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SN74LVC2G06: Pull Up Resistor Design Guide

Allan Fan
Expert 5720 points
Part Number: SN74LVC2G06

Team,

Customer is looking at open drain type solution SN74LVC2G06 for 0Vin to 5.5Vout/ 3.3Vin to 0Vout. May I check with you any guideline for the chosen of pull up resistor?

Thanks.

Allan 

  • 0 in reply to Allan Fan
    TI__Guru* 96591 points

    Hello Allan,

    Selecting a pull-up resistor is based on two primary concerns - speed and power.

    The smaller the pull-up resistor, the faster the edges will be, but the more power will be used.

    Larger pull-up resistors will use less power, but will result in slower edges.

    The equations that govern this are very basic:

    The power equation: P = IV

    Ohm's law: V = IR

    98% RC charge time: 4τ = 4RC

    Typically, engineers will use a pull-up resistor between 1kΩ and 10kΩ, but values are not limited to those.  If you get too small of a resistor, the current requirement can get too high for the device, and if you get too high of a resistor, the leakage current can start to become important.

    Two examples:

    A 1 Ω pull-up is obvously too small, as it would require 5A to operate at 5V

    A 10 MΩ pull-up is obviously too large, as even a 1 μA leakage current would cause a voltage drop of 10V.