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SN7406: function table

Part Number: SN7406
Other Parts Discussed in Thread: SN74LS06

The two ICs in questions are SN7406 and SN74LS06D.  They both claim to have a High-Level output voltage of 30 Volts, but according to the function table of the SN74LS06D a TTL low would be Hi-Z, not a high output.  Am I interpreting this wrong?  The SN7406 looks like the function table would be:

Input A

Output Y





 But I’m not sure if I’m misinterpreting the Y=Abar

On Page 8 of the SN74LS06D there’s the following function table.


The SN7406 has the following logic diagram on sheet 2.


  • Both the SN7406 and SN74LS06 have open-collector outputs:

    An open-collector output can never drive a high voltage, so the function table showing "Hi-Z" is correct.

    However, the most common thing you do with an open-collector output is to connect a pull-up resistor, so in practice, there will be a high voltage at the pin. The primary difference from a totem-pole output is that that high voltage is imposed by the external circuit, and can be different from the 5-V VCC.