L6747A STMicroelectronics, L6747A Datasheet - Page 10

• 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
4.4
10/15
The bootstrap capacitor value should be selected to obtain a negligible discharge due to the
turning on of the high-side MOSFET. It must provide a stable voltage supply to the high-side
driver during the MOSFET turn-on, and minimize the power dissipated by the embedded
boot diode.
the bootstrap according to the desired discharge, and the selected MOSFET.
To prevent the bootstrap capacitor from overcharging as a consequence of large negative
spikes, an external series R
series with the BOOT pin.
Figure 5.
Power dissipation
The L6747A embeds high current drivers for both high-side and low-side MOSFETs. It is
therefore important to consider the power that the device is going to dissipate in driving
them in order to avoid exceeding the maximum junction operating temperature.
Two main factors contribute to device power dissipation: bias power and driver power.
●
●
When designing an application based on the L6747A, it is recommended to take into
consideration the effect of external gate resistors on the power dissipated by the driver.
External gate resistors help the device to dissipate the switching power since the same
power P
resulting in a general cooling of the device.
Device power (P
supply pins and is easily quantifiable as follows:
Driver power is the power needed by the driver to continuously switch the external
MOSFETs ON and OFF. It is a function of the switching frequency and total gate
charge of the selected MOSFETs. It can be quantified considering that the total power
P
gate resistance (when present), intrinsic MOSFET resistance, and intrinsic driver
resistance. This last factor is the important one to be determined to calculate the device
power dissipation.
The total power dissipated to switch the MOSFETs is:
P
P
SW
DC
SW
SW
=
dissipated to switch the MOSFETs is influenced by three main factors: external
=
Figure 5
is shared between the internal driver impedance and the external resistor,
V
F
Bootstrap capacitance design
CC
SW
⋅
⋅
I
(
CC
Q
GHS
illustrates some guidelines on how to select the capacitance value for
+
DC
V
) depends on the static consumption of the device through the
PVCC
⋅
PVCC
BOOT
⋅
Doc ID 17126 Rev 1
I
PVCC
+
resistor (in the range of few ohms) may be required in
Q
GLS
⋅
VCC
)
L6747A