Best way to power a Teensy 4.1 and devices

KrisKasprzak

KrisKasprzak

Well-known member
All,

I'm in the process of redesigning a project, moving from a Teensy 3.2 to a 4.1. What is the best practice in powering a 4.1? I'm paranoid about overloading the onboard regulator as I have a bunch of sensors, display etc. drawing around 200 ma. I would really like to keep power supply external however the docs say to NOT apply input power to the 3v3 pin on the 4.1.

I do have a 5.0 buck dropping my source voltage from 24 VDC to power a few sensors, but not sure the best way to drop that to 3v3 (LD33, better buck, etc.) and power the 4.1?

How are 'yall powering your units?
 
If your 5V DC-DC converter is reasonably clean, it should work OK to power the Teensy 4.1. I run the Teensy 4.1 on most of my boards directly from a DC-DC converter.

It is always best to power the Teensy 4.1 using 5V on the VIN/5V pin or you can use USB. Don't mess with trying to power it from 3.3V directly or you can run into issues with how the power supplies sequence up. Paul takes care of all that when the 5V pin is used.

I then use that same 5V source to also power an external linear 3.3V regulator to power the external circuits. I am not a fan of using the Teensy onboard 3.3V regulator to power much of a load or if the load may have much capacitance on it or if you are not sure what you are going to be powering off of it over time which is the case with just about everything I design.

Teensy 4.1 are pretty tough, but the one failure mode you do see occasionally is the 3.3V regulator. Some design tradeoffs are made by the chip mfrs to make the dies small enough to fit into the very small packages necessarily used on Teensy 4.1.

For instance large amounts of capacitance can back feed into the regulator when power is turned off and damage it. That doesn't happen with external regulators that use larger dies with space for more protection circuits. In general large external regulators are more robust and they can also handle more power and take more abuse without complaining. It also removes the waste heat from the Teensy 4.1 module as well which can only help.

Since both the Teensy 4.1 and the external 3.3V regulator are both powered from the same 5V source, they will both power up and down together so you don't get into the possible issue of the Teensy 4.1 driving unpowered inputs or vice versa.
 
I also use 24 to 5V DC-DC to power Teensy and a GPS module.
On the Teensy, don't forget to cut the trace on bottom face and put a small diode on the pads.
Don't hesitate to put ferrites, 1nF, 10nF and/or 100nf capacitors (any combination) on the Traco converters outputs
 
I've used this sort of regulator quite successfully in the past to do what you want to do.
It's a complete solution on a mini-board, has all the Rs and Cs etc.
 
You can also use a low-dropout regulator down from 5V to 3.3V and save a more expensive DC-DC converter. The TracoPower devices are good, some have MTBF measured in 10's of millions of hours!
 
The ones I listed above are £0.39 (50c) each. I don't think you will beat that on price. See below.
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KenHahn said:
If your 5V DC-DC converter is reasonably clean, it should work OK to power the Teensy 4.1. I run the Teensy 4.1 on most of my boards directly from a DC-DC converter.

It is always best to power the Teensy 4.1 using 5V on the VIN/5V pin or you can use USB. Don't mess with trying to power it from 3.3V directly or you can run into issues with how the power supplies sequence up. Paul takes care of all that when the 5V pin is used.

I then use that same 5V source to also power an external linear 3.3V regulator to power the external circuits. I am not a fan of using the Teensy onboard 3.3V regulator to power much of a load or if the load may have much capacitance on it or if you are not sure what you are going to be powering off of it over time which is the case with just about everything I design.

Teensy 4.1 are pretty tough, but the one failure mode you do see occasionally is the 3.3V regulator. Some design tradeoffs are made by the chip mfrs to make the dies small enough to fit into the very small packages necessarily used on Teensy 4.1.

For instance large amounts of capacitance can back feed into the regulator when power is turned off and damage it. That doesn't happen with external regulators that use larger dies with space for more protection circuits. In general large external regulators are more robust and they can also handle more power and take more abuse without complaining. It also removes the waste heat from the Teensy 4.1 module as well which can only help.

Since both the Teensy 4.1 and the external 3.3V regulator are both powered from the same 5V source, they will both power up and down together so you don't get into the possible issue of the Teensy 4.1 driving unpowered inputs or vice versa.
Click to expand...
I'm working on something that only uses around 150mA but the capacitance problem seems to have tripped the regulator when i unplugged the battery. I need to have both options of powering it from usb or from a battery. Do you have any idea how I can modify this setup to allow for both modes. As in if i use an external 3.3v LDO is it ok for it to be powered from the 5v pin when using it with usb?
 
Yes, you can bring USB power in and run a 3.3V regulator off the 5V pin. Just keep in mind that the total current load can't exceed the 500mA or so of the USB port, but it sounds like you should be fine if you are just drawing 150mA from the 3.3V regulator.

