ST L6743D 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

■ SO8 package

Applications

■ High current VRM / VRD for desktop / server /

workstation CPUs

■ High current and high efficiency DC / DC

converter

L6743D

High current MOSFET driver

SO8

Combined with ST PWM controllers, the driver allows implementing complete voltage regulator solutions for modern high-current CPUs and DCDC conversion in general. L6743D embeds high-current drivers for both high-side and lowside MOSFETS. The device accepts flexible power supply (5 V to 12 V) to optimize the gatedrive voltage for high-side and low-side maximizing the system efficiency.

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.

L6743D embeds preliminary OV protection: after

Description

L6743D is a flexible, high-frequency dual-driver specifically designed to drive N-channel MOSFETs connected in synchronous-rectified buck topology.

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 SO8 package.

Table 1. Device summary

Order codes Package Packing

L6743D

SO8

L6743DTR Tape and reel

December 2008 Rev 1 1/16

Tube

www.st.com

Contents L6743D

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

2.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3 Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.1 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.2 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4 Device description and operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4.1 High-impedance (HiZ) management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.2 Preliminary OV protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.3 Internal BOOT diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.4 Power dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4.5 Layout guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

5 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

6 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2/16

L6743D 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

PWM Input

DEC

PWM

VCC

BOOT

UGATE

VIN = 5V to 12V

BULK

EN Input

L6743D Reference Schematic

GND

1.2 Block diagram

Figure 2. Block diagram

VCC

15k

GND

PWM

PHASE

L6743D

LGATE

NC*NC*

CONTROL LOGIC

& PROTECTIONS

L6743D

PWM

CROSS CONDUCTION

ADAPTIVE ANTI

VCC

Vout

OUT

BOOT

UGATE

PHASE

LGATE

GND

3/16

Pins description and connection diagrams L6743D

2 Pins description and connection diagrams

Figure 3. Pins connection (Top view)

2.1 Pin description

Table 2. Pins descriptions

Pin # Name Function

high-side driver supply. This pin supplies the high-side floating driver.

1BOOT

2PWM

3EN

Connect through a R Internally connected to the cathode of the integrated bootstrap diode. See

Section 4.3 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 4.1 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 4.1 for details about HiZ.

BOOT

PWM

VCC

L6743D

BOOT

- C

UGATE

PHASE

GND

LGATE

capacitor to the PHASE pin.

BOOT

4VCC

5LGATE

6GND

7 PHASE

8UGATE

4/16

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. Connect directly to the low-side MOSFET gate. A small series resistor can be

useful to reduce dissipated power especially in high frequency applications.

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. This pin is also monitored for the adaptive dead-time management and Pre-OV

Protection.

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

L6743D Pins description and connection diagrams

2.2 Thermal data

Table 3. Thermal data

Symbol Parameter Value Unit

THJA

MAX

STG

TOT

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

85 °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)

1.15 W

5/16

+ 11 hidden pages