8.1 Overview

Figure 10 shows the LMG5200, half-bridge, GaN power stage with highly integrated high-side and low-side gate drivers, which includes built-in UVLO protection circuitry and an overvoltage clamp circuitry. The clamp circuitry limits the bootstrap refresh operation to ensure that the high-side gate driver overdrive does not exceed 5.4 V. The device integrates two, 15-mΩ GaN FETs in a half-bridge configuration. The device can be used in many isolated and non-isolated topologies allowing very simple integration. The package is designed to minimize the loop inductance while keeping the PCB design simple. The drive strengths for turnon and turnoff are optimized to ensure high voltage slew rates without causing any excessive ringing on the gate or power loop.

8.2 Functional Block Diagram

Figure 10 shows the functional block diagram of the LMG5200 device with integrated high-side and low-side GaN FETs.

Figure 10. Functional Block Diagram

8.3 Feature Description

The LMG5200 device brings ease of designing high power density boards without the need for underfill while maintaining creepage and clearance requirements. The propagation delays between the high-side gate driver and low-side gate driver are matched to allow very tight control of dead time. Controlling the dead time is critical in GaN-based applications to maintain high efficiency. HI and LI can be independently controlled to minimize the third quadrant conduction of the low-side FET for hard switched buck converters. A very small propagation mismatch between the HI and LI to the drivers for both the falling and rising thresholds ensures dead times of < 10 ns. Co-packaging the GaN FET half-bridge with the driver ensures minimized common source inductance. This minimized inductance has a significant performance impact on hard-switched topologies.

The built-in bootstrap circuit with clamp prevents the high-side gate drive from exceeding the GaN FETs maximum gate-to-source voltage (Vgs) without any additional external circuitry. The built-in driver has an undervoltage lockout (UVLO) on the VDD and bootstrap (HB-HS) rails. When the voltage is below the UVLO threshold voltage, the device ignores both the HI and LI signals to prevent the GaN FETs from being partially turned on. Below UVLO, if there is sufficient voltage (V_VCC > 2.5 V), the driver actively pulls the high-side and low-side gate driver output low. The UVLO threshold hysteresis of 200 mV prevents chattering and unwanted turnon due to voltage spikes. Use an external VCC bypass capacitor with a value of 0.1 µF or higher. TI recommends a size of 0402 to minimize trace length to the pin. Place the bypass and bootstrap capacitors as close as possible to the device to minimize parasitic inductance.

8.4 Device Functional Modes

The LMG5200 operates in normal mode and UVLO mode. See Start-up and UVLO for information on UVLO operation mode. In the normal mode, the output state is dependent on the states of the HI and LI pins. Table 3 lists the output states for different input pin combinations. Note that when both HI and LI are asserted, both GaN FETs in the power stage are turned on. Careful consideration must be applied to the control inputs in order to avoid this state, as it will result in a shoot-through condition, which can permanently damage the device.