Hi All. I’ve searched the forum, but I haven’t found a solution to this problem.
I have a RT1062 board with a servo sheild V1 controlling 4 servos. The board connects and runs programs when connected to only the USBC port. The issue comes when I connect power to the VIN pin. As soon as I connect 5V to VIN (or any VCC pin on the servo board), the light on the RT1062 flashes red briefly and then rapidly flashes blue/green. The board then disconnects from USB, and will only reconnect if the board is completely powered down.
Oddly, this only happens when connected to some computers. Certain laptops work just fine and can command the servos (the light on the RT1062 remains solid green the whole time).
Yeah, this is happening because of the ideal diode on the V1 board. It turns off when switching between VIN and USB briefly for like 1us and in this time the voltage rail can collapse and cause the processor to crash if there’s a large load on 3.3V. There’s enough caps on the board to make sure this doesn’t happen if it’s not loaded with any logic on 3.3V though. The load from the servo controller logic is not too much.
One easy fix is to attach a lipo battery from like sparkfun. This 100% solves the problem by adding a bypass path to power the system when VIN changes in voltage. Lithium Ion Battery - 850mAh
Note that the RT1062 V5 solves this issue. It does not have these problems. Same for the upcoming N6.
What must be happening is that the 5V VIN sags because of the servos and goes below and above 5V multiple times quickly, causing the ideal diode to not select USB or VIN. You can also solve this by just raising the VIN voltage to like 5.5V which should give it priority and have enough clearance not to trigger a voltage switch to USB which is at 5V. This is the easist to do if you can change the VIN voltage.