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| 型号： | LT3970HMS-3.3#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/22页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 3.3V 0.35A 10MSOP |
| 标准包装： | 2,500 |
| 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： | 4.2 V ~ 40 V |
| PWM 型： | 电流模式，Burst Mode? |
| 频率 - 开关： | 200kHz ~ 2.25MHz |
| 电流 - 输出： | 350mA |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 10-MSOP |
LT3970 Series
APPLICATIONS INFORMATION
R1 = R2 ? OUT – 1 ?
FBResistorNetwork
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the 1% resis-
tors according to:
? V ?
? 1.21 ?
Reference designators refer to the Block Diagram. Note
that choosing larger resistors will decrease the quiescent
current of the application circuit.
Setting the Switching Frequency
The LT3970 uses a constant frequency PWM architecture
that can be programmed to switch from 200kHz to 2.2MHz
by using a resistor tied from the RT pin to ground. A table
showing the necessary R T value for a desired switching
frequency is in Table 1.
Table 1. Switching Frequency vs R T Value
SWITCHING FREQUENCY (MHz) R T VALUE (kΩ)
where V IN is the typical input voltage, V OUT is the output
voltage, V D is the integrated catch diode drop (~0.7V),
and V SW is the internal switch drop (~0.5V at max load).
This equation shows that slower switching frequency is
necessary to accommodate high V IN /V OUT ratio.
Lower frequency also allows a lower dropout voltage. The
input voltage range depends on the switching frequency
because the LT3970 switch has finite minimum on and off
times. The switch can turn on for a minimum of ~150ns and
turn off for a minimum of ~160ns (note that the minimum
on-time is a strong function of temperature). This means
that the minimum and maximum duty cycles are:
DC MIN = f SW ? t ON(MIN)
DC MAX = 1 – f SW ? t OFF(MIN)
where f SW is the switching frequency, the t ON(MIN) is the
minimum switch on-time (~150ns), and the t OFF(MIN) is
the minimum switch off-time (~160ns). These equations
show that duty cycle range increases when switching
frequency is decreased.
0.2
0.3
0.4
0.5
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
768
499
357
280
226
158
124
100
80.6
68.1
57.6
49.9
42.2
A good choice of switching frequency should allow ad-
equate input voltage range (see next section) and keep
the inductor and capacitor values small.
Input Voltage Range
The minimum input voltage is determined by either the
LT3970’s minimum operating voltage of 4.2V or by its
maximum duty cycle (as explained in previous section).
The minimum input voltage due to duty cycle is:
f SW(MAX) =
V OUT + V D
V IN(MIN) = – V D + V SW
OperatingFrequencyTrade-Offs
Selection of the operating frequency is a trade-off between
efficiency, component size, minimum dropout voltage and
maximum input voltage. The advantage of high frequency
operation is that smaller inductor and capacitor values may
be used. The disadvantages are lower efficiency, lower
maximum input voltage, and higher dropout voltage. The
highest acceptable switching frequency (f SW(MAX) ) for a
given application can be calculated as follows:
V OUT + V D
t ON(MIN) ( V IN – V SW + V D )
10
1 – f SW ? t OFF(MIN)
where V IN(MIN) is the minimum input voltage, V OUT is the
output voltage, V D is the catch diode drop (~0.7V), V SW
is the internal switch drop (~0.5V at max load), f SW is
the switching frequency (set by RT), and t OFF(MIN) is the
minimum switch off-time (160ns). Note that higher switch-
ing frequency will increase the minimum input voltage.
If a lower dropout voltage is desired, a lower switching
frequency should be used.
3970fc
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| LT3970HMS-5#PBF | 功能描述:IC REG BUCK 5V 0.35A 10MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT3970HMS-5#TRPBF | 功能描述:IC REG BUCK 5V 0.35A 10MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
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| LT3970HMS-5-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:40V, 350mA Step-Down Regulator with 2.5μA Quiescent Current and Integrated Diodes |
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