I have a simple circuit where 5V signal is fed into a buffer (Nexperia 74LVC1G07), then from the buffer into another device. The buffer is fed 5V by a switching DC-DC (R-78HB5.0-0.5/W). After it’s been off for a while, the buffer works, the signal is recognized by the receiver. This continues for some time, minutes, to tens of minutes. Then the buffer stops working. The DC-DC still works as well as the source. If I unplug it and let it sit for an hour, it resets back to working for a while until it stops.
Context:
The setup runs on an ebike 36V battery. Theres a hub motor connected to the same battery (via power controller). The signal source is a torque sensor. The destination is a bike computer.
Any idea what could be causing this? I don’t know much about electronics. I learn specific bits to do something but I’m ignorant otherwise. E.g. I know what a buffer does, I understand how it works on high level but I have no clue for example how it could be affected by the rest of the system electrically through noise, EMI, etc. My physics intuition here makes me think there must be some charge buildup happening which dissipates with time when turned off. I’ve no idea if this is remotely valid, or if it is how to fix it. Any ideas are appreciated!
If I had to guess, perhaps the buffer circuit is going onto latch-up due to ESD spikes, which is then locking the open drain to conduct, which is why you’re seeing a LOW output.
When in doubt, I suppose you can tack on more decoupling capacitors nearby the buffer’s Vcc.
As an idiot, do I wire capacitors in parallel to Vcc and GND of the buffer? What value?
Also I have the same kind of buffer from TI. Is there any sense to change the Nexperia IC and see if the TI fares better?
E: I read on decoupling capacitors. They go between Vcc and GND. The suggested general values I see from SparkFun are 0.1µF, 1µF and 10µF. Does that make sense?
Yes, sounds about right. For general purpose decoupling that is a good value. Make sure to place it as close to the IC as possible. A longer path will add more “noise” to the system. Do read more about the capacitor type too since it can matter a lot. I suggest looking at Phil’s Lab video on YouTube to learn more about this stuff