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SN74LVC1G66: The input voltage question for SN74LVC1G66

Part Number: SN74LVC1G66
Other Parts Discussed in Thread: SN74CB3Q3305

Hi team,

I want to use SN74LVC1G66. VCC is 3.3V.  The datasheet shows the I/O port voltage range is from 0 to VCC.

Q1:I want to confirm if the input voltage exceeds 3.3V, can the input pin be damaged?

Q2: From the datasheet, 6.1 Absolute Maximum Ratings shows the max switch I/O voltage is  (vcc+0.5)V, So, if the input voltage exceeds 3.3V+0.5v=3.8V, then the input voltage can be damaged, correct?

Q3: Can I use 5V input voltage when VCC is 3.3V?

Q4: If the input signal voltage is 3.3V, how to ensure the output voltage is also 3.3V, not have the voltage drop?

  • There are ESD protection diodes from GND to the I/O pins, and from the I/O pins to VCC. When you apply a voltage lower than GND or higher than VCC, the current through those diodes can get high enough to fry them. However, the absolute maximum ratings allow a diode current of up to 50 mA, so if you add a series resistor to limit the current (in your case, at least about 27 Ω), you will avoid damage.

    Table 6-5 says that the resistance is 20 Ω in the worst case. This resistance will result in a voltage drop, depending on the current. The only way to reduce the voltage drop is to reduce the current.

    It might be a better idea to use transimpedance amplifiers to convert the current to a buffered voltage signal before the switch.

  • I need an TI engineer to reply to me.
  • User4674678,

    The e2e forums are an excellent place to collaborate with other knowledgeable engineers around the world like Clemens.

    Only TI engineers can select the TI thinks resolved button and I selected this option to validate Clemens correct response.

    I see you have several threads on the forum in the past view days regarding switches. Are you using multiple switches in your system or are these questions trying to help you narrow down selecting the correct switch for your system?

    Do you have a diagram or schematic of what you are building to see if we can get you to the correct switch quickly?

    Thank you,
    Adam
  • Hi Adam,
    Thanks for your reply. I cannot upload my schematic since my company does not allow to share our shcematic.
    I need to use the switch in my circuit. Would you help me to confirm my above questions?
  • User4674678,

    Yes, I can confirm Clemens response to be accurate to address your questions.

    I can off a different switch recommendation to supplement Clemens answer.

    If you would like a device that can support input voltages greater than supply voltages you will need to look at devices with internal charge pumps to bias up the gate voltage of the internal pass FET. What do you think about the SN74CB3Q3305?

    Thank you,
    Adam