ST L6743B User Manual

Features

■ Dual MOSFET driver for synchronous rectified

converters

■ High driving current for fast external MOSFET

switching

■ Integrated bootstrap diode

■ High frequency operation

■ Enable pin

■ Adaptive dead-time management

■ Flexible gate-drive: 5 V to 12 V compatible

■ High-impedance (HiZ) management for output

stage shutdown

■ Preliminary OV protection

■ VFDFPN8 3 x 3 mm package

L6743B

High current MOSFET driver

VFDFPN8 3 x 3 mm

Combined with ST PWM controllers, the driver
allows implementing complete voltage regulator
solutions for modern high-current CPUs and
DC-DC conversion in general. L6743B embeds
high-current drivers for both high-side and
low-side MOSFETs. The device accepts flexible
power supply (5 V to 12 V) to optimize the
gate-drive voltage for high-side and low-side
maximizing the system efficiency.

Applications

■ High current VRM / VRD for desktop / server /

workstation CPUs

■ High current and high efficiency DC / DC

converters

Description

L6743B is a flexible, high-frequency dual-driver
specifically designed to drive N-channel
MOSFETs connected in synchronous-rectified
buck topology.

Table 1. Device summary

Order code Package Packing

L6743B

VFDFPN8

L6743BTR Tape and reel

The bootstrap diode is embedded saving the use
of external diodes. Anti shoot-through
management avoids high-side and low-side
MOSFET to conduct simultaneously and,
combined with adaptive dead-time control,
minimizes the LS body diode conduction time.

L6743B embeds preliminary OV protection: after
Vcc overcomes the UVLO and while the device is
in HiZ, the LS MOSFET is turned ON to protect
the load in case the output voltage overcomes a
warning threshold protecting the output against
HS failures.

The driver is available is VFDFPN8 3 x 3 mm
packages.

Tube

June 2008 Rev 1 1/16

www.st.com

1

Contents L6743B

Contents

1 Typical application circuit and block diagram . . . . . . . . . . . . . . . . . . . . 3

1.1 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Pins description and connection diagrams . . . . . . . . . . . . . . . . . . . . . . 4

2.1 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.1 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4 Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4.1 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

5 Device description and operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5.1 High-impedance (HiZ) management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

5.2 Preliminary OV protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

5.3 Internal BOOT diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5.4 Power dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5.5 Layout guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

7 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

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L6743B Typical application circuit and block diagram

1 Typical application circuit and block diagram

1.1 Application circuit

Figure 1. Typical application circuit

VCC = 5V to 12V

C

PWM Input

DEC

PWM

VCC

BOOT

UGATE

HS

HF

C

VIN = 5V to 12V

C

BULK

EN Input

L6743B Reference Schematic

EN

GND

1.2 Block diagram

Figure 2. Block diagram

VCC

EN

15k

GND

PWM

PHASE

L6743B

LGATE

CONTROL LOGIC

& PROTECTIONS

L6743B

PWM

L

LS

CROSS CONDUCTION

ADAPTIVE ANTI

HS

VCC

LS

Vout

C

OUT

BOOT

UGATE

PHASE

LGATE

GND

3/16

Pins description and connection diagrams L6743B

2 Pins description and connection diagrams

Figure 3. Pins connection (top view)

2.1 Pin description

Table 1. Pin description

Pin # Name Function

High-side driver supply.
This pin supplies the high-side floating driver. Connect through a

1BOOT

2PWM

3EN

R

BOOT

- C

capacitor to the PHASE pin.

BOOT

Internally connected to the cathode of the integrated bootstrap diode. See

Section 5.3 for guidance in designing the capacitor value.

Control input for the driver, 5 V compatible.
This pin controls the state of the driver and which external MOSFET have to

be turned-ON according to EN status. If left floating and in conjunction with EN
asserted, it causes the driver to enter the high-impedance (HiZ) state which
causes all MOSFETs to be OFF. See Section 5.1 for details about HiZ.

Enable input for the driver. Internally pulled low by 15 kΩ.
Pull high to enable the driver according to the PWM status. If pulled low will

cause the drive to enter HiZ state with all MOSFET OFF regardless of the
PWM status.

See Section 5.1 for details about HiZ.

4VCC

Device and LS driver power supply. Connect to any voltage between 5 V and
12 V. Bypass with low-ESR MLCC capacitor to GND.

Low-side driver output.

5LGATE

Connect directly to the low-side MOSFET gate. A small series resistor can be
useful to reduce dissipated power especially in high frequency applications.

6GND

All internal references, logic and drivers are referenced to this pin. Connect to
the PCB ground plane.

high-side driver return path. Connect to the high-side MOSFET source.

7 PHASE

This pin is also monitored for the adaptive dead-time management and pre­OV protection.

8UGATE

-TH. PAD

high-side driver output.
Connect to high-side MOSFET gate.

Thermal pad connects the silicon substrate and makes good thermal contact
with the PCB. Connect to the PGND plane.

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L6743B Maximum ratings

3 Maximum ratings

3.1 Absolute maximum ratings

Table 2. Absolute maximum ratings

Symbol Parameter Value Unit

V

CC,VPVCC

V

BOOT

V

V

V

PWM, VEN

V

CC,VPVCC

, V

UGATE

PHASE

LGATE

to GND -0.3 to 15 V

to GND
to PHASE

to GND -8 to 26 V

to GND -0.3 to VCC + 0.3 V

to GND -0.3 to 7 V

to GND -0.3 to 15 V

3.2 Thermal data

Table 3. Thermal data

Symbol Parameter Value Unit

R

R

T

T

P

THJA

THJC

MAX

STG

T

J

TOT

Thermal resistance junction to ambient
(Device soldered on 2s2p, 67 mm x 69 mm board)

Thermal resistance junction to case 5 °C/W

Maximum junction temperature 150 °C

Storage temperature range 0 to 150 °C

Junction temperature range 0 to 125 °C

Maximum power dissipation at 25 °C
(Device soldered on 2s2p PC board)

41
15

45 °C/W

2.25 W

V

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