L6398 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6398' PDF : 16 Pages View PDF
Bootstrap driver
L6398
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 1 V, if the Tcharge is 5 μs. In fact:
Equation 4
Vdrop = 3---5-0--μ--n--s-C--- ⋅ 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 6. Bootstrap driver with high voltage fast recovery diode
VCC
DBOOT
HVG
LVG
BOOT
H.V.
OUT
CBOOT
TO LOAD
Figure 7. Bootstrap driver with internal charge pump
BOOT
VCC
H.V.
HVG
OUT
CBOOT
TO LOAD
LVG
12/16
Doc ID 18199 Rev 3
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