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Original question:

SN74LVC1G00: SN74LVC1G00MDBVREP replacement for 74V1T03STR

SN74AHCT1G00: SN74AHCT1G00

Subramaniam NS
Prodigy 195 points
Part Number: SN74AHCT1G00
Other Parts Discussed in Thread: SN74LVC1G38,

Hi,

While searching for alternate for 74V1T03STR I could come across the closest alternate is SN74AHCT1G00DBVR. Whereas I looking for an open drain type output NAND gate. Can you please respond an open drain equivalent to SN74AHCT1G00DBVR. I suppose the ordering part will be SN74AHCT1G03DBVR for the device. Please confirm the availability for the same.

The alternate has to be mounted on production board.

Awaiting a sooner response.

Thanks and Regards,

Subramaniam

  • 0
    TI__Guru* 96591 points

    Hello Subramaniam,

    I did not find a TTL-compatible single NAND gate in the TI portfolio that also has an open-drain output.

    The closest matches I found were:

    SN74LVC1G38 - single 2-input NAND gate with open-drain outputs (not TTL-compatible)

    SN74AHCT1G00 - single 2-input TTL-compatible NAND gate (not open-drain)

    Do you know what the input signal to the 74V1T03STR looks like? What is the V_IH to the part?

  • 0 in reply to Emrys Maier
    Prodigy 195 points
    There are multiple of these 74V1T03STR . Input to 74V1T03STR are 5V logic inputs and few are TTL type. For the part 74V1T03STR VIH min is 2V, whereas I assume the inputs for the part ranges ~ 3.5V and above.
  • 0 in reply to Subramaniam NS
    TI__Guru* 96591 points
    It's not ideal, but the SN74LVC1G38 would most likely work for you if the inputs are above 3.5V. The official VIH value in the datasheet is 0.7*Vcc, so if your supply fluctuates up by 10% to 5.5V then your VIH value becomes 3.85V. The actual switching threshold is closer to Vcc/2, so I don't see any real problem with this from a switching standpoint.

    The bigger problem is with the power consumption -- if the inputs are that low, there will certainly be shoot-through current at the inputs that will likely be in the ~1mA range, which is far more power than these devices would typically consume given the correct inputs.

    I'd say to use SN74LVC1G38 if there aren't any other options available -- otherwise the board would have to be redesigned to support both a TTL compatible NAND and an open drain device after it.
  • 0 in reply to Emrys Maier
    Prodigy 195 points

    Hi,

    I understand certain inputs to the NAND Gate are being driven by IC operating at 3V.

    With your below inputs

    "The official VIH value in the datasheet is 0.7*Vcc, so if your supply fluctuates up by 10% to 5.5V then your VIH value becomes 3.85V. The actual switching threshold is closer to Vcc/2, so I don't see any real problem with this from a switching standpoint."

    I understand it will be ok to have the IC SN74LVC1G38  to translate the 3V logic with a pull up of 5V. In case the NAND IC is subjected to -40 deg C to 125 deg C of operation the logic translation will work. Please confirm.

    Thanks and Regards,

    Subramaniam

  • 0 in reply to Subramaniam NS
    TI__Guru* 96591 points
    Hey Subramaniam,
    This isn't something TI can guarantee -- it would be a risk you take to prevent adding cost for correctly updating your board design.

    The two problems are:

    (1) possibility of not switching below VIH (low risk, in my opinion)
    (2) possibility of damage to the device from excessive shoot-through current (moderate risk, in my opinion) due to the lowered input voltage.

    If it was my system, I would rev the board.