External Power for Teensy Issue

[Triale2]

Hi there!

Im looking to power the Teensy3.1 externally. The power source is a 3.7 Lipo battery however it has been boosted,inverted and split in order to get +5V, -5V and 0V. The Teensy was plugged into the +5V and the 0V part of this power supply and I was also trying to drive a 3.3 V bluetooth module from the Teensy regulator. I cut the tracks to enable external power supply but the bluetooth module barely even blinks now. Im wondering if the load is too much for the battery or do I need to do something else? Any help appreciated!

 

[Constantin]

I'd consider a buck/boost power supply with a 3.3V output voltage that is attached to the 3.3V pins. Why go up to 5V only to come down again?

If you plan to use USB with this sort of setup, remember to cut the pad-pad VUSB-Vin connection on the underside of the Teensy so the voltage regulator inside the Teensy does not fight with your external power supply. You can still use VUSB as a power supply for your external power supply and/or battery charger. Simply route from the VUSB pin to their input(s) while being conscious of other power supply considerations (i.e. if you want to have room for an external power supply, you need to consider how VUSB and the xternal power supply can coexist happily, be it via a couple of Schottky diodes, a pin header, or the complicated approach the Arduino team took on their Uno board).

With an external power supply your Teensy K20 will run cooler (not a big deal but a feature), and your bluetooth power supply will likely benefit too from a external power supply that is right-sized for the job. I'd review the bluetooth module spec sheet to see what the maximum power draw is and chose the external power supply and decoupling capacitors accordingly. For example, one board I've designed uses two 470uF tantalum caps ($$$) with a SPX regulator since the GPRS module can pull 2A for milliseconds at a time while transmitting. Depending on the power draw and duration of your bluetooth module, you may need big capacitors (upstream and downstream from the regulator) to help deal with transients.