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Thread: 3.3 volt teensy how to acheve more amps

  1. #1
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    3.3 volt teensy how to acheve more amps

    hi

    thanks for all the advice i have seen on the forum, i am using the teensy 3,6 for all my IOT projects (its a solid chip, and very well made) (just hope paull has enough stock ) would rather be overpowered.

    I intend at times using all the serial ports and SDA ports. now they all need 3,3 volts one pin wont supply enough power.

    If i connect say 2 of the 3.3-volt outputs to the same line would it double the amps or double the voltage to 6,6 volts. ?

    or shall i try a resistor divider off my 5V volt USB external line, if so can you recommend the values to bring USB power down to 3.3 with enough amps?

    your advice is much appreciated.

    thank you Gary J
    Last edited by GaryJ; 07-23-2019 at 06:02 AM. Reason: spelling

  2. #2
    Senior Member+ MichaelMeissner's Avatar
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    Both serial and i2c lines do not derive their power from the data pins. Instead they have a VCC, VIN, etc. line that provides the majority of the power to the device. The data pins just provide signaling.

    So if you hook up the Teensy's 3.3v line to the devices, you can typically draw about 250 millivolts from the 3.3v line (assuming you are powering the teensy with enough power to give you 250 milliamps after conversion from 5v). If you project budget within this parameter, then you don't have to do anything special.

    If you need more, then you need to design a better power strategy. If you need just a bit more than 250mA at 3.3v, you could grab the power from the USB line before it reaches the Teensy, and convert that voltage down the 3.3v , and hook that up your devices.

    If you need more, then you need to carefully design your power.

  3. #3
    Senior Member+ defragster's Avatar
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    Rest assured PJRC is working as needed to keep T_3.6's in stock Probably easier if you buy more keeping volume up

    Is the T_3.6 only powering its own Serial# ports - which draw power internally? Or is it powering other devices? External pullups through 2200 Ohm resistor if I read the calc right is only 1.5 mA

    Does the IOT use a radio Wifi or Bt? Powered from Teensy?

    All the 3.3V pins presented draw from the same supply - which has the spec limit of 250 mA. Marshalling more than one of those together won't give any added power and will still be 3.3V - though with lower quality connections like a breadboard I have seen can make up for single paths not providing full power.

    If there are external devices needing 3.3V then an external supply might be needed - but if 5V is from USB the current limit from the host would provide for limited added power when safely regulated - and if burned up in resistor divider would add half as much heat as power until the Host USB shut off for over current.

    That is hopefully generally right - more specifics for others to reply would need to know what is consuming power beyond the Teensy itself - like the Radio or GPS or Servo's or LEDs ...

  4. #4
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    Quote Originally Posted by defragster View Post
    Rest assured PJRC is working as needed to keep T_3.6's in stock Probably easier if you buy more keeping volume up

    Is the T_3.6 only powering its own Serial# ports - which draw power internally? Or is it powering other devices? External pullups through 2200 Ohm resistor if I read the calc right is only 1.5 mA

    Does the IOT use a radio Wifi or Bt? Powered from Teensy?

    All the 3.3V pins presented draw from the same supply - which has the spec limit of 250 mA. Marshalling more than one of those together won't give any added power and will still be 3.3V - though with lower quality connections like a breadboard I have seen can make up for single paths not providing full power.

    If there are external devices needing 3.3V then an external supply might be needed - but if 5V is from USB the current limit from the host would provide for limited added power when safely regulated - and if burned up in resistor divider would add half as much heat as power until the Host USB shut off for over current.

    That is hopefully generally right - more specifics for others to reply would need to know what is consuming power beyond the Teensy itself - like the Radio or GPS or Servo's or LEDs ...
    Thanks Guys, as recomended i am redesigning the power supply off the 5v line using the 3.3V 800mA Linear Voltage Regulator - LD1117-3.3 TO-220 from adafruit, that should give enough power, to run things ike Lidar ect off the 3.3 volt. I am running the devices off a USB power bank that thas a 2Amp output. (cheap batterys and you get a booster charger included. just strip them out. )

    I am running the particle electron as the Tranmitter and powering it with the USB as well just sharing a common ground and using Serial 4 to communicate, seems to work and quite Fast.

    thanks again Gary J

  5. #5
    Senior Member PaulStoffregen's Avatar
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    Yes, a regulator like LD1117-3.3 is a good choice if you have other 3.3V devices which need a lot of current.

    The 250 mA spec for Teensy's 3.3V output is somewhat conservative. As you can see on the schematic, the regulator on Teensy 3.6 is TI part LP38691. It's actually rated for more. We say only 250 mA as a guideline, because the MK66 chip on Teensy 3.6 also uses quite a bit of current, and the LP38691 does not have a heatsink. Ultimately the limit involves heating of that chip. If you do push things to the limit or slightly beyond, monitor the temperature in the center of your Teensy 3.6.

    Likewise, that LD1117-3.3 will get hot if you use a lot of current. Fortunately the TO-220 package is easier to connect to a heatsink or metal surface to dissipate the heat. Also pay attention to the note on Adafruit's page and in the datasheet, that a capacitor is required.

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