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参数资料
| 型号： | LTC1871EMS#PBF-1 |
| 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： | LEAD FREE, PLASTIC, MSOP-10 |
| 文件页数： | 18/36页 |
| 文件大小： | 354K |
| 代理商： | LTC1871EMS#PBF-1 |
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LTC1871-1
18711fa
APPLICATIO S I FOR ATIO
WU
UU
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 voltage
from a low input voltage) can have very high input cur-
rents, 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 10
μH 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 signifi-
cantly higher than the output current, especially with
smaller inductors and lighter loads. The following formu-
las assume CCM operation and calculate the maximum
peak inductor currents at minimum VIN:
II
VV
V
II
VV
V
L PEAK
O MAX
OD
IN MIN
L PEAK
O MAX
IN MIN
D
IN MIN
1
2
1
2
1
2
()
(
)
()
(
)
()
=+
+
=+
+
χ
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
V
If
D
IN MIN
L
MAX
=
Δ
()
where
II
D
L
O MAX
MAX
:
–
()
Δ = χ
1
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 10
μH inductor with two
windings. With the windings in parallel, 10
μH inductance
is obtained with a current rating of 4A (the number of turns
hasn’t changed, but the wire diameter has doubled).
Splitting the two windings creates two 10
μH inductors
with a current rating of 2A each. Therefore, substituting 2L
yields the following equation for coupled inductors:
LL
V
If
D
IN MIN
L
MAX
12
2
==
Δ
()
Specify the maximum inductor current to safely handle
IL(PK) specified in the equation above. The saturation
current rating for the inductor should be checked at the
minimum input voltage (which results in the highest
inductor current) and maximum output current.
SEPIC Converter: Power MOSFET Selection
The power MOSFET serves two purposes in the LTC1871-
1: it represents the main switching element in the power
path, and its RDS(ON) represents the current sensing
element for the control loop. Important parameters for the
power MOSFET include the drain-to-source breakdown
voltage (BVDSS), the threshold voltage (VGS(TH)), the on-
resistance (RDS(ON)) versus gate-to-source voltage, the
gate-to-source and gate-to-drain charges (QGS and QGD,
respectively), the maximum drain current (ID(MAX)) and
the MOSFET’s thermal resistances (RTH(JC) and RTH(JA)).
The gate drive voltage is set by the 5.2V INTVCC low
dropout regulator. Consequently, logic-level threshold
MOSFETs should be used in most LTC1871-1 applica-
tions. If low input voltage operation is expected (e.g.,
supplying power from a lithium-ion battery), then sublogic-
level threshold MOSFETs should be used.
The maximum voltage that the MOSFET switch must
sustain during the off-time in a SEPIC converter is equal to
the sum of the input and output voltages (VO + VIN). As a
result, careful attention must be paid to the BVDSS speci-
fications for the MOSFETs relative to the maximum actual
switch voltage in the application. Many logic-level devices
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC1871HMS#PBF | 功能描述:IC REG CTRLR BST FLYBK CM 10MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC1871HMS#TRPBF | 功能描述:IC REG CTRLR BST FLYBK CM 10MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC1871HMSPBF | 制造商:Linear Technology 功能描述:PWM Controller Current Mode MSOP10 |
| LTC1871IMS | 功能描述:IC REG CTRLR BST FLYBK CM 10MSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC1871IMS#PBF | 功能描述:IC REG CTRLR BST FLYBK CM 10MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
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