Adafruit LiIon or LiPoly Charger BFF User Manual

Adafruit LiIon or LiPoly Charger BFF Add-

On for QT Py

Created by Kattni Rembor

https://learn.adafruit.com/adafruit-qt-py-charger-bff

Last updated on 2022-04-12 02:26:29 PM EDT

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Table of Contents

Overview

Pinouts

• Power Slide Switch

• Battery JST Connector

• Charge LED

• Battery Monitor Pin and Jumper

• Charge Chip and Voltage Divider

Downloads

• Files

• Schematic and Fab Print

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Overview

Is your QT Py all alone(https://adafru.it/Zzb), lacking a friend to travel the wide world

with? When you were a kid you may have learned about the "buddy" system. Well, this

product is kinda like that! A board that will watch your QT Py's back and give it the

power and support to wander out past your USB port.

This little lipo charger is designed to fit onto the back of any QT Py board, and make it

easy for portable powering. Simply plug any standard 3.7V/4.2V lithium polymer or

lithium-ion rechargeable battery into the JST plug on the end. When powered by the

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USB port on the QT Py, the charger kicks in and will charge up the battery at 200mA

max rate. You'll see the yellow LED light up when that happens.

When the USB is removed, the battery will reverse charge into the 5V port via a

Schottky diode. You can turn it on or off with the built in slide switch as well.

A simple voltage divider on the cathode side of the diode and connected to pin A2

will let your firmware detect basic modes: if the voltage is over 4.3V, it is probably

plugged into USB. If the voltage is 4.2V or below its probably running on the Lipoly

battery and you can roughly determine the battery state.

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We include some header that you can solder to your QT Py. You can also pick up an

Itsy Bitsy short female header kit to make it removable but compact(https://adafru.it/

Zzc), you'll just need to trim down the headers to 7 pins long.

For use with Adafruit LiPoly/LiIon batteries only! Other batteries may have different

voltage, chemistry, polarity, or pinout.

Comes as an assembled and tested PCB

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Uses the 5V input via USB Type-C connector on QT Py

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For charging single Lithium Ion/Lithium Polymer 3.7/4.2v batteries (not for older

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3.6/4.1v cells)

200mA charge current

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Batteries(http://adafru.it/258) and QT Py are not included.

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Pinouts

This QT Py BFF has a bunch of features packed into a cute little board. This page will

explain the hardware!

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Power Slide Switch

Battery JST Connector

The power slide switch, located in the

middle of the right side of the board, turns

the BFF on or off, but only when the QT Py

is NOT plugged into USB power.

The battery JST connector, located in the

Charge LED

middle of the left side of the board,

enables you to plug in any standard 3.7V/

4.2V lithium polymer or lithium-ion

rechargeable battery to the BFF.

For use with Adafruit LiPoly/LiIon batteries

only! Other batteries may have different

voltage, chemistry, polarity, or pinout.

The charge LED, located in the upper left

corner of the board, lights up when the

battery is charging. Charging occurs only

when the QT Py is plugged into USB

power.

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Battery Monitor Pin and Jumper

Pin A2, located to the left of center along

the top edge of the board, is connected to

the simple voltage divider, which will let

your firmware detect basic modes. It

measure the 5V line which is after a

schottkey diode. If the voltage is over

4.0V, it is probably plugged into USB. If the

voltage is 3.9V or below, its probably

running on the Lipoly battery and you can

roughly determine the battery state.

There are a pair of jumper pads, located to the right of center, below the pins along

the top edge. These pads are connected to pin A2, between the pin and the voltage

divider. In the event that you want to use pin A2 for something other than battery

monitoring, you can cut the trace between these pads to disable monitoring on pin

A2. Solder the pads back together to enable monitoring again.

Charge Chip and Voltage Divider

The MCP73831 lipo charge chip, located

near the center of the board, will charge

up the battery at 200mA max rate.

Charging occurs only while the QT Py is

plugged into USB, and will happen

regardless of the status of the slide switch.

When the chip is charging a battery, the

charge LED will light up.

The voltage divider, located below A3 on the BFF silk, is connected between A2 and

5V via the cathode side of a diode. It allows for simple monitoring of voltage levels,

which can indicate whether the QT Py is running off USB, or being powered by a

battery plugged into the BFF.

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Downloads

Files

MCP73831 Datasheet(https://adafru.it/Zzd)

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EagleCAD PCB files on GitHub(https://adafru.it/Zze)

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Fritzing object in the Adafruit Fritzing Library(https://adafru.it/Zzf )

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Schematic and Fab Print

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