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| 型号： | LTC1474IS8-3.3 |
| 厂商： | Linear Technology |
| 文件页数： | 7/20页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 3.3V 0.75A 8SOIC |
| 标准包装： | 100 |
| 类型： | 降压（降压） |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 3.3V |
| 输入电压： | 3 V ~ 18 V |
| PWM 型： | Burst Mode? |
| 电流 - 输出： | 750mA |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 管件 |
| 供应商设备封装： | 8-SOIC |
LTC1474/LTC1475
APPLICATIO N S I N FOR M ATIO N
The basic LTC1474/LTC1475 application circuit is shown
in Figure 1, a high efficiency step-down converter. External
component selection is driven by the load requirement and
begins with the selection of R SENSE . Once R SENSE is
known, L can be chosen. Finally D1, C IN and C OUT are
selected.
R SENSE Selection
The current sense resistor (R SENSE ) allows the user to
program the maximum inductor/switch current to opti-
mize the inductor size for the maximum load. The LTC1474/
LTC1475 current comparator has a maximum threshold of
100mV/(R SENSE + 0.25). The maximum average output
current I MAX is equal to this peak value less half the peak-
to-peak ripple current ? I L .
Allowing a margin for variations in the LTC1474/LTC1475
and external components, the required R SENSE can be
calculated from Figure 2 and the following equation:
ments. Lower peak currents have the advantage of lower
output ripple ( ? V OUT = I PEAK ? ESR), lower noise, and less
stress on alkaline batteries and other circuit components.
Also, lower peak currents allow the use of inductors with
smaller physical size.
Peak currents as low as 10mA can be programmed with
the appropriate sense resistor. Increasing R SENSE above
10 ? , however, gives no further reduction of I PEAK .
For R SENSE values less than 1 ? , it is recommended that
the user parallel standard resistors (available in values ≥
1 ? ) instead of using a special low valued shunt resistor.
Although a single resisor could be used with the desired
value, these low valued shunt resistor types are much
more expensive and are currently not available in case
sizes smaller than 1206. Three or four 0603 size standard
resistors require about the same area as one 1206 size
current shunt resistor at a fraction of the cost.
At higher supply voltages and lower inductances, the peak
R SENSE = (0.067/I MAX ) – 0.25
for 10mA < I MAX < 200mA.
(1)
currents may be slightly higher due to current comparator
overshoot and can be predicted from the second term in
the following equation:
( 2 . 5 ) ?? 10 ? 7 ?? ( V IN OUT )
5
4
FOR LOWEST NOISE
I PEAK =
0 . 1
0 . 25 + R SENSE
+
L
? V
(2)
3
2
1
FOR BEST EFFICIENCY
Note that R SENSE only sets the maximum inductor current
peak. At lower dI/dt (lower input voltages and higher
inductances), the observed peak current at loads less than
I MAX may be less than this calculated peak value due to the
voltage comparator tripping before the current ramps up
0
0
50 100 150 200 250
MAXIMUM OUTPUT CURRENT (mA)
300
high enough to trip the current comparator. This effect
improves efficiency at lower loads by keeping the I 2 R
? 0 . 75 ( V OUT + V D ) t OFF ?
L MIN ≥ ? ?
? ?
? I
I PEAK MAX
1474/75 F02
Figure 2. R SENSE Selection
For I MAX above 200mA, R SENSE is set to zero by shorting
Pins 6 and 7 to provide the maximum peak current of
400mA (limited by the fixed internal sense resistor). This
400mA default peak current can be used for lower I MAX if
desired to eliminate the need for the sense resistor and
associated decoupling capacitor. However, for optimal
performance, the peak inductor current should be set to no
more than what is needed to meet the load current require-
losses down (see Efficiency Considerations section).
Inductor Value Selection
Once R SENSE and I PEAK are known, the inductor value can
be determined. The minimum inductance recommended
as a function of I PEAK and I MAX can be calculated from:
(3)
? ?
where t OFF = 4.75 μ s.
7
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC1474IS8-5 | 功能描述:IC REG BUCK 5V 0.75A 8SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LTC1474IS8-5#PBF | 功能描述:IC REG BUCK 5V 0.75A 8SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LTC1474IS8-5#TR | 功能描述:IC REG BUCK 5V 0.75A 8SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LTC1474IS8-5#TRPBF | 功能描述:IC REG BUCK 5V 0.75A 8SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LTC1474IS8-5PBF | 制造商:Linear Technology 功能描述:DC-DC Converter Step-Down 3-18V SOIC8 |
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