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| 型号： | LTC1871EMS |
| 厂商： | Linear Technology |
| 文件页数： | 26/36页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST FLYBK CM 10MSOP |
| 标准包装： | 50 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 1MHz |
| 占空比： | 97% |
| 电源电压： | 2.5 V ~ 36 V |
| 降压： | 无 |
| 升压： | 是 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽） |
| 包装： | 管件 |
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LTC1871
APPLICATIONS INFORMATION
I O(MAX)
1 + ? V O + V D
T + 1
V IN(MIN)
P FET = I O(MAX) ?
? R DS(ON) ? D MAX ?
1– D MAX
( ) 1.85 ?I O(MAX) ? 1– MAX ? C RSS ? f
+ k ? V IN(MIN) + V O
During the MOSFET’s on-time, the control circuit limits
the maximum voltage drop across the power MOSFET to
about 150mV (at low duty cycle). The peak inductor current
is therefore limited to 150mV/R DS(ON) . The relationship
between the maximum load current, duty cycle and the
R DS(ON) of the power MOSFET is:
V SENSE(MAX) 1 1
R DS(ON) ? ?
2
The V SENSE(MAX) term is typically 150mV at low duty cycle
and is reduced to about 100mV at a duty cycle of 92% due
to slope compensation, as shown in Figure 8. The constant
‘ χ ’ in the denominator represents the ripple current in the
inductors relative to their maximum current. For example,
if 30% ripple current is chosen, then χ = 0.30. The ρ T term
accounts for the temperature coef?cient of the R DS(ON) of
the MOSFET, which is typically 0.4%/°C. Figure 9 illustrates
the variation of normalized R DS(ON) over temperature for
a typical power MOSFET.
Another method of choosing which power MOSFET to
use is to check what the maximum output current is for a
given R DS(ON) since MOSFET on-resistances are available
The power dissipated by the MOSFET in a SEPIC converter
is:
2
D MAX
T
D
The ?rst term in the equation above represents the I 2 R
losses in the device and the second term, the switching
losses. The constant k = 1.7 is an empirical factor inversely
related to the gate drive current and has the dimension
of 1/current.
From a known power dissipated in the power MOSFET, its
junction temperature can be obtained using the following
formula:
T J = T A + P FET ?R TH(JA)
The R TH(JA) to be used in this equation normally includes
the R TH(JC) for the device plus the thermal resistance from
the board to the ambient temperature in the enclosure.
This value of T J can then be used to check the original
assumption for the junction temperature in the iterative
calculation process.
R DS(ON)
in discrete values.
V SENSE(MAX)
I O(MAX)
?
1 +
1
2
?
T
?
1
V O + V D
V IN(MIN)
+ 1
SEPIC Converter: Output Diode Selection
To maximize ef?ciency, a fast-switching diode with low
forward drop and low reverse leakage is desired. The output
diode in a SEPIC converter conducts current during the
switch off-time. The peak reverse voltage that the diode
V O + V D
I D(PEAK) = 1 + ?I O(MAX) ? + 1
Calculating Power MOSFET Switching and Conduction
Losses and Junction Temperatures
In order to calculate the junction temperature of the
power MOSFET, the power dissipated by the device must
be known. This power dissipation is a function of the
duty cycle, the load current and the junction temperature
itself. As a result, some iterative calculation is normally
required to determine a reasonably accurate value. Since
the controller is using the MOSFET as both a switching
and a sensing element, care should be taken to ensure
that the converter is capable of delivering the required
load current over all operating conditions (load, line and
temperature) and for the worst-case speci?cations for
V SENSE(MAX) and the R DS(ON) of the MOSFET listed in the
manufacturer’s data sheet.
must withstand is equal to V IN(MAX) + V O . The average
forward current in normal operation is equal to the output
current, and the peak current is equal to:
2 V IN(MIN)
The power dissipated by the diode is:
P D = I O(MAX) ? V D
and the diode junction temperature is:
T J = T A + P D ? R TH(JA)
The R TH(JA) to be used in this equation normally includes
the R TH(JC) for the device plus the thermal resistance from
the board to the ambient temperature in the enclosure.
1871fe
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC1871EMS#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:- 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
| LTC1871EMS#TR | 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) |
| LTC1871EMS#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) |
| LTC1871EMS-1#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) |
| LTC1871EMS-1#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) |
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