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SN74LVTH244A: Replacement for SN74LV244A

Darren (FAE)
Expert 5483 points
Part Number: SN74LVTH244A
Other Parts Discussed in Thread: SN74LV244A, SN74HC244, SN74LVCH244A, SN74ALVCH244

Besides the operating voltage difference and characteristic ambient temperature, are there any other parameters you think are important, that are different between the two, for a P2P replacement?

Replacing SN74LV244A with SN74LVTH244A

What about SN74HC244?

  • 0
    TI__Guru* 96591 points

    Hi Darren,

    The key differences between LV244 and LVTH244 are that the "LVTH" device includes TTL-compatible (reduced threshold) inputs, and also bus-hold input circuits. While TTL-compatible inputs don't often cause any issues, the bus-hold circuits can cause some problems if the customer has any pull-up or pull-down resistors used external to the device, or if the inputs are being driven by weak signals (ie can't overdrive the bus-hold circuits).

    This app note discusses the issues surrounding bus-hold circuits at length: https://www.ti.com/lit/scla015

    HC244 has positive input clamp diodes, whereas the LV family does not.

    As for finding a replacement for the LV244, we would need some details to determine the best fit.

    Is this just a supply constraint issue, or is the customer seeing some kind of issue in their system with the LV244? (if there is an issue, what is it?)

    What's the supply voltage?

    Input signal?

    Output loading?

    Power supply sequence (relative to I/O signals)?

    Is there a requirement for the device to be in the high-impedance state with VCC = 0V?

    Is there a limitation on static power consumption?

  • 0 in reply to Emrys Maier
    TI__Expert 5483 points

    Hi Emrys,

    This is a supply issue for an RS-485 transceiver SN65HVD3088EDR, output of which is connected to one of the LV244A's inputs. 
    Because of supply issues, they are considering removing the RS-485 transceiver, in this case, one of the inputs to LV244A will float.
    They don't want to do board changes, so need a "bus-hold" P2P alternative to LV244A. (PW 20pin package)

    It looks like LVTH244 and LVCH244 are alternatives with parts, and same Enable structure / Pin assignment.

    VCC: 5V, but 3.3V is also acceptable

    I can confirm other Q's, but in the meantime:

    I understand difference between LV244A and LVTH244A

    Emrys Maier said:
    The key differences between LV244 and LVTH244 are that the "LVTH" device includes TTL-compatible (reduced threshold) inputs, and also bus-hold input circuits.

    Then what is the main difference between LV244A and LVCH244A?

    SN74ALVCH244PWR

  • 0 in reply to Darren (FAE)
    Guru 244220 points

    Please note that LV-A, LVT, LVC, and ALVC are different families.

    For 244 devices with bus hold, you have three choices: SN74LVCH244A, SN74ALVCH244, and SN74LVTH244A. (All of them support only 3.3 V.) The LVT device has higher drive strength, but much higher power consumption. ALVC has slightly lower propagation delay than LVC, which probably does not matter for you.