Multi-Cell Synchronous Switch-mode Charger with System Power Selector with Low Iq 28-VQFN -40 to 125# BQ24751ARHDR Technical Documentation
Manufacturer : Texas Instruments (TI)
## 1. Application Scenarios
### Typical Use Cases
The BQ24751ARHDR is a synchronous battery charge controller designed for 2-4 cell Li-ion/Li-polymer battery packs in space-constrained applications. Key use cases include:
- Portable Computing Devices : Notebooks, ultrabooks, and tablets requiring efficient battery charging
- Medical Portable Equipment : Handheld diagnostic devices and portable monitoring systems
- Industrial Handheld Terminals : Ruggedized mobile computers and data collection devices
- Consumer Electronics : High-end cameras, portable audio/video equipment
- IoT Edge Devices : Battery-powered gateways and edge computing systems
### Industry Applications
- Mobile Computing : Provides fast charging for laptops while maintaining thermal safety
- Healthcare : Enables reliable battery management in portable medical equipment
- Industrial Automation : Supports battery-powered handheld instruments and scanners
- Telecommunications : Used in portable communication devices and field equipment
- Consumer Electronics : Powers high-performance portable devices with extended battery life
### Practical Advantages
Strengths:
- High efficiency (up to 97%) with synchronous switching architecture
- Wide input voltage range (5V to 24V) supporting various adapter types
- Integrated MOSFET drivers reducing external component count
- Advanced charge termination with voltage and current regulation
- Comprehensive protection features (OVP, OCP, thermal shutdown)
- I²C interface for programmable charge parameters
Limitations:
- Requires external MOSFETs and sense resistors
- Limited to 2-4 series Li-ion cells (8.4V-16.8V)
- I²C communication necessary for full programmability
- PCB layout sensitivity due to high-frequency switching
- Not suitable for single-cell or 5+ cell battery configurations
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Inadequate Thermal Management
- Issue : Overheating during high-current charging
- Solution : Implement proper heatsinking for external MOSFETs and use thermal vias
Pitfall 2: Input Voltage Transients
- Issue : Adapter plug/unplug events causing voltage spikes
- Solution : Include TVS diodes and adequate input capacitance
Pitfall 3: Battery Detection Failures
- Issue : Incorrect battery presence detection
- Solution : Proper configuration of BATDEP and ACPRES pins with appropriate pull-up/pull-down resistors
Pitfall 4: Charge Current Inaccuracy
- Issue : Deviation from programmed charge current
- Solution : Use high-precision current sense resistors (1% tolerance or better)
### Compatibility Issues
Power Management Integration:
- Compatible with most system power management ICs via I²C
- May require level shifting when interfacing with 1.8V systems
- Ensure compatibility with host processor's I²C implementation
Battery Pack Considerations:
- Requires battery pack with integrated protection circuit
- Compatible with standard 2-4 cell Li-ion/Li-polymer configurations
- Verify battery chemistry compatibility (supports most common Li-ion variants)
Adapter Compatibility:
- Works with various adapter types (19V, 20V typical for notebooks)
- Supports USB-PD sources with appropriate voltage negotiation
### PCB Layout Recommendations
Power Path Layout:
- Keep high-current paths short and wide (minimum 20 mil width for 3A)
- Place input/output capacitors close to IC pins
- Use ground plane for improved thermal performance
Switching Node Considerations:
- Minimize loop area for switching nodes (BOOT, PH, LODRV)
- Keep bootstrap capacitor close to BOOT and PH pins
- Separate analog and power grounds with single-point connection
