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SN74LVC244A: About high impedance output status of SN74LVC244A

user5192011
Prodigy 10 points
Part Number: SN74LVC244A
Other Parts Discussed in Thread: SN74LVCH244A

Hello, in a massive product PCBA, we found some error when we used SN74LVC244APW to replaced SN74LVC244ADB (we used one compliant PCB pads to both 2 package).

We do the trouble-shooting and found there is a hardware design bug that the output have NO pull-down resistors, so when the /EN is high voltage level the output is sensitive to noise.

But we found that if we change SN74LVC244APW back to SN74LVC244ADB, then it can become OK.

We would like to ask:

1. whether SN74LVC244APW and SN74LVC244ADB have different chip die? or manufacture batch? cause thie difference.

2. If there is any pin-to-pin package chip to replace the SN74LVC244, which do not have high-impedance output(for example-bus hold) characteristics when /EN is high voltage level.

  • 0
    TI__Genius 16735 points
    Hello,

    1. Yes both the SN74LVC244APW and the SN74LVC244ADB are different. The SN74LVC244APW comes with a PW packaging while the SN74LVC244ADB comes with DB package type. You can find both these package drawings in the datasheet.

    2. I believe the device you are looking for is SN74LVCH244A where the H signifies the bus hold feature. Here is an appnote on the over view of bus hold circuitry: www.ti.com/.../scla015b.pdf

    Thanks!
    -Karan