L6747A STMicroelectronics, L6747A Datasheet - Page 9

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

Specifications of L6747A

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

L6747A
4.1
4.2
4.3
High-impedance (HiZ) management
The driver is capable of managing a high-impedance conditions by keeping all MOSFETs in
an OFF state. This is achieved in two different ways:
●
●
The device exits from the HiZ state after any PWM transition. See
HiZ timing.
The implementation of the high-impedance state allows the controller connected to the
driver to manage the high-impedance state of its output, preventing the generation of nega-
tive undershoot on the regulated voltage during the shutdown stage. Also, different power
management states may be managed, such as pre-bias startup.
Preliminary OV protection
When V
preliminary OV protection.
The intent of this protection feature is to protect the load during system startup, especially
from high-side MOSFET failures. In fact, VRM, and more generally PWM, controllers, have a
12 V bus-compatible turn-on threshold and are non-operative if V
thresholds (which is in the range of about 10 V). In cases of high-side MOSFET failure, the
controller does not recognize the overvoltage until V
tures are implemented). However, in this case the output voltage is already at the same volt-
age (~10 V) and the load (a CPU in most cases) is already burnt.
The L6747A bypasses the PWM controller by latching on the low-side MOSFET if the
PHASE pin voltage exceeds 1.8 V during the HiZ state. When the PWM input exits from the
HiZ window, the protection is reset and the control of the output voltage is transferred to the
controller connected to the PWM input.
Since the driver has its own UVLO threshold, a simple way to provide protection to the out-
put in all conditions when the device is OFF is to supply the controller through the 5 V
5 V
side MOSFET is driven with 5 V. This ensures reliable protection of the load.
Preliminary OV is active after UVLO and while the driver is in an HiZ state, and it is disabled
after the first PWM transition. The controller must manage its output voltage from that
moment on.
BOOT capacitance design
The L6747A embeds a bootstrap diode to supply the high-side driver, removing the neces-
sity for an external component. Simply connecting an external capacitor between BOOT and
PHASE completes the high-side supply connections.
SB
If the EN signal is pulled low, the device keeps all MOSFETs OFF regardless of the
PWM status.
When EN is asserted, if the PWM signal is externally set within the HiZ window for a
time greater than the hold-off time, the device detects the HiZ condition and turns off all
the MOSFETs. The HiZ window is defined as the PWM voltage range between
V
PWM_HIZ_H
is always present before any other voltage and, in case of high-side short, the low-
CC
exceeds its UVLO threshold while the device is in HiZ, theL6747A activates the
= 1.6 V and V
Doc ID 17126 Rev 1
PWM_HIZ_L
= 1.3 V.
CC
= ~10 V (unless other special fea-
Device description and operation
CC
Figure 4
is below the turn-on
for details about
SB
bus.
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