L6743_08 STMICROELECTRONICS [STMicroelectronics], L6743_08 Datasheet - Page 9

• Manufacturer Part Number: L6743_08
• Description: High current MOSFET driver
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

L6743, L6743Q
5.3
5.4
Internal BOOT diode
L6743, L6743Q embeds a boot diode to supply the high-side driver saving the use of an
external component. Simply connecting an external capacitor between BOOT and PHASE
complete the high-side supply connections.
To prevent bootstrap capacitor to extra-charge as a consequence of large negative spikes,
an external series resistance R
BOOT pin.
Bootstrap capacitor needs to be designed in order to show a negligible discharge due to the
high-side MOSFET turn-on. In fact it must give a stable voltage supply to the high-side driver
during the MOSFET turn-on also minimizing the power dissipated by the embedded Boot
Diode.
bootstrap according to the desired discharge and depending on the selected MOSFET.
Figure 5.
Power dissipation
L6743, L6743Q embeds high current drivers for both high-side and low-side MOSFETs: it is
then important to consider the power that the device is going to dissipate in driving them in
order to avoid overcoming the maximum junction operative temperature.
Two main terms contribute in the device power dissipation: bias power and drivers' power.
●
●
Device power (P
supply pins and it is simply quantifiable as follow:
Drivers' power is the power needed by the driver to continuously switch ON and OFF
the external MOSFETs; 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
dissipated to switch the MOSFETs dissipated by three main factors: external gate
resistance (when present), intrinsic MOSFET resistance and intrinsic driver resistance.
This last term is the important one to be determined to calculate the device power
dissipation.
The total power dissipated to switch the MOSFETs results:
P
P
DC
SW
Figure 5
=
=
V
F
Bootstrap capacitance design
CC
SW
gives some guidelines on how to select the capacitance value for the
⋅
⋅
I
(
CC
Q
GHS
+
DC
V
) depends on the static consumption of the device through the
PVCC
⋅
PVCC
⋅
I
BOOT
PVCC
+
Q
GLS
(in the range of few ohms) may be required in series to
⋅
VCC
)
Device description and operation
SW
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