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CD74HC238: Design guide

user5129062
Intellectual 295 points
Part Number: CD74HC238
Other Parts Discussed in Thread: SN74LS11

I have a question about CD74HC238 and 74LS11

1）CD74HC238：Whether the output port does not need to be suspended？Whether VCC need  add current limiting resistance？

2）74LS11:The input port connect ro MCU，how to ensure that the input is low level when the MCU is not configured？add pull low resistor？

  • 0
    TI__Guru* 96712 points

    Hi,

    I need to clarify some information before I can help.

    1）CD74HC238：Whether the output port does not need to be suspended？Whether VCC need  add current limiting resistance？

    What does "suspended" mean?  I have never heard this term in relation to an IC's outputs.

    The output is a standard CMOS push-pull output that has a recommended current drive of 4mA -- it does not have any internal limiting circuitry, so it's fairly easy to drive more current than we recommend from the output.  The Abs Max table lists 25mA per pin as the absolute most current they can handle.

    2）74LS11:The input port connect ro MCU，how to ensure that the input is low level when the MCU is not configured？add pull low resistor？

    The 74LS11 is not a TI device, however I will assume you're talking about the SN74LS11.

    If an input is not being driven high or low, you can add a reisistor (10kohm) from the input to ground to ensure that it is held low.