6-Channel Motor Drive IC# Technical Documentation: FAN8008 - Synchronous Buck Regulator
## 1. Application Scenarios
### 1.1 Typical Use Cases
The FAN8008 from Fairchild (now ON Semiconductor) is a 1.5A synchronous step-down DC-DC converter designed for high-efficiency power conversion in space-constrained applications. Its primary use cases include:
- Point-of-Load (POL) Regulation : Providing stable, clean power rails for sensitive ICs such as FPGAs, DSPs, and ASICs from intermediate bus voltages (e.g., 12V, 5V).
- Battery-Powered Devices : Efficiently stepping down Li-ion/polymer battery voltages (typically 3.7V–4.2V) to lower system voltages (e.g., 1.8V, 1.2V) in portable electronics, extending battery life.
- Distributed Power Architectures : Generating multiple secondary voltages from a single primary supply in systems like networking equipment, industrial controllers, and set-top boxes.
### 1.2 Industry Applications
- Consumer Electronics : Smartphones, tablets, digital cameras, portable media players.
- Telecommunications & Networking : Routers, switches, optical modules, baseband units.
- Industrial Automation : PLCs, sensor modules, motor drive control boards.
- Computing : Motherboard peripheral power, storage devices (SSDs, HDDs), USB-powered peripherals.
### 1.3 Practical Advantages and Limitations
Advantages:
- High Efficiency (Up to 95%) : Achieved through synchronous rectification (using an internal low-Rds(on) MOSFET as the bottom switch) and a low quiescent current (~40µA typical).
- Compact Solution : Available in small packages (e.g., MLP-8L 3x3mm) and requires minimal external components (inductor, input/output capacitors, feedback resistors).
- Wide Input Voltage Range (4.5V to 18V) : Accommodates common unregulated adapters (12V) and battery sources.
- Integrated Features : Includes internal soft-start, cycle-by-cycle current limit, thermal shutdown, and Power Good (PG) output for sequencing/monitoring.
- Fixed-Frequency PWM Operation (1.2MHz) : Enables use of small inductors and capacitors, reduces EMI spectral noise, and eases filter design.
Limitations:
- Maximum Output Current (1.5A) : Not suitable for high-power loads; parallel devices or a higher-current regulator is needed for >1.5A.
- Fixed Switching Frequency : While beneficial for noise predictability, it offers less flexibility in optimizing efficiency vs. size across all load conditions compared to variable-frequency architectures.
- Synchronous Topology : Cannot be used as a boost or inverting regulator; step-down only.
- Minimum Input Voltage (4.5V) : Not suitable for direct operation from single-cell Li-ion (3.0V–4.2V) without a preceding boost stage.
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## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
| Pitfall | Consequence | Solution |
| :--- | :--- | :--- |
| Insufficient Input Capacitance | Input voltage ringing, potential instability, increased EMI. | Place a low-ESR ceramic capacitor (e.g., 10µF X7R) close to the VIN and GND pins. For higher input voltages/long leads, add a bulk capacitor (e.g., 47µF electrolytic). |
| Improper Inductor Selection | Excessive ripple current, reduced efficiency, potential saturation. | Choose an inductor with a saturation current rating >1.5A and low DCR. Ensure its ripple current (ΔIL) is 20
