Multi-Cell Synchronous Switch-mode Charger with System Power Selector 28-VQFN -40 to 125# BQ24750 Battery Charger IC Technical Documentation
Manufacturer : Texas Instruments (TI)
## 1. Application Scenarios
### Typical Use Cases
The BQ24750 is a synchronous battery charger IC designed primarily for 2-4 series Li-ion/Li-polymer battery packs in space-constrained portable devices. Key applications include:
- Ultrabook and Notebook Computers : Provides efficient charging for 2-4 cell battery configurations (7.4V-16.8V) with up to 10A charge current capability
- Portable Medical Devices : Enables reliable battery management in handheld diagnostic equipment and portable monitoring systems
- Industrial Tablets and Handheld Terminals : Supports ruggedized portable computing devices requiring robust power management
- High-Performance Mobile Workstations : Manages power delivery for demanding portable computing applications
### Industry Applications
- Consumer Electronics : Premium laptops, convertible tablets, and high-end portable gaming systems
- Healthcare : Portable ultrasound devices, patient monitors, and mobile diagnostic equipment
- Industrial Automation : Handheld scanners, portable data collection terminals, and field service devices
- Telecommunications : Portable network testing equipment and field communication devices
### Practical Advantages and Limitations
Advantages:
- High Efficiency : Synchronous buck architecture achieves up to 97% efficiency, reducing thermal dissipation
- Flexible Input Sources : Supports adapter inputs from 5V to 24V with automatic source detection
- Advanced Power Path Management : Enables system operation while charging and instant-on capability
- Integrated Protection : Comprehensive safety features including over-voltage, over-current, and thermal shutdown
- I²C Programmable : Allows dynamic adjustment of charge parameters for optimal performance
Limitations:
- Battery Chemistry Restriction : Limited to Li-ion/Li-polymer chemistries only
- Maximum Input Voltage : 24V maximum limits compatibility with some industrial power supplies
- Thermal Constraints : High current charging (>6A) may require significant thermal management
- Complex Implementation : Requires careful PCB layout and system integration expertise
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Inadequate Thermal Management
- Issue : Excessive junction temperatures during high-current charging
- Solution : Implement proper thermal vias, adequate copper area, and consider external heatsinking for currents above 6A
Pitfall 2: Input Capacitor Selection
- Issue : Insufficient input capacitance causing voltage spikes and system instability
- Solution : Use low-ESR ceramic capacitors close to VIN pin (typically 22μF-47μF)
Pitfall 3: Inductor Saturation
- Issue : Inductor saturation at peak currents leading to efficiency degradation
- Solution : Select inductors with saturation current rating ≥ 1.3× maximum charge current
Pitfall 4: Battery Detection Issues
- Issue : False battery detection or failure to recognize battery presence
- Solution : Proper configuration of BATDEP and ACPRES thresholds via I²C
### Compatibility Issues with Other Components
Microcontroller Interface:
- Ensure I²C pull-up resistors (typically 4.7kΩ) are properly sized for bus speed
- Verify voltage level compatibility between host processor and BQ24750
Power MOSFET Selection:
- Use low RDS(ON) MOSFETs with Qg < 30nC for optimal switching performance
- Ensure gate drivers are compatible with the IC's drive capability
Battery Pack Integration:
- Compatible with standard 2-4S battery protection circuits
- Requires communication with smart battery packs for optimal performance
### PCB Layout Recommendations
Power Stage Layout:
- Place input capacitors (CIN) as close as possible to VIN and PGND
