SMBus-Controlled Level 2 Multi-Chemistry Battery Charger With Input Current Detect Comparator# BQ24745 Battery Charger Management IC Technical Documentation
Manufacturer : Texas Instruments (TI)
## 1. Application Scenarios
### Typical Use Cases
The BQ24745 is a synchronous battery charger controller IC designed for 2-4 series Li-ion/Li-polymer battery packs in various portable electronic systems. Primary applications include:
- Ultrabooks and Notebook Computers : Provides efficient battery charging while supporting system power demands
- Portable Medical Equipment : Enables reliable battery management for handheld diagnostic devices and monitoring equipment
- Industrial Handheld Terminals : Supports extended battery life in ruggedized mobile computing devices
- Professional Audio/Video Equipment : Manages power delivery for portable recording and broadcasting gear
- IoT Gateways and Edge Devices : Facilitates intelligent charging for always-connected embedded systems
### Industry Applications
- Consumer Electronics : High-performance laptops, gaming devices, and premium tablets
- Healthcare : Portable patient monitors, diagnostic scanners, and medical carts
- Industrial Automation : Handheld test equipment, data collection devices, and mobile scanners
- Telecommunications : Field testing equipment and portable communication devices
- Professional AV : Portable mixing consoles, field recorders, and broadcast equipment
### Practical Advantages and Limitations
Advantages:
- High Efficiency : Synchronous buck topology achieves up to 97% efficiency, reducing thermal stress
- Flexible Input Sources : Supports 5-24V adapter input range with automatic source detection
- Advanced Charging Algorithms : Implements constant current/constant voltage (CC/CV) profiling with temperature monitoring
- System Power Management : Integrates power path management for simultaneous system operation and battery charging
- Compact Solution : Requires minimal external components, reducing PCB footprint
Limitations:
- Battery Chemistry Specific : Optimized for Li-ion/Li-polymer only, not suitable for lead-acid or NiMH batteries
- External MOSFET Requirement : Requires external power MOSFETs and current sensing resistor
- Complex Configuration : Multiple configuration pins and registers may require careful setup
- Thermal Management : High-current applications necessitate proper thermal design considerations
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Inadequate Input Capacitor Selection
- Issue : Insufficient input capacitance causing voltage droop during load transients
- Solution : Use low-ESR ceramic capacitors (22-47μF) close to VIN pin, with bulk capacitance (100-220μF) for high-current applications
Pitfall 2: Poor Current Sensing Accuracy
- Issue : Incorrect RSENSE resistor selection or poor layout affecting charge current regulation
- Solution : Use 1% tolerance current sense resistor, place close to IC, and use Kelvin connections
Pitfall 3: Inefficient Thermal Management
- Issue : Overheating during high-current charging operations
- Solution : Implement proper PCB copper pours for MOSFETs, consider thermal vias, and ensure adequate airflow
Pitfall 4: Incorrect Battery Detection
- Issue : Failure to properly detect battery presence/absence
- Solution : Configure BATDEP pin correctly and implement proper battery detection circuitry
### Compatibility Issues with Other Components
Power Management ICs:
- Ensure compatibility with system PMICs regarding voltage sequencing
- Coordinate with fuel gauge ICs (such as TI's Impedance Track™ devices) for accurate battery monitoring
Microcontroller Interfaces:
- I²C interface operates at 3.3V logic levels - requires level shifting if MCU uses different voltage
- Ensure SMBus timing compatibility with host controller
External MOSFET Selection:
- Must select MOSFETs with appropriate VDS rating (>30V recommended)
- Gate charge characteristics must match driver capability
- Pay attention to RDS(ON)
