6CH Motor Drive IC# Technical Documentation: FAN8702B High-Voltage Half-Bridge Gate Driver IC
Manufacturer: FAT (Fairchild Semiconductor / ON Semiconductor product line)
Document Version: 1.0
Last Updated: October 2023
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## 1. Application Scenarios
### 1.1 Typical Use Cases
The FAN8702B is a monolithic high-voltage, high-speed power MOSFET and IGBT driver designed to operate with supply voltages up to 600V. It features independent high-side and low-side referenced output channels with a typical propagation delay of 50ns. The floating high-side channel can operate with bootstrap or isolated bias supply configurations.
Primary applications include:
- Switch-Mode Power Supplies (SMPS): Particularly in half-bridge, full-bridge, and two-switch forward converter topologies where high-side switching is required.
- Motor Drive Circuits: For driving the high-side and low-side MOSFETs/IGBTs in three-phase inverter bridges for BLDC, PMSM, or AC induction motor control.
- DC-AC Inverters: In UPS systems, solar microinverters, and frequency drives where efficient high-voltage switching is critical.
- Electronic Ballasts & Lighting: For driving power switches in high-intensity discharge (HID) lamp ballasts and high-power LED drivers.
### 1.2 Industry Applications
- Industrial Automation: Motor drives for conveyor systems, robotics, and CNC machinery.
- Consumer Electronics: High-power audio amplifiers, flat-panel TV power supplies.
- Renewable Energy: Inverter stages for solar and wind power conversion systems.
- Automotive: Emerging applications in electric vehicle auxiliary power modules and onboard chargers (requires careful qualification for automotive-grade requirements).
- Telecommunications: High-efficiency rectifiers and DC-DC converters in server power supplies and base station power systems.
### 1.3 Practical Advantages and Limitations
Advantages:
- High Voltage Capability: 600V rail voltage allows direct use in offline applications (85-265VAC) without additional voltage level shifters.
- Fast Switching: Typical propagation delay of 50ns enables high-frequency operation (up to several hundred kHz), reducing magnetic component size.
- Integrated Bootstrap Functionality: Simplifies high-side drive by eliminating the need for isolated power supplies in many applications.
- Robustness: Under-voltage lockout (UVLO) for both channels prevents malfunction during power-up/power-down sequences.
- Compact Solution: Monolithic design reduces component count compared to discrete driver solutions.
Limitations:
- Bootstrap Limitation: In continuous 100% duty cycle applications, the bootstrap capacitor may discharge, requiring an isolated bias supply.
- dv/dt Immunity: While rated for high voltage, extremely fast voltage transients (exceeding 50V/ns) may cause parasitic turn-on; careful layout is essential.
- Peak Current: The 2.5A source/3.5A sink capability may be insufficient for very large MOSFETs/IGBTs without additional buffer stages.
- Temperature Constraints: Junction temperature range of -40°C to +150°C may require thermal management in high-ambient environments.
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## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
Pitfall 1: Bootstrap Capacitor Discharge in High-Duty-Cycle Applications
- Problem: When the high-side switch remains on for extended periods (>95% duty cycle), the bootstrap capacitor discharges below UVLO threshold.
- Solution: Implement an isolated bias supply (transformer-coupled or isolated DC-DC) for the high-side channel or add a charge pump circuit.
Pitfall 2: Shoot-Through Current During Switching Transitions
- Problem: Simultaneous conduction of high-side and low-side switches
