參數(shù)資料
型號(hào)： LT3845EFE#TR
廠商： LINEAR TECHNOLOGY CORP
元件分類(lèi)： 穩(wěn)壓器
英文描述： SWITCHING CONTROLLER, 600 kHz SWITCHING FREQ-MAX, PDSO16
封裝： 4.40 MM, PLASTIC, TSSOP-16
文件頁(yè)數(shù)： 2/24頁(yè)
文件大?。?/td> 263K
代理商： LT3845EFE#TR
LT3845
10
3845fb
where QG(TOTAL) is the total MOSFET gate charge of the
TG and BG.
In applications where these conditions are exceeded, VCC
must be derived from an external source after start-up.
Maximum continuous regulator power dissipation may be
exceeded for short duration VIN transients.
In LT3845 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 voltage.
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.
Burst Mode
The LT3845 employs low current Burst Mode functional-
ity to maximize efciency during no load and low load
conditions. Burst Mode operation is enabled by shorting
the BURST_EN pin to SGND. Burst Mode operation can be
disabled by shorting BURST_EN to either VFB or VCC.
When the required switch current, sensed via the VC
pin voltage, is below 15% of maximum, the Burst Mode
operation is employed and that level of sense current is
latched onto the IC control path. If the output load requires
less than this latched current level, the converter will
overdrive the output slightly during each switch cycle.
This overdrive condition is sensed internally and forces
the voltage on the VC pin to continue to drop. When the
voltage on VC drops 150mV below the 15% load level,
switching is disabled and the LT3845 shuts down most
of its internal circuitry, reducing total quiescent current
to 120μA. When the converter output begins to fall, the
VC pin voltage begins to climb. When the voltage on the
VC pin climbs back to the 15% load level, the IC returns
to normal operation and switching resumes. An internal
clamp on the VC pin is set at 100mV below the switch
disable threshold, which limits the negative excursion of
the pin voltage, minimizing the converter output ripple
during Burst Mode operation.
During Burst Mode operation, VIN pin current is 20μA and
VCC current is reduced to 100μA. If no external drive is
provided for VCC, all VCC bias currents originate from the
APPLICATIONS INFORMATION
VOUT
1
μF
B0520
1
μF
Si1555DL
LT3845
Charge Pump Doubler
Charge Pump Tripler
VCC
BG
VOUT
1
μF
B0520
1
μF
1
μF
Si1555DL
LT3845
VCC
BG
B0520
3845 AI01
TG
VOUT
3845 AI04
VCC
SW
BG
N
LT3845
Inductor Auxiliary Winding
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