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SN74AVCH8T245: Pull-up / pull-down resistors for bus-hols component

Ofer Eyni
Prodigy 40 points
Part Number: SN74AVCH8T245


Hello to the team,

Data-sheet of SN74AVCH8T245 recommends to avoid using pull-up/pull-down resistors for the inputs of the component.

However, the SCLA015 document (Application Report on bus-hold circuit) says the opposite: "Another way of ensuring a defined level during a bus’s inactive phase is by tying the lines to the supply voltage or to the ground potential via resistors" (in paragraph 4.2)

my questions:

1. Please clarify the contradiction.

2. what is the best way to ensure stable and known state of the outputs, while the inputs are in open state?

3. what is the best way to ensure stable and known state of the outputs, for an open/GND input ?

Thank you,

Ofer.

  • 0
    TI__Guru 62720 points
    Ofer,

    The application note paragraph 4.2 is actually leading to the fact that the bus hold circuits are needed and an acceptable solution when the bus lines are floating or Hi-Z.
    The paragraph assumes that the device connected in the lines are not bus hold devices.

    Using the bus hold device, it ensures that the input and output lines are held to the last known state through a weak latch internally.