Teensy on battery power with USB power when available

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Chevelle

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Hi. I have a project that I am working on and I looked up all the information I could find regarding how to run a Teensy on a battery but also having it run on USB power when available. I will be committing the design to having a PCB made so I would appreciate some feedback to be sure I have this right.

Here is my plan...

Since I will be using a battery, I will be cutting the USB-to-VIN jumper. The battery (3.7v lipo) will be coming coming into a switch, the output of which is "+3v3B" and will be used to power everything, including the Teensy buy connecting +3v3B to VBAT. The battery will also connect directly into the battery charger circuit (MCP73831). The Vdd input to the charger chip will be from the VUSB pin on the Teensy. There will be no connection to VIN.

So I think that's it. Your comments are appreciated.

FYI, about the project. It is a nifty little pocket pressure monitor. My company and a few of our collaborating companies regularly need to precisely measure pressures and vacuums, from fractions of a PSI up to about 5 PSI. The circuit connects three Honeywell differential pressure transducers to the Teensy 3.2 and uses the appropriate one depending on the pressure/vacuum level being read. When connected via USB, there is a companion program that takes the data stream and plots and logs the data. The module also has a battery and a 16x2 LCD display so it can read pressure and vacuum without the computer if necessary. I'm happy to share the design when I know it works.

Bob
 
I have an additional question. Since this will be running on a battery charger circuit, the maximum output of that will be 4.2V. Can the VBAT input to the Teensy 3.2 accept this?
 
Couple pointers on your project.
The MCP73831 will work but your plan has a big risk of under volting the battery which is bad for lion.
The Teensy 3.2 and LC both have integrated 3.3v regulators which can accept up to 5.5v. Feeding it straight from the battery will work but i would suggest an IC with built in under volt protection and USB charging like the BQ24232.
I mention the LC because you should consider it for this project. Its cheaper and has better power consumption.
 
Excellent feedback Jacky. I like the battery management aspects of the BQ24232 that you mentioned but the package type is very unfriendly to bench soldering, at least for these first few. I will do some looking into it but if you happen to know of an equivalent that is a bit more prototype friendly, please pass that on.

Thanks again.

Bob
 
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