Datasheet

L6388E Bootstrap driver
Doc ID 13991 Rev 3 9/19
The following equation is useful to compute the drop on the bootstrap DMOS:
Equation 2
where Q
gate
is the gate charge of the external Power MOSFET, R
DS(on )
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 3
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.
V
drop
I
ch earg
R
dson
V
drop
→
Q
gate
T
ch earg
-------------------
R
dson
==
V
drop
30nC
5μs
----- ----- -----
125Ω 0.8V∼⋅=