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參數(shù)資料
| 型號： | LTC3805HMSE-5#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, 700 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封裝： | LEAD FREE, PLASTIC, MSOP-10 |
| 文件頁數(shù)： | 5/20頁 |
| 文件大?。?/td> | 265K |
| 代理商： | LTC3805HMSE-5#TRPBF |
LTC3805-5
38055fd
applications inForMation
Feedback in Isolated Applications
IsolatedapplicationsdonotusetheFBpinanderrorampli-
fier but control the ITH pin directly using an opto-isolator
driven on the other side of the isolation barrier as shown
in Figure 4. For isolated converters, the FB pin is grounded
which provides pull-up on the ITH pin. This pull-up is not
enoughtoproperlybiastheopto-isolatorwhichistypically
biased using a resistor to VCC. Since the ITH pin cannot
sink the opto-isolator bias current, a diode is required to
block it from the ITH pin. A low leakage Schottky diode,
or low forward voltage PN junction diode, should be used
to ensure that the opto-isolator is able to pull ITH down
to its lower clamp.
Oscillator Synchronization
The oscillator may be synchronized to an external clock
by connecting the synchronization signal to the SYNC pin.
The LTC3805-5 oscillator and turn-on of the switch are
synchronized to the rising edge of the external clock. The
frequency of the external sync signal must be ±33% with
respect to fOSC (as programmed by RFS). Additionally, the
value of fSYNC must be between 70kHz and 700kHz.
Current Sense Resistor Considerations
The external current sense resistor (RSENSE in Figure 8)
allows the user to optimize the current limit behavior for
the particular application. As the current sense resistor
is varied from several ohms down to tens of milliohms,
peak switch current goes from a fraction of an ampere to
several amperes. Care must be taken to ensure proper
circuit operation, especially with small current sense
resistor values.
Forexample,withthepeakcurrentsensevoltageof100mV
on the ISENSE pin, a peak switch current of 5A requires
a sense resistor of 0.020
W. Note that the instantaneous
peak power in the sense resistor is 0.5W and it must be
rated accordingly. The LTC3805-5 has only a single sense
line to this resistor. Therefore, any parasitic resistance
in the ground side connection of the sense resistor will
increase its apparent value. In the case of a 0.020
W sense
resistor, one milliohm of parasitic resistance will cause a
5% reduction in peak switch current. So the resistance of
printed circuit copper traces and vias cannot necessarily
be ignored.
Programmable Slope Compensation
TheLTC3805-5injectsarampingcurrentthroughitsISENSE
pin into an external slope compensation resistor RSLOPE.
This current ramp starts at zero right after the GATE pin
has been high for the LTC3805-5’s minimum duty cycle
of 6%. The current rises linearly towards a peak of 10A
at the maximum duty cycle of 80%, shutting off once the
GATEpingoeslow.AseriesresistorRSLOPEconnectingthe
ISENSE pin to the current sense resistor RSENSE develops a
ramping voltage drop. From the perspective of the ISENSE
pin, this ramping voltage adds to the voltage across the
senseresistor,effectivelyreducingthecurrentcomparator
threshold in proportion to duty cycle. This stabilizes the
control loop against subharmonic oscillation. The amount
ofreductioninthecurrentcomparatorthreshold(
DVSENSE)
can be calculated using the following equation:
DVSENSE =
DutyCycle
6%
80%
10A RSLOPE
Note: LTC3805-5 enforces 6% < Duty Cycle < 80%. A good
starting value for RSLOPE is 3k, which gives a 30mV drop
in current comparator threshold at 80% duty cycle.
Designs that do not operate at greater than 50% duty cycle
do not need slope compensation and may replace RSLOPE
with a direct connection.
Figure 4. Circuit for Isolated Feedback
LTC3805-5
ITH
FB
VCC
ISOLATION
BARRIER
GND
38055 F04
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參數(shù)描述 |
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| LTC3805IDD#PBF | 功能描述:IC REG CTRLR BST FLYBK PWM 10DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC3805IDD#TRPBF | 功能描述:IC REG CTRLR BST FLYBK PWM 10DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC3805IDD-5#PBF | 功能描述:IC REG CTRLR BST FLYBK PWM 10DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC3805IDD-5#TRPBF | 功能描述:IC REG CTRLR BST FLYBK PWM 10DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC3805IMSE#PBF | 功能描述:IC REG CTRLR BST FLYBK CM 10MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
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