The LMG2650 is a highly-integrated 650V 95mΩ GaN power-FET half bridge intended for use in switch-mode power-supply applications. The LMG2650 combines the half-bridge power FETs, gate drivers, low-side current-sense emulation function, high-side gate-drive level shifter, and bootstrap diode function in a 6mm by 8mm QFN package.

The 650V rated GaN FETs support the high voltages encountered in off-line power switching applications. The GaN FETs low output-capacitive charge reduces both the time and energy needed for power converter switching and is the key characteristic needed to create small, efficient power converters.

The LMG2650 internal gate drivers regulate the GaN FET gate voltage for optimum on-resistance. Internal drivers also reduce total gate inductance and GaN FET common-source inductance for improved switching performance. The low-side / high-side GaN FET turn-on slew rates can be individually programmed to one of four discrete settings for design flexibility with respect to power loss, switching-induced ringing, and EMI.

Current-sense emulation places a scaled replica of the low-side drain current on the output of the CS pin. The CS pin is terminated with a resistor to AGND to create the current-sense input signal to the external power supply controller. This CS pin resistor replaces the traditional current-sense resistor, placed in series with the low-side GaN FET source, at significant power and space savings. Furthermore, with no current-sense resistor in series with the GaN source, the low-side GaN FET thermal pad (SL pin) can be connected directly to the PCB power ground, improving system thermal performance.

The high-side GaN FET is controlled by both the low-side referenced INH pin and high-side referenced GDH pin allowing the LMG2650 to interface with controllers that employ either high-side gate drive reference scheme. The internal high-side gate-drive level-shifter reliably transmits the INH signal to the high-side with minimal impact to device quiescent current and no impact to device start-up time.

The bootstrap diode function between AUX and BST is implemented with a smart-switched GaN bootstrap FET. The switched GaN bootstrap FET allows more complete charging of the BST-to-SW capacitor since the on-state GaN bootstrap FET does not have the forward voltage drop of a traditional bootstrap diode. The smart-switched GaN bootstrap FET also avoids the traditional bootstrap diode problem of BST-to-SW capacitor overcharging due to off-state third-quadrant current flow in the low-side half-bridge GaN power FET. Finally, the bootstrap function has more efficient switching due to low capacitance and no reverse-recovery charge compared to the traditional bootstrap diode.

The AUX input supply wide voltage range is compatible with the corresponding wide range supply rail created by power supply controllers. The BST input supply range is even wider on the low end to account for capacitive droop in between bootstrap recharge cycles. Low AUX/BST idle quiescent currents and fast BST start-up time support converter burst-mode operation critical for meeting government light-load efficiency mandates. Further AUX quiescent current reduction is obtained by placing the device in standby mode with the EN pin.

The EN, INL, INH, and GDH control pins have high input impedance, low input threshold voltage and maximum input voltage equal to the local supply pin voltage (AUX or BST to SW). This allows the pins to support both low voltage and high voltage input signals and be driven with low-power outputs.

The LMG2650 protection features are low-side / high-side under-voltage lockout (UVLO), INL/INH input gate-drive interlock, low-side/high-side cycle-by-cycle current limit, and low-side/high-side overtemperature shut down. The UVLO features also help achieve well-behaved converter operation. The low-side overtemperature shut down is reported on the open drain FLT output.