Multi-Cell Synchronous Switch-mode Charger with System Power Selector with Low Iq 28-VQFN -40 to 125# BQ24751ARHDT Technical Documentation
## 1. Application Scenarios
### Typical Use Cases
The BQ24751ARHDT is a high-efficiency, synchronous battery charger controller designed for 2-4 series Li-ion/Li-polymer battery packs. Typical applications include:
- Portable Computing Devices : Notebooks, ultrabooks, and tablet PCs requiring 2-4 cell battery configurations
- Medical Equipment : Portable medical devices requiring reliable battery charging and power path management
- Industrial Handhelds : Ruggedized mobile computers and data collection terminals
- Consumer Electronics : High-end portable audio/video equipment and gaming devices
### Industry Applications
- Mobile Computing : Primary battery charging solution in laptops with smart power management
- Telecommunications : Backup power systems and portable communication equipment
- Automotive Infotainment : In-vehicle entertainment systems with battery backup
- IoT Gateways : Edge computing devices requiring uninterrupted power operation
### Practical Advantages
Strengths:
- High charging efficiency (up to 97%) through synchronous switching architecture
- Advanced power path management enabling system operation from adapter or battery
- Integrated battery authentication support for enhanced safety
- Wide input voltage range (5V to 24V) accommodating various adapter types
- Programmable charge parameters via I²C interface for design flexibility
Limitations:
- Requires external MOSFETs and passive components, increasing board space
- I²C communication dependency for full functionality
- Limited to 4-series battery configurations maximum
- Higher component count compared to integrated charger solutions
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Inadequate Thermal Management
- Issue : External MOSFETs overheating during high-current charging
- Solution : Implement proper heatsinking and use low-RDS(on) MOSFETs with adequate package size
Pitfall 2: Layout-Induced Noise
- Issue : Switching noise affecting sensitive analog circuits
- Solution : Separate power and signal grounds, use star grounding technique
Pitfall 3: Incurrent Limit Setting
- Issue : Adapter overloading during system peak loads
- Solution : Properly configure ACOK and ACOV thresholds based on adapter capability
### Compatibility Issues
Power Source Compatibility:
- Requires compatible adapter detection circuit for optimal operation
- May need level shifting when interfacing with 1.8V I²C hosts
- Ensure battery pack includes proper protection circuitry
System Integration:
- Host processor must support I²C communication at 400kHz
- Compatible with various battery chemistries but requires proper configuration
- Works with both switching and linear power stages
### PCB Layout Recommendations
Power Stage Layout:
- Place input capacitors (C1, C2) as close as possible to VCC and PGND pins
- Keep high-current paths short and wide (minimum 20 mil width for 5A current)
- Use multiple vias for power plane connections to reduce impedance
Signal Integrity:
- Route I²C signals (SDA, SCL) away from switching nodes
- Keep battery sense lines (BATSRN, BATSRP) as a differential pair
- Separate analog and digital grounds, connecting at single point near IC
Thermal Management:
- Provide adequate copper area for MOSFET thermal dissipation
- Use thermal vias under power component packages
- Ensure proper airflow in enclosed systems
## 3. Technical Specifications
### Key Parameter Explanations
Input Specifications:
- Operating Voltage Range : 5V to 24V DC input
- Adapter Current Limit : Programmable from 512mA to 8.192A (10mA steps)
- Input Over-Voltage Protection : 19.2V typical threshold
Charging Parameters
