L6390 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6390' PDF : 22 Pages View PDF
Bootstrap driver
L6390
Equation 3
Vdrop
=
Ich argeRdson →Vdrop
=
---Q-----g--a---t--e---
Tch arge
Rds
on
where Qgate is the gate charge of the external power MOS, Rdson is the on resistance of the
bootstrap DMOS and Tcharge is the charging time of the bootstrap capacitor.
For example: using a power MOS with a total gate charge of 30nC the drop on the bootstrap
DMOS is about 1V, if the Tcharge is 5µs. In fact:
Equation 4
Vdrop
=
3----0----n---C---
5µs
⋅
120Ω ∼0.7V
Vdrop has to be taken into account when the voltage drop on CBOOT 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 7. Bootstrap driver
VCC
DBOOT
HVG
LVG
a
BOOT
H.V.
OUT
VCC
CBOOT
TO LOAD
HVG
LVG
b
BOOT
H.V.
OUT
CBOOT
TO LOAD
D99IN1067
18/22
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