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DETAILED DESCRIPTION

This is a Sandwich project battery charger module that can be used with any single 4.2V LiPo battery and can detect most of the currently existing USB chargers and charging ports and in case if dedicated charger is detected will switch to high current charge mode of 1A.

This module uses TI BQ24074 charger IC with PowerPath technology providing 4.4V Vsys voltage when USB power is connected or LiPo battery voltage if USB source is disconnected. Battery charging can occur in two modes - USB500 or 1A dedicated charger mode. In order to detect what type of charger is connected a TI BQ24392 IC is used. If dedicated charger is detected then BQ24074 is allowed to use current up to 1A to charge battery, otherwise if USB port is detected - BQ24074 is limited to 500mA of current to charge battery while still providing up to 1.5A of total power for system and battery charging. BQ24392 also has a USB2.0 internal switch so when charger detected to be a non-dedicated charger (charging USB port) internal switch would open allowing to connect any device past BQ24392 to USB port.

BQ24074 allows to choose charge current, termination current and input current using a set of resistors. Termination current resistor can be omitted allowing BQ24074 to terminate charging at default termination rate. This IC allows system to take up to 1.5A of total current used for powering system and charging battery simultaneously. It's recommended to have at least 1% or better resistors for these contacts.

BQ24392 can detect most of USB2.0-compatible chargers or charging ports allowing BQ24074 to use either high current charging mode or USB100/USB500 modes. In my design USB500 mode and 1A high current charge modes are used.

After testing following results have been obtained:

When charging with 1A of current max of 66mV loss was measured between output of BQ24074 and battery positive terminal (reported by BQ27421), giving us RDs(on) of 66mOhm MAX after passing both MOSFETs and BQ27421 that has 7mOhm internal current sensing resistor. So, RDs(on) of each MOSFET is only 29.5 mOhm at 1A.
This board design allows BQ24074 to only reach approx 65-70C temperature when charging with designed 1A current.

If you have any questions regarding this project please don't hesitate to contact me over my email: y.kirsanov@gmail.com or here in comments.