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参数资料
| 型号： | LTC3805EDD-5#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 15/20页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST FLYBK PWM 10DFN |
| 标准包装： | 2,500 |
| 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 ~ 85°C |
| 封装/外壳： | 10-WFDFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 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 |
LTC3805-5
APPLICATIONS INFORMATION
V OC =
R SENSE1 + R SENSE2
V OC =
R1 + R2
t SS(EXT) = C SS
t FTO(EXT) = C SS
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 6 and 7 show two
ways to do this. Figure 6 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 .
For larger currents, values of the current sense resistors
must be very small and the circuit of Figure 6 becomes
impractical. The circuit of Figure 7 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 10 W
to prevent the I OC = 10μA threshold adjustment current
from producing a shift in V OC .
GATE
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 internal
soft-start time t SS(IN) = 1.8ms.
If there is an overcurrent fault detected on the OC pin, the
LTC3805-5 enters a shutdown mode while a 2μA current
discharges the voltage on the SSFLT pin from 4.75V to
about 0.7V. The fault timeout t FTO(EXT) is therefore:
4.75V ? 0.7V
2μA
At this point, the LTC3805-5 attempts a restart.
In the event of a persistent fault, such as a short-circuit
on the converter output, the converter enters a “hiccup”
mode where it continues to try and restart at repetition
rate determined by C SS . If the fault is eventually removed
the converter successfully restarts.
GATE
LTC3805-5
I SENSE
R SLOPE
I SLOPE
LTC3805-5
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
38055 F06
GND
38055 F07
Figure 6. Circuit to Increase the Overcurrent
Threshold for Small Switch Currents
Figure 7. Circuit to Increase the Overcurrent
Threshold for Large Switch Currents
38055fe
15
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3805EMSE | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Sync Flyback 8.8V to 75V Input 10-Pin MSOP EP |
| LTC3805EMSE#PBF | 功能描述:IC REG CTRLR BST FLYBK CM 10MSOP 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) |
| LTC3805EMSE#TRPBF | 功能描述:IC REG CTRLR BST FLYBK CM 10MSOP 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) |
| LTC3805EMSE-5#PBF | 功能描述:IC REG CTRLR BST FLYBK CM 10MSOP 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) |
| LTC3805EMSE-5#PBF | 制造商:Linear Technology 功能描述:IC, FLYBACK/ BOOST/SEPIC CTRL, MSOP-10 |
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