Datasheet

L6390 Bootstrap driver
Doc ID 14493 Rev 7 19/26
where Q
gate
is the gate charge of the external Power MOSFET, R
dson
is the on-resistance of
the bootstrap DMOS and T
charge
is the charging time of the bootstrap capacitor.
For example: using a Power MOSFET with a total gate charge of 30 nC, the drop on the
bootstrap DMOS is about 1 V, if the T
charge
is 5 μs. In fact:
Equation 4
V
drop
should be taken into account when the voltage drop on C
BOOT
is calculated: if this drop
is too high, or the circuit topology doesn’t allow a sufficient charging time, an external diode
can be used.
Figure 10. Bootstrap driver
V
drop
30nC
5μs
-------------- -
120Ω 0.7V∼⋅=
TO LOAD
D99IN1067
H.V.
HVG
ab
LVG
HVG
LVG
C
BOOT
TO LOAD
H.V.
C
BOOT
D
BOOT
BOOT
V
CC
V
CC
OUT
OUT
BOOT