default Re: Is PortB weak pull-out good enough for for units that requires pullout?

    Considering the standard values of resistors for i2c and one wire I suspect not. It might work in one set of circumstances but I'd look elsewhere to save component count ie LED with builtin current limit resistors.

    Also I suspect when the device is configured for hardware i2c it automatically turns off the weak pullup.
    George.

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    Default Re: Is PortB weak pull-out good enough for for units that requires pullout?

    Thank George,

    It is what I thought too. I never found any data of the equivalent ohms the weak pull-up is, I suppose I could find out by using incremental resistors and measure the voltage drop and calculate the DC impedance of the device.

    Cheers,

    Yves

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    Default Re: Is PortB weak pull-out good enough for for units that requires pullout?

    I seem to vaguely remember 100's of K's
    George.

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    Default Re: Is PortB weak pull-out good enough for for units that requires pullout?

    It depends on the device, but the weak pullup current is usually spec'd somewhere in the range of 25uA-300uA at 5V, so that's about 200K to 16K, with 38K given as the typical value.

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