If you’re looking to build a smart Battery charger/selector, then the PICREF-5 Reference Design, is going to make your task a lot easier now!

At the heart of the matter is a PIC16C73A microcontroller which handles all the hardware control and communications to meet both the SMBus Level 3 Smart Battery Charger Specification 1.0 and Smart Battery and Smart Battery Selector Specification 1.0. Bottom line: you have both, the Smart Battery Charger and Smart Battery Selector under single-chip control.

There is support for selection and charging of up to two independent battery packs. Many safety features such as thermistor monitoring is always available on both battery packs, regardless of the selected battery pack. Other safety features include PIC16C73A control selection of a single battery pack, so that the unselected battery cannot be active on the bus. This eliminates cross control and cross communication situations, which may lead to unexpected operation. As an added safety feature.

Immediate switching of the power source is implemented by use of three diode mode operation. If AC power or the active battery pack is removed from the system, there is no switch over time. The selector also supports end-of-discharge detection of the battery pack, so that switching to an alternate power source automatically takes place. The charger can act as a master to initiate charging, which allows the charger to poll batteries for charging information. The PIC16C73A then makes autonomous battery selection decisions.

Schematic

PICREF-5 Features:

• Autonomous charging
- Auto detect AC and battery
- Immediate power source selection
• Charges battery packs of up to 18V at 3.8A
• 3-diode mode for continuous power output
• Chemistry independence
• “Wake-up” charge
• Thermistor safety monitoring

PCB Layout

List of materials

Source: http://www.microchip.com/