L6387
drop on the bootstrap DMOS:
Vdrop = IchargeRdson → Vdrop = TQchgaartgeeRdson
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
Figure 3. Bootstrap Driver.
DMOS is about 1V, if the Tcharge is 5µs. In fact:
Vdrop
=
30nC
5µs
⋅
125Ω
~
0.8V
Vdrop has to be taken into account when the volt-
age 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.
DBOOT
VS
HVG
LVG
a
VBOOT
H.V.
VOUT
VS
CBOOT
TO LOAD
HVG
LVG
b
VBOOT
H.V.
VOUT
CBOOT
TO LOAD
D99IN1056
Figure 4. Turn On Time vs. Temperature
250
@ Vcc = 15V
200
150
Typ.
100
50
0
-45 -25 0
25 50 75 100 125
Tj (°C)
Figure 5. Turn Off Time vs. Temperature
250
@ Vcc = 15V
200
150
Typ.
100
50
0
-45 -25 0
25 50 75 100 125
Tj (°C)
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