DRIVER

DRIVER

LEVEL

SHIFT

UVLO

UVLO

HI

VDD

L

I

VSS

HB

HO

HS

LO

HV

VDD

Copyright © 2016, Texas Instruments Incorporated

8

LM5109A

SNVS412C – APRIL 2006 – REVISED SEPTEMBER 2016

www.ti.com

Product Folder Links: LM5109A

Submit Documentation Feedback

Copyright © 2006–2016, Texas Instruments Incorporated

7 Detailed Description

7.1 Overview

The LM5109A is a cost-effective, high-voltage gate driver designed to drive both the high-side and the low-side

N-channel FETs in a synchronous buck or a half-bridge configuration. The outputs are independently controlled

with TTL compatible input thresholds. The floating high-side driver is capable of working with HB voltage up to

108 V. An external high-voltage diode must be provided to charge high-side gate drive bootstrap capacitor. A

robust level shifter operates at high speed while consuming low power and providing clean level transitions from

the control logic to the high-side gate driver. Undervoltage lockout (UVLO) is provided on both the low-side and

the high-side power rails.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Start-Up and UVLO

Both top and bottom drivers include UVLO protection circuitry which monitors the supply voltage (VDD) and

bootstrap capacitor voltage (VHB–HS) independently. The UVLO circuit inhibits the output until sufficient supply

voltage is available to turn on the external MOSFETs, and the built-in UVLO hysteresis prevents chattering

during supply voltage variations. When the supply voltage is applied to the VDD pin of the LM5109A, the top and

bottom gates are held low until VDD exceeds the UVLO threshold, typically about 6.7 V. Any UVLO condition on

the bootstrap capacitor (VHB–HS) will only disable the high-side output (HO).

7.3.2 Level Shift

The level shift circuit is the interface from the high-side input to the high-side driver stage which is referenced to

the switch node (HS). The level shift allows control of the HO output which is referenced to the HS pin and

provides excellent delay matching with the low-side driver.