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SN74LVCH8T245: Low impedance at start up eventhough I have added a pull up resistor between OE and VCCA

Mohamed Abdalla10
Prodigy 10 points
Part Number: SN74LVCH8T245

I am using beagle bone to control SN74LVCH8T245. Basically to level shift the beagle bone 3.3V input to 5V with more current capability.  The issue is, as soon as I plug power to my board I get a low impedance on pin 18/U14 (this is the only pin I care about and it is the only one I have measured with an oscilloscope) for 400ns this screws up my signal. 

Attached my schematic for this part for better illustration. 

How do I get rid of this problem on startup?

  • 0
    TI__Guru 62050 points
    Hi,

    Welcome to e2e.
    Is there a scopeshot on what you are observing?
    The 'H' in the device indicates that the device has bus hold circuitry. The bus hold assumes a default state, usually low at the start.
    also, when oscilloscope is connected, the weak pulldown from the scope probe is enough to output a low state. Is this what you are seeing?