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SN74AHC245: Vin(signal) operating voltage

Part Number: SN74AHC245
Other Parts Discussed in Thread: SN74AHC541

Hi Team,

In datasheet, I only find the recommended operating voltage(OE/DIR) is 0-5.5?

May I know the recommended operating Vin(signal)? 0V-7V? or it's the same as 0-5.5 like OE/DIR?

Roy 

  • Hey Roy,

    Looking at an older version of the datasheet it looks like the recommended input voltage will be 0 - Vcc. Looks like the spec got condensed down to just the output voltage since the I/O pins include the output. The outputs have the exposed positive diode so Vcc will be the max recommended. 

    Thanks,
    Rami

  • Hi Rami,

    But I think Vin could higher than Vcc because this is the AHC part feature. I don't think the Vin recommended operating Vin condition is 0-Vcc.

    Roy

  • AHC input buffers indeed are overvoltage tolerant.

    However, in this device, every I/O pin is connected to both an input buffer and an output buffer, and the output buffer is not overvoltage tolerant.

    If you need to be able to use higher input voltages, you must use a unidirectional buffer like the SN74AHC541.

  • Hi Ladisch,

    Okay. I think I may clarify my question. We just need to know the recommended operating voltage on every input signal pin.

    I don't think that the range is 0-Vcc because as you said that the AHC input buffers indeed are overvoltage tolerant. So I think that the input pin range is the same as absolute max ratings 0-7V.

    If you don't think so, maybe the suggested input signal range is 0-5V. I think it's ok to me, but I couldn't accept that the range is 0-Vcc.

    In our application, our signal may over the Vcc so we select the AHC part. If this is not recommended, may you let me know your suggestion?

    Thanks.

    Regards,

    Roy 

  • Roy,

    I agree with you in that the 0-Vcc contradicts the datasheet. The data sheets states : "The inputs can accept voltages to 5.5 V at any valid VCC making it ideal for down translation" and "Inputs are overvoltage tolerant allowing them to go as high as 5.5 V at any valid VCC" so I would say the recommendation looks to be 0 to 5.5V. 
    0-7V is the abs max though and would not be the recommendation.

    Rami

  • Hi Rami,

    So I think we may suggest our user the recommended operating Vin(signal) range following below spec. Is is ok?

    Roy

  • Yes, this is ok

    Thanks,
    Rami