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参数资料
| 型号： | LTC3805HMSE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 16/20页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST FLYBK CM 10MSOP |
| 标准包装： | 50 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 700kHz |
| 占空比： | 95% |
| 电源电压： | 3.95 V ~ 75 V |
| 降压： | 无 |
| 升压： | 是 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 150°C |
| 封装/外壳： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 |
| 包装： | 管件 |
| 产品目录页面： | 1336 (CN2011-ZH PDF) |
| 相关产品： | 732-2264-6-ND - TRANS FLYBACK LTC3805 36.3UH 732-2264-1-ND - TRANS FLYBACK LTC3805 36.3UH 732-2264-2-ND - TRANS FLYBACK LTC3805 36.3UH |
LTC3805
APPLICATIONS INFORMATION
V OC =
R1 + R2
t SS(EXT) = C SS
V OC =
R SENSE1 + R SENSE2
beslowedbyusingalargervalueofSSFLTcapacitor.Itis
also possible to trip overcurrent protection during a load
step especially if the trip threshold is lowered by making
R OC > R OC(CRIT) .
Another overcurrent protection strategy is keep the
converter running as current limiting reduces the duty
cycle and the output voltage sags. In this case, the goal
is often keep the converter in normal operation over as
wide a range as possible, including current limiting, and
to trigger the overcurrent trip only to prevent damage. To
implement this strategy use a value of R OC smaller than
R OC(CRIT) . This also reduces sensitivity to overcurrent trips
caused by transient operation. In the limit, set R OC = 0
and connect the OC pin directly to R SENSE . This causes an
overcurrent trip near minimum duty cycle or around 6%.
In some cases it may be desirable to increase the trip
threshold even further. In this strategy, the converter is
allowed to operate all the way down to minimum duty
cycle at which point the cycle-by-cycle current limit of
the I SENSE pin is lost and switch current goes up propor-
tionally to the output current. Figures 7 and 8 show two
ways to do this. Figure 7 is for relatively low currents with
relatively large values of R SENSE . Using this circuit the
overcurrent trip threshold is increased from 100mV to:
100mV
R SENSE1
where it is assumed that the values of R SENSE1 and
R SENSE2 are so small that the I OC = 10μA threshold adjust-
ment current produces a negligible change in V OC .
GATE
For larger currents, values of the current sense resistors
must be very small and the circuit of Figure 7 becomes
impractical. The circuit of Figure 8 can be substituted and
the current sense threshold is increased from 100mV to:
100mV
R1
where the values of R1 and R2 should be kept below 10Ω
to prevent the I OC = 10μA threshold adjustment current
from producing a shift in V OC .
External Soft-Start Fault Timeout
The external soft-start is programmed by a capacitor C SS
from the SSFLT pin to GND. At the initiation of soft-start
the voltage on the SSFLT pin is quickly charged to 0.7V
at which point GATE begins switching. From that point,
a 6μA current charges the voltage on the SSFLT pin until
the voltage reaches about 2.25V at which point soft-start
is over and the converter enters closed-loop regulation.
The soft-start time t SS(EXT) as a function of the soft-start
capacitor, C SS , is therefore:
2.25 ? 0.7V
6μA
After soft-start is complete, the voltage on the SSFLT
pin continues to charge to about a final value of 4.75V.
Note that choosing a value of C SS less than 5.8nF has
no effect since it would attempt to program an external
soft-start time t SS(EXT) less than the mandatory minimum
GATE
LTC3805
I SENSE
R SLOPE
I SLOPE
LTC3805
I SENSE
R SLOPE
I SLOPE
OC
I OC = 10 μ A
R SENSE2
OC
I OC = 10 μ A
R2
R SENSE1
R1
R SENSE
GND
3805 F07
GND
3805 F08
Figure 7. Circuit to Increase the Overcurrent
Threshold for Small Switch Currents
Figure 8. Circuit to Increase the Overcurrent
Threshold for Large Switch Currents
3805fg
16
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| LTC3805IDD#PBF | 功能描述:IC REG CTRLR BST FLYBK PWM 10DFN 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) |
| LTC3805IDD#TRPBF | 功能描述:IC REG CTRLR BST FLYBK PWM 10DFN 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) |
| LTC3805IDD-5#PBF | 功能描述:IC REG CTRLR BST FLYBK PWM 10DFN 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) |
| LTC3805IDD-5#TRPBF | 功能描述:IC REG CTRLR BST FLYBK PWM 10DFN 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) |
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