L6743B STMicroelectronics, L6743B Datasheet - Page 7

• Manufacturer Part Number: L6743B
• Description: MOSFET & Power Driver ICs Hi-current MOSFET Driver
• Manufacturer: STMicroelectronics
• Type: High Current Mosfet Driverr

Specifications of L6743B

• Product: Driver ICs - Various
• Propagation Delay Time: 75 ns
• Supply Voltage (max): 12 V
• Supply Voltage (min): 5 V
• Supply Current: 5 mA
• Maximum Power Dissipation: 2.25 W
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Package / Case: SO-8
• Minimum Operating Temperature: 0 C
• Number Of Drivers: 2
• Number Of Outputs: 2
• Output Voltage: 10 V
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

L6743B
5
Device description and operation
L6743B provides high-current driving control for both high-side and low-side N-channel
MOSFETS connected as step-down DC-DC converter driven by an external PWM signal.
The integrated high-current drivers allow using different types of power MOSFETs (also
multiple MOS to reduce the equivalent R
The driver for the high-side MOSFET use BOOT pin for supply and PHASE pin for return.
The driver for the low-side MOSFET use the VCC pin for supply and PGND pin for return.
The driver embodies a anti-shoot-through and adaptive dead-time control to minimize low-
side body diode conduction time maintaining good efficiency saving the use of Schottky
diodes: when the high-side MOSFET turns off, the voltage on its source begins to fall; when
the voltage reaches about 2 V, the low-side MOSFET gate drive voltage is suddenly applied.
When the low-side MOSFET turns off, the voltage at LGATE pin is sensed. When it drops
below about 1 V, the high-side MOSFET gate drive voltage is suddenly applied. If the
current flowing in the inductor is negative, the source of high-side MOSFET will never drop.
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 doesn't drop, the low-side MOSFET is
switched on so allowing the negative current of the inductor to recirculate. This mechanism
allows the system to regulate even if the current is negative.
Before VCC to overcome the UVLO threshold, L6743B keeps firmly-OFF both high-side and
low-side MOSFETS then, after the UVLO has been crossed, the EN and PWM inputs take
the control over driver’s operations. EN pin enables the driver: if low will keep all MOSFET
OFF (HiZ) regardless of the status of PWM. When EN is high, the PWM input takes the
control: if left floating, the internal resistor divider sets the HiZ State: both MOSFETS are
kept in the OFF state until PWM transition.
After UVLO crossing and while in HiZ, the preliminary-OV protection is activated: if the
voltage senses through the PHASE pin overcomes about 1.8 V, the low-side MOSFET is
latched ON in order to protect the load from dangerous over-voltage. 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
Timing diagram (EN = high)
HiZ Window
DS(on)
, maintaining fast switching transition.
t
hold-off
Device description and operation
HiZ Window
t
hold-off
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