l6391n STMicroelectronics, l6391n Datasheet - Page 17

• Manufacturer Part Number: l6391n
• Description: High-voltage High And Low Side Driver
• Manufacturer: STMicroelectronics

L6391
The following equation is useful to compute the drop on the bootstrap DMOS:
Equation 3
where Q
bootstrap DMOS and T
For example: using a power MOS with a total gate charge of 30nC the drop on the bootstrap
DMOS is about 1 V, if the T
Equation 4
V
is too high, or the circuit topology doesn’t allow a sufficient charging time, an external diode
can be used.
Figure 8.
Figure 9.
drop
has to be taken into account when the voltage drop on C
gate
is the gate charge of the external power MOS, R
Bootstrap driver with high voltage fast recovery diode
Bootstrap driver with internal charge pump
V
drop
V
V
CC
CC
charge
=
charge
I
V
is the charging time of the bootstrap capacitor.
ch
Doc ID 17892 Rev 1
drop
D
arg
BOOT
is 5 μs. In fact:
e
R
=
b
dson
HVG
LVG
HVG
30nC
-------------- - 120Ω
LVG
5μs
→
⋅
V
drop
BOOT
OUT
BOOT
OUT
=
∼
H.V.
H.V.
------------------ R
T
0.7V
Q
ch
dson
gate
BOOT
arg
C
C
TO LOAD
TO LOAD
e
is the on resistance of the
BOOT
BOOT
is calculated: if this drop
dson
Bootstrap driver
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