L6747A STMicroelectronics, L6747A Datasheet - Page 8

• Manufacturer Part Number: L6747A
• Description: High current MOSFET driver
• Manufacturer: STMicroelectronics

Specifications of L6747A

• Flexible Gate-drive: 5 V to 12 V compatible

Device description and operation
4
8/15
Device description and operation
The L6747A provides high-current driving control for both high-side and low-side N-channel
MOSFETs, connected as step-down DC-DC converters and driven by an external PWM
signal. The integrated high-current drivers allow the use of different types of power
MOSFETs (also multiple MOS to reduce the equivalent R
transition. The driver for the high-side MOSFET uses the BOOT pin for supply and the
PHASE pin for return. The driver for the low-side MOSFET uses the VCC pin for supply and
the PGND pin for return.
The driver includes anti-shoot-through and adaptive dead-time control to minimize low-side
body diode conduction time, maintaining good efficiency and eliminating the need for
Schottky diodes. When the high-side MOSFET turns off, the voltage on its source begins to
fall; when the voltage falls below the proper threshold, the low-side MOSFET gate drive
voltage is suddenly applied. When the low-side MOSFET turns off, the voltage at the LGATE
pin is sensed. When it drops below the proper threshold, the high-side MOSFET gate drive
voltage is suddenly applied. If the current flowing in the inductor is negative, the source of
the high-side MOSFET never drops. To allow the low-side MOSFET to turn on even in this
case, a watchdog controller is enabled. If the source of the high-side MOSFET does not
drop, the low-side MOSFET is switched on, allowing the negative current of the inductor to
recirculate. This mechanism allows the system to regulate even if the current is negative.
Before V
side MOSFETS firmly OFF. Then, after the UVLO has been crossed, the EN and PWM
inputs take control over the driver’s operations.
The EN pin enables the driver. If low, it keeps all MOSFETs OFF (HiZ) regardless of the
status of PWM. When EN is high, the PWM input takes control. If externally set within the
HiZ window, the driver enters an HiZ state and both MOSFETS are kept in an OFF state
until PWM exits the HiZ window (see
After the UVLO threshold has been crossed and while in HiZ, the preliminary OV protection
is activated. If the voltage sensed through the PHASE pin goes above about 1.8 V, the low-
side MOSFET is latched ON in order to protect the load from dangerous overvoltage. The
driver status is reset from a PWM transition.
Driver power supply, as well as power conversion input, are flexible: 5 V and 12 V can be
chosen for high-side and low-side MOSFET voltage drive.
Figure 4.
PWM
HS Gate
LS Gate
CC
goes above the UVLO threshold, the L6747A keeps both the high-side and low-
Timing diagram (EN = high)
HiZ Window
Doc ID 17126 Rev 1
Figure
4).
t
hold-off
DS(on)
HiZ Window
), maintaining fast switching
t
hold-off
L6747A
V
V
PWM_IH
PWM_IL