CMOS Monolithic Voltage Converter# Technical Documentation: FAN5660IM High-Efficiency Step-Up DC-DC Converter
Manufacturer: FAIRCHILD (now part of ON Semiconductor)
Component: FAN5660IM
Type: Monolithic, High-Efficiency, Step-Up (Boost) DC-DC Converter
Package: 8-Pin SOIC (IM)
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## 1. Application Scenarios
### Typical Use Cases
The FAN5660IM is a current-mode, fixed-frequency boost converter designed to generate a regulated output voltage higher than its input supply. Its primary use cases include:
* Single-Cell to Multi-Cell Conversion: Efficiently boosting a single Lithium-Ion (2.7V to 4.2V) or 3-cell NiMH/NiCd (~3.6V) battery voltage to standard logic supply rails such as 5V, 3.3V, or adjustable outputs up to 5.5V.
* White LED Backlighting: A classic application is driving series-connected white LEDs for backlighting in portable devices like mobile phones, PDAs, and handheld instruments. The constant-current control capability (when used with external sensing) ensures uniform LED brightness.
* Auxiliary Voltage Rails: Providing a secondary, higher-voltage power rail from a primary system battery or USB port (5V) in compact embedded systems, portable medical devices, and digital cameras.
### Industry Applications
1. Consumer Portable Electronics: Mobile phones, digital still cameras, MP3 players, and GPS units for powering display backlights, audio amplifiers, or peripheral circuits.
2. Handheld Industrial/Medical Devices: Data loggers, portable meters, and diagnostic tools where efficient battery utilization is critical for extended operation.
3. Low-Power Wireless Devices: IoT sensor nodes and Bluetooth modules that require a stable voltage from a decaying battery source.
### Practical Advantages and Limitations
Advantages:
* High Efficiency (Up to 90%): Achieved through a low 0.15Ω internal N-channel MOSFET switch, minimizing conduction losses.
* Low Start-up Voltage: Can begin operation from an input as low as 1.0V, enabling use from nearly depleted batteries.
* Fixed Frequency Operation (1.2MHz): Switches at a high, predictable frequency, which simplifies EMI filtering and allows the use of small, low-profile external inductors and capacitors.
* Integrated Power Switch: Simplifies design and reduces component count compared to controller-only solutions.
* Low Shutdown Current (<1µA): Maximizes battery shelf life when the device is powered off.
Limitations:
* Peak Output Current Constraint: As a monolithic boost converter, the switch current limit (typically ~1.5A) defines the maximum achievable output power. It is not suitable for high-current (>~500mA) applications without careful design.
* Input Voltage Range: The absolute maximum input voltage is 6V, making it unsuitable for systems with input rails like 9V or 12V without pre-regulation.
* Thermal Management in SOIC-8: For continuous high-load operation near its limits, the small package has limited thermal dissipation capability, which may necessitate PCB thermal design or derating.
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## 2. Design Considerations
### Common Design Pitfalls and Solutions
1. Pitfall: Inductor Saturation.
* Cause: Selecting an inductor with a saturation current rating lower than the chip's peak switch current limit.
* Solution: Choose an inductor with a saturation current rating at least 20-30% higher than the calculated peak inductor current. Use the formula: \( I_{L(peak)} = I_{OUT} \times \frac{V_{OUT}}{V_{IN
