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
1
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
C
PWM Input
DEC
PWM
VCC
BOOT
UGATE
HS
HF
C
VIN = 5V to 12V
C
BULK
EN Input
L6743D Reference Schematic
EN
GND
1.2 Block diagram
Figure 2. Block diagram
VCC
EN
15k
GND
PWM
PHASE
L6743D
LGATE
NC*NC*
CONTROL LOGIC
& PROTECTIONS
L6743D
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 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
EN
VCC
1
2
L6743D
3
4
BOOT
- C
8
UGATE
7
PHASE
6
GND
5
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
R
T
T
P
THJA
MAX
STG
T
J
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
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