LM5113

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SNVS725E – JUNE 2011 – REVISED JANUARY 2012

Figure 16. LO&HO Gate Drive — High/Low Level Output Voltage

vs Temperature

Figure 17. HB Regulation Voltage

vs

Temperature

Unless otherwise specified, VDD = VHB = 5V, VSS = VHS = 0V.

Detailed Operating Description

The LM5113 is designed to drive both the high-side and the low-side enhancement mode Gallium Nitride FETs in

a synchronous buck or a half-bridge configuration. The outputs of the LM5113 are independently controlled with

TTL input thresholds. The inputs of the LM5113 can withstand voltages up to 14V regardless of the VDD voltage,

and can be directly connected to the outputs of PWM controllers.

The high side driver uses the floating bootstrap capacitor voltage to drive the high-side FET. As shown in

Figure 1, the bootstrap capacitor is recharged through an internal bootstrap diode each cycle when the HS pin is

pulled below the VDD voltage. For inductive load applications the HS node will fall to a negative potential,

clamped by the low side FET.

Due to the intrinsic feature of enhancement mode GaN FETs the source-to-drain voltage, when the gate is pulled

low, is usually higher than a diode forward voltage drop. This can lead to an excessive bootstrap voltage that can

damage the high-side GaN FET. The LM5113 solves this problem with an internal clamping circuit that prevents

the bootstrap voltage from exceeding 5.2V typical.

The output pull-down and pull-up resistance of LM5113 is optimized for enhancement mode GaN FETs to

achieve high frequency, efficient operation. The 0.6

Ω pull-down resistance provides a robust low impedance turn-

off path necessary to eliminate undesired turn-on induced by high dv/dt or high di/dt. The 2.1

Ω pull-up resistance

helps reduce the ringing and over-shoot of the switch node voltage. The split outputs of the LM5113 offer

flexibility to adjust the turn-on and turn-off speed by independently adding additional impedance in either the turn-

on path and/or the turn-off path.

Copyright © 2011–2012, Texas Instruments Incorporated

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