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参数资料
| 型号： | LT1871IMS-7#TR |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封装： | PLASTIC, MSOP-10 |
| 文件页数： | 18/32页 |
| 文件大小： | 461K |
| 代理商： | LT1871IMS-7#TR |
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LTC1871-7
25
18717fc
APPLICATIONS INFORMATION
The maximum output voltage for a SEPIC converter is:
VO(MAX) = VIN + VD
() DMAX
1–DMAX
–VD
1
1–DMAX
The maximum duty cycle of the LTC1871-7 is typically
92%.
SEPIC Converter: The Peak and Average
Input Currents
The control circuit in the LTC1871-7 is measuring the input
current (using a sense resistor in the MOSFET source),
so the output current needs to be reected back to the
input in order to dimension the power MOSFET properly.
Based on the fact that, ideally, the output power is equal
to the input power, the maximum input current for a SEPIC
converter is:
IIN(MAX) =IO(MAX)
DMAX
1–DMAX
The peak input current is:
IIN(PEAK) = 1+ 2 IO(MAX)
DMAX
1–DMAX
The maximum duty cycle, DMAX, should be calculated at
minimum VIN.
The constant ‘χ’ represents the fraction of ripple current in
the inductor relative to its maximum value. For example, if
30% ripple current is chosen, then χ = 0.30 and the peak
current is 15% greater than the average.
It is worth noting here that SEPIC converters that operate
at high duty cycles (i.e., that develop a high output volt-
age from a low input voltage) can have very high input
currents, relative to the output current. Be sure to check
that the maximum load current will not overload the input
supply.
SEPIC Converter: Inductor Selection
For most SEPIC applications the equal inductor values
will fall in the range of 10μH to 100μH. Higher values will
reduce the input ripple voltage and reduce the core loss.
Lower inductor values are chosen to reduce physical size
and improve transient response.
Like the boost converter, the input current of the SEPIC
converter is calculated at full load current and minimum
input voltage. The peak inductor current can be signicantly
higher than the output current, especially with smaller in-
ductors and lighter loads. The following formulas assume
CCM operation and calculate the maximum peak inductor
currents at minimum VIN:
IL1(PEAK) = 1+ 2 IO(MAX)
VO + VD
VIN(MIN)
IL2(PEAK) = 1+ 2 IO(MAX)
VIN(MIN) + VD
VIN(MIN)
The ripple current in the inductor is typically 20% to 40%
(i.e., a range of ‘χ’ from 0.20 to 0.40) of the maximum
average input current occurring at VIN(MIN) and IO(MAX) and
ΔIL1 = ΔIL2. Expressing this ripple current as a function of
the output current results in the following equations for
calculating the inductor value:
L =
VIN(MIN)
IL f
DMAX
where
IL = IO(MAX)
DMAX
1–DMAX
By making L1 = L2 and winding them on the same core,
the value of inductance in the equation above is replace
by 2L due to mutual inductance. Doing this maintains the
same ripple current and energy storage in the inductors. For
example, a Coiltronix CTX10-4 is a 10μH inductor with two
windings. With the windings in parallel, 10μH inductance is
obtained with a current rating of 4A (the number of turns
hasn’t changed, but the wire diameter has doubled). Split-
ting the two windings creates two 10μH inductors with a
current rating of 2A each. Therefore, substituting 2L yields
the following equation for coupled inductors:
L1=L2=
VIN(MIN)
2 IL f
DMAX
Specify the maximum inductor current to safely handle
IL(PK)speciedintheequationabove.Thesaturationcurrent
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT1871IMS-7-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Input Voltage,Current Mode Boost, Flyback and SEPIC Controller |
| LT1873-41 | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Optoelectronic |
| LT1873-41UR | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Optoelectronic |
| LT1880 | 制造商:LINER 制造商全称:Linear Technology 功能描述:SOT-23, Rail-to-Rail Output, Picoamp Input Current Precision Op Amp |
| LT1880CS5 | 制造商:Linear Technology 功能描述:OP Amp Single GP R-R O/P ±18V/36V 5-Pin TSOT-23 |
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