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參數(shù)資料
| 型號： | LT3470AIDDB#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 0.56 A SWITCHING REGULATOR, PDSO8 |
| 封裝： | 3 X 2 MM, 0.75 MM HEIGHT, LEAD FREE, PLASTIC, MO-229WECD-1, DFN-8 |
| 文件頁數(shù)： | 20/20頁 |
| 文件大?。?/td> | 197K |
| 代理商： | LT3470AIDDB#PBF |
LT3470A
9
3470afb
Input Voltage Range
The minimum input voltage required to generate a par-
ticular output voltage in an LT3470A 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 =
VOUT + VD
VIN –VSW + VD
where VD is the forward voltage drop of the catch diode
(~0.6V) and VSW is the voltage drop of the internal switch
at maximum load (~0.4V). Given DCMAX = 0.90, this leads
to a minimum input voltage of:
VIN(MIN) =
VOUT + VD
DCMAX
+ VSW –VD
This analysis assumes the part has started up such that the
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 VIN rating of 40V, provided an inductor of suf-
ficient value is used.
Inductor Selection
The switching action of the LT3470A 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 induc-
tor current equals the load current. For safe operation, it
must be noted that the LT3470A 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 LT3470A is able to
turn off. To prevent this from happening, the following
equation provides a minimum inductor value:
LMIN =
VIN(MAX) tON-TIME(MIN)
IMAX
APPLICATIONS INFORMATION
where VIN(MAX) is the maximum input voltage for the ap-
plication, tON-TIME(MIN)is ~150ns and IMAX 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 =
1– DC
() VD + VOUT
()
L ΔIL
where f is the switching frequency, ΔIL is the ripple current
in the inductor (~200mA), VD is the forward voltage drop
of the catch diode, and VOUT is the desired output voltage.
If the application circuit is intended to operate at high duty
cycles (VIN close to VOUT), it is important to look at the
calculated value of the switch off-time:
tOFF-TIME =
1– DC
f
The calculated tOFF-TIME should be more than LT3470A’s
minimum tOFF-TIME (See Electrical Characteristics), so the
application circuit is capable of delivering full rated output
current. If the full output current of 250mA is not required,
the calculated tOFF-TIME can be made less than minimum
tOFF-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 250mA
VOUT
VIN Up to 16V
VIN 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 VIN (up
to 40V) use at least a 33μH inductor with a minimum
450mA saturation current. If short-circuit performance is
not required, inductors with ISAT of 300mA or more may
be used. It is important to note that inductor saturation
current is reduced at high temperatures—see inductor
vendors for more information.
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|---|---|
| LT3470AIDDB-TRPBF | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Micropower Buck Regulator with Integrated Boost and Catch Diodes |
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| LT3470EDDB#TRMPBF | 功能描述:IC REG BUCK ADJ 0.2A 8DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標準包裝:2,500 系列:- 類型:升壓（升壓） 輸出類型:可調(diào)式 輸出數(shù):1 輸出電壓:1.24 V ~ 30 V 輸入電壓:1.5 V ~ 12 V PWM 型:電流模式，混合 頻率 - 開關(guān):600kHz 電流 - 輸出:500mA 同步整流器:無 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:8-SOIC |
| LT3470EDDB#TRPBF | 功能描述:IC REG BUCK ADJ 0.2A 8DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標準包裝:2,500 系列:- 類型:升壓（升壓） 輸出類型:可調(diào)式 輸出數(shù):1 輸出電壓:1.24 V ~ 30 V 輸入電壓:1.5 V ~ 12 V PWM 型:電流模式，混合 頻率 - 開關(guān):600kHz 電流 - 輸出:500mA 同步整流器:無 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:8-SOIC |
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