High-Performance Half-Bridge Driver: Infineon AUIRS21811STR Datasheet and Application Guide

In the realm of power electronics, the efficiency and reliability of motor drives, switch-mode power supplies (SMPS), and DC-AC inverters heavily depend on the performance of the gate driver IC. The Infineon AUIRS21811STR stands out as a high-voltage, high-speed power MOSFET and IGBT driver specifically designed to control both high-side and low-side switches in a half-bridge configuration. This article delves into the key specifications from its datasheet and provides essential guidance for its application.

Core Features and Electrical Characteristics

Housed in a compact SO-8 package, the AUIRS21811STR is engineered for robustness and performance. Its operational principle is centered on a floating channel design for the high-side driver, which allows it to drive an N-channel MOSFET or IGBT that is connected to a bus voltage far exceeding the IC's supply voltage (VCC). This is achieved through a bootstrap circuitry method, a critical feature detailed in the application notes.

The driver accepts logic-level inputs (from 3.3 V to 20 V) and is compatible with a wide range of microcontrollers and DSPs. It delivers typical peak output currents of 1.4 A (source) and 1.8 A (sink), enabling rapid switching of power devices. This strong drive capability is paramount for minimizing switching losses, a key factor in achieving high system efficiency, especially at high frequencies.

A vital specification for system safety is the built-in dead time. The AUIRS21811STR features an internal dead time of 310 ns (typical), which prevents shoot-through currents by ensuring that the high-side and low-side switches are never conducting simultaneously. This protects the power devices from catastrophic failure. Furthermore, the IC boasts a high level of integration, including protection features such as undervoltage lockout (UVLO) for both the high-side and low-side sections. UVLO ensures the power switches are only driven when the gate voltage is sufficient for a defined RDS(on), preventing operation in a high-resistance linear mode that could lead to thermal overload.

Application Guide and Circuit Design Considerations

Successful implementation of the AUIRS21811STR requires careful attention to the board layout and external component selection.

1. Bootstrap Circuit: The heart of the high-side drive is the bootstrap component network. A fast-recovery or Schottky bootstrap diode (D_BS) is mandatory to efficiently charge the bootstrap capacitor (C_BS) during the low-side switch's on-time. The value of C_BS must be carefully calculated to hold sufficient charge to keep the high-side driver operational during the maximum duty cycle without a significant voltage drop. The datasheet provides formulas and recommendations for selecting these components based on the gate charge (Qg) of the power MOSFET and the operating frequency.

2. Gate Resistors (R_G): The selection of gate resistors is a critical trade-off. A lower value resistor allows for faster switching, reducing switching losses but potentially increasing electromagnetic interference (EMI) and voltage overshoot due to parasitic inductance. A higher value dampens these effects but increases switching losses. Optimizing the R_G value is essential for balancing efficiency and EMI performance.

3. PCB Layout: A proper PCB layout is non-negotiable for high-speed switching circuits. Key guidelines include:

Minimizing loop areas, especially for the high-current paths (bootstrap capacitor, gate drive loops, and the power stage).

Using a low-inductance ground plane.

Placing the decoupling capacitor for VCC (typically a 100 nF ceramic capacitor in parallel with a larger electrolytic capacitor) as close as possible to the VCC and COM pins.

Keeping the gate drive traces short and direct to minimize parasitic inductance.

ICGOODFIND: The Infineon AUIRS21811STR is a highly integrated and robust solution for half-bridge applications, offering strong drive strength, essential protective features, and design flexibility. Its performance makes it an excellent choice for demanding applications in industrial motor control, appliance drives, and power conversion systems. Proper attention to the bootstrap design, component selection, and PCB layout is crucial to unlocking its full potential.

Keywords: Half-Bridge Driver, Bootstrap Circuit, Undervoltage Lockout (UVLO), Gate Driver IC, Dead Time.