the FAN7382, a popular half-bridge gate driver IC from onsemi (formerly Fairchild Semiconductor).

Overview

The FAN7382 is a monolithic high-voltage gate drive IC designed to drive both high-side and low-side N-Channel MOSFETs or IGBTs in a half-bridge configuration. It is widely used in switching power applications such as motor drives, power supplies, and inverters for appliances and industrial systems.

Its key function is to translate low-power logic signals from a microcontroller (MCU) or PWM controller into high-current, high-voltage signals necessary to rapidly switch power transistors on and off.

Key Features:

1. High-Voltage Operation: Features a high-side floating channel designed for bootstrap operation, allowing it to drive a high-side switch with a voltage up to +600V.

2. Wide Supply Voltage Range (VCC): The logic and low-side driver operates from 10V to 20V, making it compatible with standard 12V or 15V gate drive supplies.

3. High Output Current: Capable of sourcing/sinking +250 mA / -350 mA peak current. This allows for fast switching of large MOSFET/IGBT gates, minimizing switching losses.

4. Matched Propagation Delays: The propagation delays for the high-side and low-side channels are closely matched (< 50 ns), which is critical for preventing shoot-through currents in the half-bridge.

5. Integrated Dead Time: An internal dead time (typically 540 ns) is generated between the shut-down of one transistor and the turn-on of its complementary partner. This is a crucial safety feature to prevent both transistors in the same leg from being on simultaneously (shoot-through), which would cause a catastrophic short circuit.

6. Under-Voltage Lockout (UVLO): For both the high-side and low-side drivers. If the supply voltage (VCC) drops below a specified threshold (typically ~8.7V), the outputs are disabled, preventing the power switches from operating in a linear (high-loss) region, which could destroy them.

7. dv/dt Immunity: The high-side channel is immune to high voltage transient conditions, ensuring stable operation under noisy switching conditions.

8. CMOS/LSTTL Compatible Inputs: The input pins are compatible with standard 3.3V and 5V logic levels, allowing for direct interfacing with microcontrollers and DSPs.

Pin Configuration (Typically an 8-pin DIP or SOIC)

Internal Block Diagram and How It Works

A simplified explanation of its operation:

1. Input Stage: The logic signals at HIN and LIN are received. The internal logic processes these signals, ensuring they are level-shifted to the correct voltages for the high- and low-side drivers.

2. Dead Time Generation: The internal circuitry automatically inserts a fixed dead time between the falling edge of one signal and the rising edge of the complementary signal.

3. Output Drivers:

   • The Low-Side Driver is referenced to GND. It directly drives the LO pin.

   • The High-Side Driver is a "floating" circuit referenced to the VS pin (the switch node). Its power comes from the voltage between VB and VS. This is generated using a bootstrap circuit.

4. Bootstrap Circuitry (External): This is a critical part of using the FAN7382. It consists of a bootstrap diode (D_BS) and a bootstrap capacitor (C_BS).

   • When the low-side switch (Q2) is ON, the VS pin is pulled close to GND.

   • This allows the VCC supply to charge the capacitor (C_BS) through the diode (D_BS), building up a voltage of ~VCC across it.

   • When the high-side needs to be turned on, the driver uses the charge stored in C_BS to power the high-side gate drive circuit. The voltage at VB becomes VS + V_CBS, providing the necessary voltage to drive the high-side gate above the switch node voltage (VS).