I’m powering my board constantly via VSYS pin and I need to sense whether a USB cable is connected.
This should be supported via GPIO 24. However, this IO is always HIGH because the schottkey diode that separates it from VSYS is probably faulty and VSYS voltage leaks into GPIO 24.
Is there a known issue with these boards and the BAT60A diodes?
I see this behavior on multiple boards I have.
Can you use scope to see what is going on the GPIO24 pin? It seems this circuit may be sensitive to impedance therefore ensure you do not activate any internal pull-ups/downs for the GPIO24 in the MCU (if there’re such ones).
I define GPIO 24 as input (no pulls) and I can measure over 4V on VBUS even though only VSYS is connected. So I assume D1 is faulty, is there any other explanation?
Your measurements were expected, because reverse current of BAT60A is 0.3 mA @ 5V, and in your case the current flowing through the resistors and diode is 0.25 mA. So I am curious if this circuit is ever expected to work at all by the design. There probably must have been a MOSFET.
We need comments and proof from the circuit designer and tester.
Now I see that the reverse leakage of the BAT60a is an order of magnitude greater than the MBR120VLSF diode used in the original pico (in which the GPIO24 functionality works as expected).
So I to fix my current boards I need to either replace the diode or lower the resistance of the voltage divider. Any other options?
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Make a change and report back on the results. Thanks!
I’ll replace the diode.
I’m planning to use this diode ZLLS410TA Diodes Incorporated | Discrete Semiconductor Products | DigiKey
any thoughts?
This one has less forward current and higher forward voltage. Must be within the W5500 power rating, but you must assess the whole board current level (including peak when it is turned on using USB) to ensure diode will not break down. For your test should be ok to see if situation improves.
