ST L6747A 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 overvoltage (OV) protection

■ VFDFPN8 3x3 mm package

Applications

■ High current VRM / VRD for desktop / server /

workstation CPUs

■ High current and high efficiency DC-DC

converters

Description

The L6747A is a flexible, high-frequency dualdriver specifically designed to drive N-channel MOSFETs connected in synchronous-rectified buck topology.

L6747A

High current MOSFET driver

VFDFPN8 3x3 mm

regulator solutions for modern high-current CPUs and for DC-DC conversion in general.

The L6747A embeds high-current drivers for both high-side and low-side MOSFETS. The device accepts a flexible power supply of 5 V to 12 V. This allows optimization of the high-side and lowside gate-drive voltage to maximize system efficiency.

The embedded bootstrap diode eliminates the need for external diodes. Anti shoot-through management prevents the high-side and low-side MOSFETs from conducting simultaneously and, combined with adaptive dead-time control, minimizes the LS body diode conduction time.

The L6747A features preliminary OV protection to protect the load from dangerous overvoltage due to MOSFET failures at startup.

The L6747A device is available in a VFDFPN8 3x3 mm package.

Combined with ST PWM controllers, the driver allows the implementation of complete voltage

Table 1. Device summary

Order code Package Packing

L6747A VFDFPN8 Tube

L6747ATR VFDFPN8 Tape and reel

March 2010 Doc ID 17126 Rev 1 1/15

www.st.com

Contents L6747A

Contents

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

2 Pin information and thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.1 Pin information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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 BOOT capacitance design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

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

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

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

6 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2/15 Doc ID 17126 Rev 1

L6747A Typical application circuit and block diagram

1 Typical application circuit and block diagram

Figure 1. L6747A typical application circuit

VCC = 5V to 12V

CDEC

VCC

BOOT

PWM Input

EN Input

L6747A Reference Schematic

PWM

GND

UGATE

PHASE

L6747A

LGATE

Figure 2. L6747A block diagram

VCC

70k

L6747A

CROSS CONDUCTION

ADAPTIVE ANTI

VCC

VIN = 5V to 12V

CBULK

Vout

COUT

BOOT

UGATE

10k10k

PHASE

PWM

CONTROL LOGIC

& PROTECTIONS

Doc ID 17126 Rev 1 3/15

PWM

LGATE

GND

Pin information and thermal data L6747A

2 Pin information and thermal data

2.1 Pin information

Figure 3. Pin connection diagram (top view)

BOOT

PWM

VCC

Table 2. Pin descriptions

Pin # Name Function

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

1BOOT

2PWM

3EN

(2.2Ω - 220nF typ.) network to the PHASE pin.

BOOT

Internally connected to the cathode of the integrated bootstrap diode. See Section 4.3 for guidance in selecting the capacitor value.

Control input for the driver; 5V compatible, internally clamp to 3.3V. This pin controls the state of the driver and which external MOSFET must be

turned ON according to EN status. It manages the high-impedance (HiZ) state which sets all the MOSFETs to OFF if externally set in the HiZ window (see Tab l e 5). See Section 4.1 for details of HiZ.

Enable input for the driver; 5V compatible, internally clamp to 3.3V. Pull high to enable the driver based on the PWM status.

Pull low to enter HiZ state with all MOSFETs OFF, regardless of the PWM status. See Section 4.1 for details of HiZ.

L6747A

UGATE PHASE GND LGATE

BOOT

Device and LS driver power supply.

4VCC

5LGATE

6GND

7 PHASE

4/15 Doc ID 17126 Rev 1

Connect to any voltage between 5V and 12V. Bypass with low-ESR MLCC capacitor to GND (1µF typ).

Low-side driver output. Connect directly to the low-side MOSFET gate. A small series resistor may be

used 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 adaptive dead-time management and pre-OV protection. Internal clamp circuitry prevents leakage from this pin in disable conditions.

L6747A Pin information and thermal data

Table 2. Pin descriptions (continued)

Pin # Name Function

High-side driver output.

8UGATE

Connect to high-side MOSFET gate. A small series resistor may be used to control the PHASE pin negative spike.

-TH. PAD

2.2 Thermal data

Table 3. Thermal data

Symbol Parameter Value Unit

THJA

THJC

MAX

STG

TOT

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

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

45 °C/W

2.25 W

Doc ID 17126 Rev 1 5/15

+ 10 hidden pages