- 您现在的位置：买卖IC网 > PDF目录80172 > LTC3805MPMSE#TRPBF (LINEAR TECHNOLOGY CORP) SWITCHING REGULATOR, 700 kHz SWITCHING FREQ-MAX, PDSO10 PDF资料下载
参数资料
| 型号： | LTC3805MPMSE#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, 700 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封装： | LEAD FREE, PLASTIC, MSOP-10 |
| 文件页数： | 6/20页 |
| 文件大小： | 248K |
| 代理商： | LTC3805MPMSE#TRPBF |
LTC3805
14
3805ff
APPLICATIONS INFORMATION
Feedback in Isolated Applications
Isolated applications do not use the FB pin and error
amplifier but control the ITH pin directly using an opto-
isolator driven on the other side of the isolation barrier as
shown in Figure 5. A detailed version is shown in Figure
9. For isolated converters, the FB pin is grounded which
provides pull-up on the ITH pin. This pull-up is not enough
to properly bias the opto-isolator which is typically 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 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 2)
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 0.020Ω. Note that the instantaneous
peak power in the sense resistor is 0.5W and it must be
rated accordingly. The LTC3805 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 0.020Ω 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
The LTC3805 injects a ramping current through its ISENSE
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’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
sense resistor, effectively reducing the current comparator
threshold in proportion to duty cycle. This stabilizes the
control loop against subharmonic oscillation. The amount
ofreductioninthecurrentcomparatorthreshold(
VSENSE)
can be calculated using the following equation:
VSENSE =
DutyCycle
6%
80%
10A RSLOPE
Note: LTC3805 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 5. Circuit for Isolated Feedback
LTC3805
ITH
FB
VCC
ISOLATION
BARRIER
GND
3805 F05
相关PDF资料 |
PDF描述 |
|---|---|
| LM4040BIM3-5.0T&R | 1-OUTPUT TWO TERM VOLTAGE REFERENCE, 5 V, PDSO3 |
| LRB5D | 2-OUTPUT 5 W DC-DC REG PWR SUPPLY MODULE |
| LRB9S | 1-OUTPUT 5 W DC-DC REG PWR SUPPLY MODULE |
| LRC24D | 2-OUTPUT 5 W DC-DC REG PWR SUPPLY MODULE |
| LH1601-2RD8 | 1-OUTPUT 70 W AC-DC REG PWR SUPPLY MODULE |
相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3806EDE | 功能描述:IC REG CTRLR FLYBACK PWM 12-DFN RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3806EDE#PBF | 功能描述:IC REG CTRLR FLYBACK PWM 12-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3806EDE#TR | 功能描述:IC REG CTRLR FLYBACK PWM 12-DFN RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3806EDE#TRPBF | 功能描述:IC REG CTRLR FLYBACK PWM 12-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3808EDE | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Sync Step Down 2.75V to 9.8V Input 14-Pin DFN EP |
发布紧急采购，3分钟左右您将得到回复。