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| 型号： | LT3470IDDB#TRMPBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/20页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 0.2A 8DFN |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 1.25 V ~ 16 V |
| 输入电压： | 4 V ~ 40 V |
| PWM 型： | Burst Mode? |
| 电流 - 输出： | 200mA |
| 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： | 8-WFDFN 裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 8-DFN（3x2） |
| 其它名称： | LT3470IDDB#TRMPBFDKR |
LT3470
APPLICATIONS INFORMATION
V OUT + V D
V IN – V SW + V D
( 1– DC ) ( V D + V OUT )
L ? ? I L
InputVoltageRange
The minimum input voltage required to generate a par-
ticular output voltage in an LT3470 application is limited
by either its 4V undervoltage lockout or by its maximum
duty cycle. The duty cycle is the fraction of time that the
internal switch is on and is determined by the input and
output voltages:
DC =
where V D is the forward voltage drop of the catch diode
(~0.6V) and V SW is the voltage drop of the internal switch
at maximum load (~0.4V). Given DC MAX = 0.90, this leads
to a minimum input voltage of:
where V IN(MAX) is the maximum input voltage for the ap-
plication, t ON-TIME(MIN) is ~150ns and I MAX is the maximum
allowable increase in switch current during a minimum
switch on-time (150mA). While this equation provides a
safe inductor value, the resulting application circuit may
switch at too high a frequency to yield good efficiency.
It is advised that switching frequency be below 1.2MHz
during normal operation:
f =
where f is the switching frequency, ? I L is the ripple current
in the inductor (~150mA), V D is the forward voltage drop
of the catch diode, and V OUT is the desired output voltage.
V IN(MIN) = ? OUT
? V + V D ?
? DC MAX ? ?
+ V SW – V D
If the application circuit is intended to operate at high duty
cycles (V IN close to V OUT ), it is important to look at the
calculated value of the switch off-time:
t OFF-TIME =
L MIN =
Thisanalysisassumestheparthasstartedupsuchthatthe
capacitor tied between the BOOST and SW pins is charged
to more than 2V. For proper start-up, the minimum input
voltage is limited by the boost circuit as detailed in the
section BOOST Pin Considerations.
The maximum input voltage is limited by the absolute
maximum V IN rating of 40V, provided an inductor of suf-
ficient value is used.
Inductor Selection
The switching action of the LT3470 during continuous
operation produces a square wave at the SW pin that
results in a triangle wave of current in the inductor. The
hysteretic mode control regulates the top and bottom
current limits (see Electrical Characteristics) such that
the average inductor current equals the load current. For
safe operation, it must be noted that the LT3470 cannot
turn the switch on for less than ~150ns. If the inductor is
small and the input voltage is high, the current through the
switch may exceed safe operating limit before the LT3470
is able to turn off. To prevent this from happening, the
following equation provides a minimum inductor value:
V IN(MAX) ? t ON-TIME(MIN)
I MAX
1– DC
f
The calculated t OFF-TIME should be more than LT3470’s
minimum t OFF-TIME (See Electrical Characteristics), so
the application circuit is capable of delivering full rated
output current. If the full output current of 200mA is not
required, the calculated t OFF-TIME can be made less than
minimum t OFF-TIME possibly allowing the use of a smaller
inductor. See Table 1 for an inductor value selection guide.
Table 1. Recommended Inductors for Loads up to 200mA
V OUT V IN UP TO 16V V IN UP TO 40V
2.5V 10μH 33μH
3.3V 10μH 33μH
5V 15μH 33μH
12V 33μH 47μH
Choose an inductor that is intended for power applications.
Table 2 lists several manufacturers and inductor series.
For robust output short-circuit protection at high V IN (up
to 40V) use at least a 33μH inductor with a minimum
450mA saturation current. If short-circuit performance is
not required, inductors with I SAT of 300mA or more may
3470fd
9
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| LT3470ITS8#TRM | 制造商:Linear Technology 功能描述:Conv DC-DC Single Step Down 4V to 40V 8-Pin TSOT-23 T/R |
| LT3470ITS8#TRMPBF | 功能描述:IC REG BUCK ADJ 0.2A TSOT23-8 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:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 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:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
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