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SN74AHC1G09: Can I design the circuit below (Vcc=3.3V, but pullup resistor to 5V)?

CHIHHSUAN CHOU
Prodigy 60 points
Part Number: SN74AHC1G09

Question 1 : 

The Absolute Maximum Ratings shows Vo=Vcc+0.7V (Max)

It's means 7V+0.7V? or Vcc is typical use Vcc? (ex If use Vcc=3.3V, Vo=3.3+0.7?)

Question 2 :

The Recommended Operating Conditions shows Vo=5.5V (Max)

It's means in any condition, as long as it is less than 5.5v?

(Even Vcc=3.3V,  but pullup resistor to 5V)

Question3 : 

Can I design the circuit below (Vcc=3.3V,  but pullup resistor to 5V)?

There are two ways to explain

1. Vcc=3.3V, then VOH=5V <The Recommended Operating Conditions shows Vo=5.5V (Max).-->OK

2. Vcc=3.3V, then VOH=5V > The Absolute Maximum Ratings shows Vo=Vcc+0.7V=3.3+0.7=4V-->NG

  • +1
    Guru 272490 points

    This is an error in the datasheet; the two VO entries contradict each other.

    In general, open-drain outputs do not have a clamping diode to VCC and allow voltages above VCC. The pull-up to 5 V should be fine.

  • 0 in reply to Clemens Ladisch
    Prodigy 60 points

    Hi 

    Thanks for the reply.

    In general, open-drain outputs do not have a clamping diode to VCC and allow voltages above VCC.

    -->Yes, that's what I understand in the past.

    Is  IC pin's voltage can't over the IC 's Vcc.?

    In this condition : Vcc=3.3V,  but pullup resistor to 5V.-->Vcc=3.3V, then VOH=5V >Vcc

    Is any TI  technical documents that I can refer to? About open-drain use condition.

  • +1 in reply to CHIHHSUAN CHOU
    Guru 272490 points

    The recommended operating conditions allow this. The entry in the absolute maximum ratings is wrong (and the offset of 0.7 V also would be wrong; the worst-case forward voltage of a diode would be 0.5 V or smaller).