Semi, Inc - 1.7A/2.5A PWM Step-Up DC/DC Converters In MSOP # ACT6391 Technical Documentation
## 1. Application Scenarios
### Typical Use Cases
The ACT6391 is a high-efficiency, synchronous step-down DC-DC converter primarily employed in power management applications requiring precise voltage regulation and high power density. Key use cases include:
- Portable Electronics : Smartphones, tablets, and wearable devices benefit from its compact footprint and high efficiency across varying load conditions
- IoT Devices : Battery-powered sensors and edge computing modules utilize its low quiescent current and excellent light-load efficiency
- Industrial Control Systems : PLCs, motor controllers, and automation equipment leverage its robust performance in noisy environments
- Embedded Systems : Single-board computers, FPGA power rails, and processor core voltage supplies
### Industry Applications
- Consumer Electronics : Power management for display panels, camera modules, and audio subsystems
- Telecommunications : Base station equipment, network switches, and router power supplies
- Automotive : Infotainment systems, ADAS modules, and body control modules (industrial temperature grade variants)
- Medical Devices : Portable diagnostic equipment and patient monitoring systems
### Practical Advantages
- High Efficiency : Up to 95% efficiency across wide load ranges (10mA to 3A)
- Compact Solution : Integrated MOSFETs and minimal external components reduce board space
- Excellent Transient Response : Fast load step response (<10μs) maintains stable output during rapid current changes
- Wide Input Range : 4.5V to 18V operation supports multiple battery chemistries and power adapters
### Limitations
- Maximum Current : Limited to 3A continuous output current
- Thermal Constraints : Requires proper thermal management at full load conditions
- EMI Considerations : May require additional filtering in noise-sensitive applications
- Cost : Higher component cost compared to non-synchronous alternatives
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Insufficient Input Decoupling
- Problem : Input voltage ringing and instability during load transients
- Solution : Place 10μF ceramic capacitor within 5mm of VIN pin, plus bulk capacitance (47-100μF) for high-current applications
Pitfall 2: Improper Feedback Network Layout
- Problem : Output voltage accuracy degradation and noise susceptibility
- Solution : Route feedback traces away from switching nodes, use Kelvin connection to output capacitor
Pitfall 3: Inadequate Thermal Management
- Problem : Thermal shutdown during high ambient temperature operation
- Solution : Provide adequate copper pour for heat dissipation, consider thermal vias for multilayer boards
### Compatibility Issues
Input Voltage Compatibility
- Ensure input source can handle inrush current during startup
- Verify input voltage remains within 4.5V-18V range under all operating conditions
Load Compatibility
- Check load characteristics for potential stability issues with highly capacitive loads
- Ensure load current requirements don't exceed 3A continuous rating
Control Signal Compatibility
- EN pin logic levels must match controller output specifications
- Soft-start capacitor selection affects compatibility with power sequencing requirements
### PCB Layout Recommendations
Power Stage Layout
- Keep switching loop (VIN, SW, GND) area minimal to reduce EMI
- Place inductor close to SW pin and output capacitors
- Use wide traces for high-current paths (minimum 20 mil width for 3A)
Signal Routing
- Route feedback network away from noisy components and traces
- Keep compensation components close to IC
- Separate analog and power grounds, connecting at single point
Thermal Management
- Use thermal vias under exposed pad for heat dissipation to inner layers
- Provide adequate copper area for heat spreading (minimum 100mm²)
- Avoid placing heat-sensitive components near the converter
Component Placement Priority
1. Input capacitors (closest
