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SN74LS540: About output at power-on

Shuji Ishiwata
Mastermind 6335 points
Part Number: SN74LS540

Hi All,


I have a question about SN74LS540.


Is there a condition that the output becomes Hi-Z with G1 and G2 connected to GND?
Normally it will not be Hi-z.
Please tell me the conditions to become Hi-z.

Also, does the output temporarily become Hi-Z when the power is turned on?


Best Regards,
Ishiwata

  • 0
    TI__Guru* 96712 points

    Hello Ishiwata-san,

    This is the output circuit for the LS540:

    When the supply voltage (VCC) is less than the required bias voltage for any of the BJTs (approximately 0.5V), then the output will not be driven high or low and will be in the high-impedance state.

    Between 0.5V and 4.5V, the device is in a transitory state with some of the internal circuitry biased correctly, which can result in high, low, or high-impedance outputs. We do not define the state of the device between these values.

    Between 4.5V and 5.5V, the device will operate normally, depending on the input values provided for the output state.