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SN74AHCT00Q-Q1: Consideration of VOH value

Kaji@PAN
Mastermind 7015 points
Part Number: SN74AHCT00Q-Q1

Hi,

I am checking the VOH of SN74AHCT00Q-Q1.
I have two questions.

(1) There are specifications when IOH = -50uA and -8mA.
What is the VOH for -600 uA? Is there a calculation method?

(2) VOH is specified with VCC = 4.5 V.
When VCC = 5.0 V, should I consider it by multiplying by (5.0 / 4.5)?

Best Regards,

  • 0
    TI__Guru* 96591 points

    Hi,

    The -50 uA spec is intended for use when outputting into a high impedance load - VOH will typically be very close to  Vcc when operating this way (within 100mV)

    If you need to know the VOH limit at 600uA load, you can calculate the output impedance with the 8mA value, then use that to get the worst case drop at 600uA.

    The calculation is: Rout = (Vcc - VOH)/IOH = 0.56 / 0.008 = 70 ohms

    That means the expected drop at 600uA load is: 42 mV.  Since the datasheet spec at 50uA is 100mV, you can err on the side of caution and use the 100mV value instead.

    When Vcc is 5V, you would expect to see about the same voltage drop as that at 4.5V (4.5 is the -10% side of the 5V supply operation, ie worst case).

    So, if the voltage drop at 8mA load is 0.56V at 4.5V vcc, then you would expect to see that same drop (or less) at 5V, so 5V - 0.56V = 4.44V