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Adafruit Pro Trinket LiPoly/LiIon Backpack
Created by lady ada
Last updated on 2016-09-03 03:37:36 AM UTC
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Guide Contents
Guide Contents
Overview
Pinouts
Adjusting Current Rate
LEDs
Optional Switch
Downloads
Files & Datasheets
Schematic
© Adafruit Industries
https://learn.adafruit.com/adafruit-pro-trinket-lipoly-slash-liion-
backpack
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Overview
If you have a Pro Trinket you probably know it's the perfect little size for a portable project.
This LiPoly backpack makes it really easy to do! Instead of wiring 2 or 3 boards together to
make a charging system, this little PCB sits on top of the Pro Trinket and allows a
LiPoly/LiIon battery to plug in. When the Pro Trinket USB port is powered, the battery is
recharged automatically. Unplug the USB port and the Pro Trinket will switch over to the
rechargeable battery.
It does not work with normal Trinkets. However, you can use it with our Adafruit Sound FX
board series (http://adafru.it/rd9)!
© Adafruit Industries
https://learn.adafruit.com/adafruit-pro-trinket-lipoly-slash-liion-
backpack
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Ideally, this backpack is for use with the 3.3V Pro Trinket, so that the battery voltage (3.7V-
4.2V) will get regulated down to 3.3V on the Pro Trinket board. However, many times, you
can run a 5V Pro Trinket + accessories off of the ~4V from the LiPoly battery with no
problem. (Technically its overclocking but we've never seen that affect the Pro Trinket itself,
AVRs are happy to overclock without complaint).
© Adafruit Industries
https://learn.adafruit.com/adafruit-pro-trinket-lipoly-slash-liion-
backpack
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Solder the backpack on with the extra long header so that it can still plug into a breadboard,
or clip the long header leads short afterwards for a slim package. There are two LEDs - one
red and one green. While charging, the red LED is lit. When the battery is fully charged and
ready for use, the green LED turns on. Seriously, it could not get more easy.
© Adafruit Industries
https://learn.adafruit.com/adafruit-pro-trinket-lipoly-slash-liion-
backpack
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If you want to add an On/Off switch, we also made that really easy. The two 0.1" holes with
a box around them are the battery output line. Carefully cut the trace between them with a
hobby knife and replace with two wires from a switch like this slide
switch (http://adafru.it/drN), or this pushbutton one (http://adafru.it/1683), for example.
Charging is performed in three stages: first a preconditioning charge, then a constantcurrent fast charge and finally a constant-voltage trickle charge to keep the battery toppedup. The charge current is 100mA by default, so it will work with any size battery and USB
port. If you want you can easily change it over to 500mA mode by soldering closed the
jumper on the bottom, for when you'll only be charging batteries with 500mAh size or
larger.
© Adafruit Industries
https://learn.adafruit.com/adafruit-pro-trinket-lipoly-slash-liion-
backpack
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For use with Adafruit LiPoly/LiIon batteries only! Other batteries may have different
voltage, chemistry, polarity or pinout.
Comes assembled and tested
Uses the 5V input via Micro-B USB connector on the Pro Trinket
For charging single Lithium Ion/Lithium Polymer 3.7/4.2v batteries (not for older
3.6/4.1v cells)
100mA charge current, adjustable to 500mA by soldering a jumper closed
Batteries (http://adafru.it/258) not included.
© Adafruit Industries
https://learn.adafruit.com/adafruit-pro-trinket-lipoly-slash-liion-
backpack
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Pinouts
This little backpack is very "short & sweet" when it comes to pinouts:
5V - this is the pin that comes from the USB port power, with 5V DC to charge the
battery.
G - this is the common ground pin, shared with the battery and charger
BAT - this is the voltage out from the battery, which will range from 3.2V when the
battery is dead to 4.2V when it's charged.
Adjusting Current Rate
The default current rate is 100mA, which is safe for any battery 100mAh or greater
capacity. If you're going to be using larger batteries, you may want to bump up the charge
© Adafruit Industries
https://learn.adafruit.com/adafruit-pro-trinket-lipoly-slash-liion-
backpack
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rate for faster charging. Easy! Just solder the jumper on the bottom of the board as shown
here:
LEDs
There's two LEDs on the backpack
CHG red LED - This LED is lit when the battery is being charged.
DON green LED - this LED is lit when the battery is done being charged (charge
complete)
When the backpack is installed on the Pro Trinket, but not charging, you may notice these
LEDs faintly glowing. That's a side effect of a slight current leakage through one of the
protection diodes on the Pro Trinket. It's not harmful at all and you can basically ignore it.
Optional Switch
© Adafruit Industries
https://learn.adafruit.com/adafruit-pro-trinket-lipoly-slash-liion-
backpack
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If you want to have an on/off switch for your project, it's a quick mod. The line from the
battery to the VBAT pin has a 0.1" breakout with a thin trace in between. Cut the trace
between the two outlined pins and solder a switch in place. The switch is current-carrying
so make sure it can handle the current draw you're expecting
© Adafruit Industries
https://learn.adafruit.com/adafruit-pro-trinket-lipoly-slash-liion-
backpack
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Downloads
Files & Datasheets
Datasheet for the MCP73831 charger chip (http://adafru.it/dvn)
Fritzing object in Adafruit Fritzing Library (http://adafru.it/aP3)
EagleCAD PCB files on GitHub (http://adafru.it/pwD)
Schematic
© Adafruit Industries
https://learn.adafruit.com/adafruit-pro-trinket-lipoly-slash-liion-
backpack
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© Adafruit Industries Last Updated: 2016-09-03 03:37:35 AM UTC Page 12 of 12
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