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参数资料
| 型号： | LT3845MPFE#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 11/26页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 16TSSOP |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 500kHz |
| 电源电压： | 4 V ~ 60 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -55°C ~ 125°C |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 包装： | 带卷 (TR) |
LT3845
APPLICATIONS INFORMATION
where Q G(TOTAL) is the total MOSFET gate charge of the
TG and BG.
Inductor Auxiliary Winding
In applications where these conditions are exceeded, V CC
must be derived from an external source after start-up.
Maximum continuous regulator power dissipation may be
exceeded for short duration V IN transients.
TG
SW
LT3845
V CC
?
N
V OUT
In LT3845 converter applications with output voltages in
?
the 9V to 20V range, back-feeding V CC and V BOOST from
the converter output is trivial, accomplished by connect-
ing diodes from the output to these supply pins. Deriving
BG
3845 AI04
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 V CC 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.
Charge Pump Doubler
V OUT
Burst Mode
The LT3845 employs low current Burst Mode functional-
ity to maximize ef?ciency 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 V FB or V CC .
When the required switch current, sensed via the V C
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
LT3845
V CC
1μF
B0520
B0520
1μF
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 V C pin to continue to drop. When the
BG
Si1555DL
Charge Pump Tripler
voltage on V C 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
B0520
B0520
1μF
V OUT
V C pin voltage begins to climb. When the voltage on the
V C pin climbs back to the 15% load level, the IC returns
to normal operation and switching resumes. An internal
LT3845
V CC
B0520
1μF
1μF
Si1555DL
Si1555DL
clamp on the V C 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.
BG
3845 AI01
During Burst Mode operation, V IN pin current is 20μA and
V CC current is reduced to 100μA. If no external drive is
provided for V CC , all V CC bias currents originate from the
3845fd
11
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3846 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Current Mode PWM Controller |
| LT3846J | 制造商:Linear Technology 功能描述:Current Mode PWM Controller 200mA 16-Pin CDIP |
| LT3846N | 制造商:LINER 制造商全称:Linear Technology 功能描述:Current Mode PWM Controller |
| LT3847 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Current Mode PWM Controller |
| LT3847J | 制造商:Linear Technology 功能描述:Current Mode PWM Controller 200mA 16-Pin CDIP |
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