If the Teensy is unmodified, you can power the setup from either the 5V pin using the battery or from USB but you cannot connect both at the same time or you will short the two power sources together. The one with the higher voltage will backflow current into the other power source. It won't hurt the Teensy, but could damage the USB port or battery.

If you want to be able to safely power the setup from either the 5V pin via the battery or from USB without worrying about shorting them together by connecting them at the same time, then you need to add some reverse current protection diodes to the circuit.

You do this by cutting the VUSB/5V traced on the bottom of the Teensy 4.1 and adding a reverse current protection diode across those pads with the cathode pointed toward the 5V pin as shown here.

1741019240039.jpeg


A similar diode also needs to be placed between your battery and the 5V pin also with the cathode pointed toward the 5V pin so you end up with the circuit below. This allows both power sources to be safely connected at the same time. The one with the higher voltage will power the Teensy as well as your 3.3V regulator that is hooked up to the Teensy VIN/5V pin. The one with the lower voltage will have the current blocked from flowing into it because that diode will be reverse biased.
1741018981469.png


Schottky diodes are typically used for this to minimize the voltage drop across the diodes, but in this application regular silicon diodes that can handle the current will also work fine.
 
KenHahn said:
Yes, you can bring USB power in and run a 3.3V regulator off the 5V pin. Just keep in mind that the total current load can't exceed the 500mA or so of the USB port, but it sounds like you should be fine if you are just drawing 150mA from the 3.3V regulator.

If the Teensy is unmodified, you can power the setup from either the 5V pin using the battery or from USB but you cannot connect both at the same time or you will short the two power sources together. The one with the higher voltage will backflow current into the other power source. It won't hurt the Teensy, but could damage the USB port or battery.

If you want to be able to safely power the setup from either the 5V pin via the battery or from USB without worrying about shorting them together by connecting them at the same time, then you need to add some reverse current protection diodes to the circuit.

You do this by cutting the VUSB/5V traced on the bottom of the Teensy 4.1 and adding a reverse current protection diode across those pads with the cathode pointed toward the 5V pin as shown here.

View attachment 37066

A similar diode also needs to be placed between your battery and the 5V pin also with the cathode pointed toward the 5V pin so you end up with the circuit below. This allows both power sources to be safely connected at the same time. The one with the higher voltage will power the Teensy as well as your 3.3V regulator that is hooked up to the Teensy VIN/5V pin. The one with the lower voltage will have the current blocked from flowing into it because that diode will be reverse biased.
View attachment 37065

Schottky diodes are typically used for this to minimize the voltage drop across the diodes, but in this application regular silicon diodes that can handle the current will also work fine.
Click to expand...
Thank you for the detailed response I really appreciate it!
One other thing, the gpio pins on the teensy shouldn't receive any input when the teensy is not powered on, since my external battery is supplying both my the teensy and the external components via the LDO regulator this shouldn't be a problem right? As in even though they are powered from a separate 3.3v line, it's fine because both the teensy and the external parts turn on/off at the same time.
 
That is correct. As long as both the Teensy and external 3.3V regulator are being powered from the same source, everything will power up and down together with no issues. All of my systems are setup this way. I never use the Teensy on-board regulator to power external 3.3V circuits.

I do have one circuit where it is possible for the Teensy to possibly try to drive unpowered inputs on an LCD and in that case, I use a bus switch IC to isolate those lines when the LCD does not have power applied to prevent the Teensy from trying to drive those inputs, but you shouldn't need to worry about that in your setup.
 
KenHahn said:
That is correct. As long as both the Teensy and external 3.3V regulator are being powered from the same source, everything will power up and down together with no issues. All of my systems are setup this way. I never use the Teensy on-board regulator to power external 3.3V circuits.

I do have one circuit where it is possible for the Teensy to possibly try to drive unpowered inputs on an LCD and in that case, I use a bus switch IC to isolate those lines when the LCD does not have power applied to prevent the Teensy from trying to drive those inputs, but you shouldn't need to worry about that in your setup.
Click to expand...
This is the circuit I've got for 4AA battery pack at 1.5V each. is this ok? :)
1741125878342.png
 
I think your circuit basically looks OK. It is important that the 5V to Teensy never exceed 5.5V or it will damage the Teensy. The silicon diode drop of approximately 0.7V should be enough if your battery never exceeds about 6V or you could put 2 diodes in series to drop closer to 1.4V to be on the safe side which is probably what I would do. The Teensy and regulator are both good down to below a 4V input.

I am not sure of the value of the Zener diode in this circuit. If the battery voltage goes high enough for it to conduct, it will be destroyed since there is no current limiter in the circuit. I don't typically use Zener diodes or battery power sources for that matter, so hopefully someone with more experience in this area can chime in.
 
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