Teensy 41 external 3v3 power supply

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RayanR

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Hy,

I am making a board where the 3V3 power usage exceeds 200mA. As such, I'm planning on adding a seperate 3V3 switching DC-DC converter in combination with the Vin 5V input.

However, i was wondering if i need to connect the 3v3 lines and how i should do this. I read that you could directly put 3V3in on the 3V3 outputs, but you need to change some stuff, so i'd like to not do it this way. I thought about using an enable signal to power up the external DC-DC converter. but i was wondering if i could safely connect the 3V3 output line of both the teensy and the external DC-DC converters

thnx,
RR
 
I would not recommend connecting the two 3.3V outputs together. Especially if the DC-DC converter is a modern design with a synchronous rectifier, that would end up with a pretty unsafe situation.

Probably the safest approach would be to keep the 3.3V power lines separate. Of course connect the grounds. If you use a 3.3V signal from Teensy to turn on the other power, then you know it can't be on until after Teensy's power turns on. Then the main safety issue is keeping any output signals from Teensy at logic low until you know the other circuitry is powered up. Well, unless you know the inputs on that circuitry is high impedance while power is off. Chips which don't specifically advertise that feature are almost always not safe to drive their inputs logic high until after the chip is powered. Teensy 4.1 is the same way - its pins should not be driven with signals until the 3.3V power is on.
 
well, guess i'll make sure every output is set to low, and have an input where i measure the 3.3V line of the DC-DC converter and halt my setup code until it is digitalRead(DCDC3V3) returns 1.

any recomendations on the switching frequency i should use?
 
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