LT3800 데이터 시트보기 (PDF) - Linear Technology
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LT3800 Datasheet PDF : 24 Pages
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APPLICATIO S I FOR ATIO
The onboard VCC regulator will provide gate drive power for
start-up under all conditions with total MOSFET gate charge
loads up to 180nC. The regulator can operate the LT3800
continuously, provided the VIN voltage and/or MOSFET gate
charge currents do not create excessive power dissipation
in the IC. Safe operating conditions for continuous regu-
lator use are shown in Figure 1. In applications where these
conditions are exceeded, VCC must be derived from an
external source after start-up.
70
60
50
40
30
20
SAFE
OPERATING
CONDITIONS
10
0
50
100
150
200
TOTAL FET GATE CHARGE (nC)
3800 F01
Figure 1. VCC Regulator Continuous Operating Conditions
In LT3800 converter applications with output voltages in
the 9V to 20V range, back-feeding VCC and VBOOST from
the converter output is trivial, accomplished by connect-
ing diodes from the output to these supply pins. Deriving
these supplies from output voltages greater than 20V will
require additional regulation to reduce the feedback volt-
age. Outputs lower than 9V will require step-up techniques
to increase the feedback voltage to something greater than
the 8V VCC regulated output. Low power boost switchers
are sometimes used to provide the step-up function, but
a simple charge-pump can perform this function in many
instances.
LT3800
Charge Pump Doubler
VCC
LT3800
B0520
1µF
VOUT
B0520
1µF
BG
Si1555DL
Charge Pump Tripler
B0520 B0520 1µF
VOUT
VCC
LT3800
BG
B0520 1µF
1µF
Si1555DL
Si1555DL
3800 AI01
Inductor Auxiliary Winding
TG
SW
LT3800
VCC
BG
•N
VOUT
•
3800 AI04
3800fb
9
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