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pullup resistors value recommendation? — Parallax Forums

pullup resistors value recommendation?

henry99henry99 Posts: 67
edited 2009-07-23 01:52 in Propeller 1
I want to pull up resistors for the following scenarios:
1) to interface to CMOS open collector outputs (10khz range) pull up to 3.3V
2) to interface to TTL open collector logic (pull up high value to +5V)

Any suggestions on a value?· I've seen 1k or 4.7k as common.

Thanks!

Comments

  • Nick MuellerNick Mueller Posts: 815
    edited 2009-07-22 07:58
    > Any suggestions on a value? I've seen 1k or 4.7k as common.

    You can have anything between 1k to 10k or even 1M.
    It's just a question of speed and noise immunity.
    You'll always be on the save side if you look at how much current the device can sink/source and stay at about 30..50% of that.
    The rest is simple math: U = R * I


    Nick

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  • BigFootBigFoot Posts: 259
    edited 2009-07-23 01:49
    It is always a good idea to keep resistor values below 20K for noise reasons. I use
    10K for pull ups and 4.7K series resistors for 5V to Propeller input interface. The I2C
    signals are an exception, I use 2.2K pull ups for fast signal transitions.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-07-23 01:52
    Any pullup from a Prop pin to +5V will have to be 2.2K or greater. This is to accommodate the 500uA maximum forward current through the Prop's body diodes.

    -Phil
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