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Std EditionLiPo Power Board

License: CC-BY-SA 3.0

Published Time:2019-01-27 01:56:17
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Description

LiPo Power Board is a power manager for your battery-powered product. Since the breakout format, it is intended for prototyping and development. It is designed for a single cell LiPo battery (3.7V) and to supply 2 voltages: a fixed 3.3V and a secondary adjustable output, able to deliver higher voltage and current. A physical switch allows you to cut out the voltage on both channels. USB-C and Jack connectors allow to recharge the battery.

The boost part is very flexible since you can just change the ratio between 2 resistors to change the voltage output. Moreover you can copy and paste it to get a third voltage output.

A typical application in which this board finds a perfect suit is where the MCU runs at 3.3V and sensors and actuators (such as LEDs WS2812B) requires higher and stable voltage.

Features

  • leakage current < 2uA (when OFF)

  • quiescent current < 800uA

  • maximum current on 3.3V channel: 500mA* (input 3.45V)

  • minimum current on 5V: 500mA (input 3.45V)

  • 5V output adjustable

  • maximum charge current 1A (default: 800mA)

  • voltage will drop to 3V

Main components

  • low dropout voltage regulator fixed to 3.3V, Microchip MCP1725
  • variable boost voltage regulator, Aerosemi MT3608
  • multisource recharger for single cell LiPo, Microchip MCP73837
  • ON/OFF switch
  • number of different connectors: USB-C; Jack Barrel connector; JST-PH (2.0mm, 2-pin); screw terminal (3.81mm pitched, 2 pins)

Usage

This circuit is designed to work with a battery always connected. For developing purpose, you may need to detach the battery. In this case, you may activate the LDO mode (available through USB-C only), shorting SEL2 and opening SEL1. Otherwise, in the default configuration (with battery) keep SEL2 open and SEL1 don't care.

Regulating maximum charge current and termination

R1 value regulates the maximum current to recharge the battery, according to the formula I(mA) = 1/R1(kΩ). Moreover, this resistor controls the termination charge. In particular, when the charge current falls below a minimum current threshold, the recharge process ends. The recharge threshold is a percentage of the maximum current established by the manufacturer. In general, when the maximum current is high, the threshold increases its value, leading to a lower recharge level. Hence, if you need to use all the available capacity, lower the maximum current. However, the default configuration will work for the majority of the cases (my experimental setup with max current 800mA and battery 400mAh, stops at 4.1V), so if you are not sure about what you are doing, ignore this note.

Pinout

The list of the pins and their functionality:

Pin Description
GND Ground
3.3V Regulated output at 3.3V
VBAT Unregulated battery voltage
5V Regulated output at 5V (adjustable)
PWR Output HIGH after 200us the 3.3V is stable, otherwise grounded
SON Set HIGH to activate the voltage regulators, LOW to turn off them. It is an alternative to the physical switch

Changelog

  • 1.0.0 ❌: first version
  • 1.1.0 ❌: resistors for USB-C; Resistors for LEDs Status; test pad for PG and THERM on MCP73837; Selector for LDO mode; PROG2 is now connected to Vdd to enable charge
  • 1.2.0 ⚠: fix usb-c CC2 wire; USB holes footprint shrinked; add screw terminal for battery; mosfet to cut 5V power path when button is off; PCB is 2mm wider; minimum track width is 0.2mm. The exported gerber has a minor issue with a track that create a short circuit, solvable with a Dremel.
  • 1.3.0 ❎: text height min 0.7mm; Resistors and Capacitor 0603 package; New Schottky Barrier Diode; Connect USB case to GND
  • 1.3.1 ⚠: fix PWR (power good) pin, improve readability of schematic, enlarged some tracks, (hopefully) last name change: LiPo Power Board
  • 1.4.0 ✅: fix missing GND of MT3608; add mounting holes; add header for an external on/off switch; remove useless resistor (R12); rounded corners
  • 2.0.0 ✅: transistor to handle 1A input on 5V channel; bigger anular ring for mounting holes; default max charge current lowered to 833mA; screw terminal 2.54mm -> 3.81mm; 3D model; min output guarantee current at 5V (tested@3.3V): >400mA
  • 3.0.0 ✅: MCP73837 MSOC -> DFN (thermal issue); Board shape (mounting holes); LEDs moved; NOTE for assembling: orientation marking of chip U1 is its ID

Notes about versions

  • EasyEDA doesn't let you switch among releases unless you have complete access to the project. If you have questions about old versions, drop me a message.
  • The real max charge current of versions 1.x and 2.x can be lower than programmer due to thermal limitation of MSOP version. If you really care about charge speed, you should look at DFN version, which has a thermal pad that improves heat dissipation. The max current may also be limited by the protection circuit of your battery.

Versioning conventions

Each printed board has a version. Version advancements are ruled accordingly to Semantic Versioning.

To show the status of each version I use the following symbols:

  • A White Heavy Check Mark (✅) means that it is successfully tested;
  • A Negative Squared Cross Mark (❎) means that it was almost successfully tested (the main functionalities are fine), but there are bugs affecting minor funcionalities;
  • A Warning Sign (⚠) means that the board is not usable out of the box but the bugs are fixable in DIY (decent) fashion;
  • A Cross Mark (❌) means that there are some problems that makes it unusable;
  • A White Question Mark Ornament (❔) means not tested.

Additional References

  • Application note AN1149 by Microchip, Designing A Li-Ion Battery Charger and Load Sharing System With Microchip’s Stand-Alone Li-Ion Battery Charge Management Controller. Useful to have a glace to implement proper battery management.
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