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SN74LVTH373: Output has spike interference

zhang ping
Genius 3505 points
Part Number: SN74LVTH373

AD1 is the output of 373, and the input is normal. There is no downward or upward peak. Where the red and rose red boxes are circled, please help to see what the problem may be?

1. I try to connect a 100 Ω resistor in series with the AD1 output pin of 373;

2. I try to connect a 0.1uF capacitor to GND in parallel at the AD1 output pin of 373;

Are the above two methods helpful? Is there any other proposal?

lithium_mainboard_revc_e2300&e2.pdf

  • 0
    TI__Guru* 96802 points

    Hello,

    The SN74LVTH373 has 3-state outputs, so it's possible for it to be in the high, low, or high-impedance mode at the output. I see that you have OE\ tied permanently to ground, so actually in your case the output can only be in the high or low state.

    It looks like something else is turning on for a short time and trying to drive the line. Do you have more than one output driver connected to the same wire? I can see on the schematic that the "BOOT_A#" lines go from the '373 to the Boot ROM, but also to the CONN SOCKET 19x2 (J1). If something else is driving the line, it would explain the shown behavior.

    Another possibility would be a shift in the local supply or ground. This is generally less likely, however if you have large currents or magnetic fields somewhere on your board, this may also be a cause.

    I should note that if there is something else pulling the line high/low, then it is likely drawing a lot of current. To pull the 'high' state all the way down from 3.3 to 2.3V would require something around 32mA of current.