Qi and USB Li Charger Flex Module

Charger system for Li batteries with fuel gauge. Works with Qi wireless or USB power source. For sale on Tindie.

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Charger system for Lithium Polymers and 4.2V Li-ions. Provides Qi wireless sourced charging with the addition of a Qi coil as well USB if connected to our USB BiPower OTG Flex Module.

The charger system contains two main circuits. The first is a circuit to provide either Qi wireless or USB power sources to the charging circuit. The second is the charging circuit for the Lithium battery. The charging circuit provides an optional USB OTG 5V boost and a variety of power output options from the battery.

This board is part of Fyber Labs Flex Module project. Flex Modules are small modular circuits for wearable applications.

The Qi and USB Li Charger Flex Modules is a charger for a wide range of single cell (4.2V) rechargeable batteries. Charging sources are obviously Qi wireless and USB. Charging by USB requires the VBUS input (provided by our USB BiPower Flex Modules). In addition to charging, the Flex Module manages and monitors battery output and depending on configuration, it can also provide Qi based power through VBUS.

The BQ24296 provides a 5V boost to VBUS from battery to negotiate USB On-The-Go (OTG) Host Negotiation Protocol (HNP) and Session request Protocol (SRP) protocols to charge or charge from external OTG devices. The protocol is negotiated by a USB OTG device such as the STM32F401 microcontroller or the optional MAX3353 on the USB BiPower OTG Flex Module.

The BQ24296 additional provides VSYS power which outputs 4.2V-3.5V from the battery. It boosts the battery voltage when it falls below 3.5V to provide a more consistent voltage and full discharge. VSYS is utilized by the USB BiPower OTG Flex Module to power its 3.3V output when USB VBUS is not available. PMID is also available which provides either the 5V input or the battery if no charger input power available.

The BQ51013B negotiates with a Qi transmitter to supply 5V to the BQ24296 charger at up to 1.5A through the VBUS input. A dual P-FET configuration controls VBUS input/output or Qi input. Priority between charging sources or even providing USB OTG is selectable through i2c control.

Included is a STC3115 fuel gauge that monitors both voltage and current. Discrete logic defaults allow the charger to operate autonomously, though it can be fully controlled through i2c. The BQ51013B enable pins and the BQ24296 OTG pin are managed by an i2c GPIO device the PCA9570GM.

LED indicators report Qi or VBUS input, charging, or error.

NOTE: Any Qi wireless charging coil should be separated with a ferrite shield material from a given PCB design (flexible or otherwise) and the battery. Otherwise damage to components or worse can happen. We may package a solution in the future that includes this board, the ferrite shield, alignment magnet, battery, and a 3D printed outside casing to wrap around it.

Any software related will be released under BSD or MIT license. SAAS or cloud based software will be AGPL.

Creative Commons License

  • 1 × BQ51013B Evaluation, Demonstration Kits, Boards and Modules / Evaluation Kits, Boards and Modules
  • 1 × BQ24296 Power Management ICs / Battery Management ICs
  • 1 × STC3115AIJT Power Management ICs / Power Supply Support
  • 1 × PCA9570GM Interface and IO ICs / Other Interface ICs
  • 1 × NC7WZ32 Logic ICs / Gates and Inverters

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  • Charger issues

    Chris Hamilton08/13/2015 at 11:13 0 comments

    So far I haven't had any replies back from TI. I have power supplied from VBUS entering the BQ24296, but I believe the fuel gauge logic is preventing charge mode. The design is just too complicated compared to using a TI fuel gauge, so that will be our next step.

  • Still working on new design

    Chris Hamilton07/19/2015 at 09:41 0 comments

    I have been testing this design and there are some weird situations. I had thought to sell this version, but I don't think it necessarily works. I'll be working on some changes to the logic driving it asap. Possibly, I will end up just setting the Qi charger priorities to a fixed mode and improving the fuel gauge layout.

  • ST NRND'ed the STC3115AIJT?

    Chris Hamilton04/11/2015 at 08:12 0 comments

    OK, so it looks like ST is pulling out of fuel gauges. Great... Well, honestly even though I loved the STC3115AIJT, I had done a bunch of work trying to fully integrate the chip in. Now I am looking at the BQ27531-G1 which works with a similar series of chargers and actually 'runs' the charger and filters uc requests. So maybe it will be the awesome default discrete does most things, i2c enables all features USB/Qi Charger I meant to make.

  • Testing

    Chris Hamilton04/04/2015 at 18:11 0 comments

    Yield is very low and required re-working. The spacing per component is cramped, but it is just too much solder paste for the amount of area. It takes approximately 30-40 minutes to complete one which effected the slump and workability with my new 4300LF paste wasn't holding up well either. I think I'll stick to SMD291SNL for more complicated boards (and in general). I am going to be testing the board, but it will be expensive to sell at this point. I will try to minimize the Qi wireless capacitor count as much as possible.

  • Design Complete

    Chris Hamilton02/10/2015 at 18:42 0 comments

    Initial design is off to OSHPark. This design is 4 layers, but kinda breaks the rules in having what is essentially 3 signal layers. The ground plane is solid, but there are many high current traces, so they are actually placed on the bottom layer instead of a split internal VCC layer. This allows the design to be functional and fit within the 4 layer stack for OSHPark. The analog ground is somewhat isolated, though there may be issues with some near traces. The inductor is well isolated from traces.

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