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| 型号： | LTC1771ES8#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 11/16页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 8-SOIC |
| 标准包装： | 100 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 占空比： | 100% |
| 电源电压： | 2.8 V ~ 18 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： | -40°C ~ 85°C |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 管件 |
| 产品目录页面： | 1333 (CN2011-ZH PDF) |
LTC1771
APPLICATIO S I FOR ATIO
t ON OFF ? OUT D ? > t ON ( MIN )
? V + V ?
limitingshouldbeaddedtoreducethecurrentinpropor-
tion to the severity of the fault.
Foldback current limiting is implemented by adding two
diodes in series between the output and the I TH pin as
shown in the Functional Diagram. In a hard short (V OUT =
0V) the current will be reduced to approximately 25% of
the maximum output current.
Minimum On-Time Considerations
Minimum on-time t ON(MIN) is the smallest amount of time
that the LTC1771 is capable of turning the top MOSFET on
and off again. It is determined by internal timing delays and
the amount of gate charge required to turn on the
P-channel MOSFET. Low duty cycle applications may
approach this minimum on-time limit and care should be
taken to ensure that:
= t
? V IN ? V OUT ?
where t OFF = 3.5 μ s and t ON(MIN) is generally about 0.4 μ s
for the LTC1771.
As the on-time approaches t ON(MIN) , the LTC1771 will
remain in Burst Mode operation for an increasingly larger
portion of the load range (see Figure 3) and at or below
t ON(MIN) will remain in Burst Mode operation 100% of the
time. The output voltage will continue to be regulated, but
the ripple current and ripple voltage will increase.
100
Mode Pin
Burst Mode operation is disabled by pulling MODE (Pin 8)
below 0.5V. Disabling Burst Mode operation provides a
low noise output spectrum, useful for reducing both audio
and RF interference. It does this by keeping the frequency
constant (for fixed V IN ) down to much lower load current
(1% to 2% of I MAX ) and reducing the amount of output
voltage and current ripple at light loads. When Burst Mode
operation is disabled, efficiency is reduced at light loads
and no load supply current increases to 175 μ A.
Low Supply Operation
Although the LTC1771 can function down to 2.8V, the
maximum allowable output current is reduced when V IN
decreases below 3.2V. Figure 4 shows the amount of
change as the supply is reduced below 3.2V, where 100%
of maximum load equals 0.1/R SENSE . To ensure adequate
output current at V IN < 3.2V, simply lower R SENSE by the
same percentage as the current reduction in Figure 4.
140
120
100
80
60
40
20
0
2.5
3.0
3.5
4.0 4.5
5.0
80
INPUT VOLTAGE (V)
1771 F04
60
40
20
Figure 4. Maximum Load vs Input Voltage
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
0
0
0.5
1.0 1.5
ON-TIME ( μ s)
2.0
2.5
LTC1771. These items are also illustrated graphically in
the layout diagram of Figure 5. Check the following in your
1771 F03
Figure 3. Burst Threshold vs On-Time
layout:
1. Is the Schottky diode closely connected to the drain of
the external MOSFET and the input cap ground?
11
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相关代理商/技术参数 |
参数描述 |
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| LTC1771IS8 | 功能描述:IC REG CTRLR BUCK PWM CM 8-SOIC 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) |
| LTC1771IS8#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 8-SOIC 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:2,000 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:1MHz 占空比:50% 电源电压:9 V ~ 10 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:8-TSSOP（0.173"，4.40mm 宽） 包装:带卷 (TR) |
| LTC1771IS8#TR | 功能描述:IC REG CTRLR BUCK PWM CM 8-SOIC 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) |
| LTC1771IS8#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 8-SOIC 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) |
| LTC1772BES6 | 制造商:Linear Technology 功能描述:IC CTRLR DC/DC S-DWN SOT23-6 |
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