Max

HB

To

SW

tal

G

S

W

B

S

H

D

I

0.95

0.2 mA

Q

Q

I

17 nC 10 A

17.5 nC

500 kHz

500 kH

¦

¦

z

u

P u

HB

DD

DH

HBL

V

V

V

V

10 V

1 V

6.7 V

2.3 V

'

LM5109

PWM

Controller

VIN

T1

RGATE

CBOOT

0.1 µF

1.0 µF

VDD

VCC

OUT1

OUT2

VDD

HI

LI

VSS

HS

LO

HO

HB

RBOOT

RGATE

DBOOT

Secondary

Side Circuit

Anti-parallel Diode

(Optional)

11

LM5109A

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SNVS412C – APRIL 2006 – REVISED SEPTEMBER 2016

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8.2 Typical Application

Figure 14. LM5109A Driving MOSFETs in a Half-Bridge Converter

8.2.1 Design Requirements

Table 2 lists the design parameters of the LM5109A.

Table 2. Design Example

PARAMETER

VALUE

Gate Driver

LM5109A

MOSFET

CSD19534KCS

VDD

10 V

QG

17 nC

fSW

500 kHz

8.2.2 Detailed Design Procedure

8.2.2.1 Select Bootstrap and VDD Capacitor

The bootstrap capacitor must maintain the VHB-HS voltage above the UVLO threshold for normal operation.

Calculate the maximum allowable drop across the bootstrap capacitor with Equation 1.

where

•

VDD = Supply voltage of the gate drive IC

•

VDH = Bootstrap diode forward voltage drop

•

VHBL = VHBRmax – VHBH, HB falling threshold

(1)

Then, the total charge needed per switching cycle is estimated by Equation 2.

where

•

QG = Total MOSFET gate charge