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参数资料
| 型号： | L7981ATR |
| 厂商： | STMICROELECTRONICS |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, DSO8 |
| 封装： | 3 X 3 MM, 1.08 MM HEIGHT, ROHS COMPLIANT, HSOP-8 |
| 文件页数： | 7/44页 |
| 文件大小： | 1315K |
| 代理商： | L7981ATR |
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L7981
Application informations
Doc ID 15182 Rev 3
15/44
6
Application informations
6.1
Input capacitor selection
The capacitor connected to the input has to be capable to support the maximum input
operating voltage and the maximum RMS input current required by the device. The input
capacitor is subject to a pulsed current, the RMS value of which is dissipated over its ESR,
affecting the overall system efficiency.
So the input capacitor must have a RMS current rating higher than the maximum RMS input
current and an ESR value compliant with the expected efficiency.
The maximum RMS input current flowing through the capacitor can be calculated as:
Equation 3
Where Io is the maximum DC output current, D is the duty cycle,
η is the efficiency.
Considering
η=1, this function has a maximum at D=0.5 and it is equal to Io/2.
In a specific application the range of possible duty cycles has to be considered in order to
find out the maximum RMS input current. The maximum and minimum duty cycles can be
calculated as:
Equation 4
and
Equation 5
Where VF is the forward voltage on the freewheeling diode and VSW is voltage drop across
the internal PDMOS.
The peak to peak voltage across the input capacitor can be calculated as:
Equation 6
where ESR is the equivalent series resistance of the capacitor.
I
RMS
I
O
D
2D
2
η
---------------
–
D
2
η
2
-------
+
=
D
MAX
V
OUT
V
F
+
V
INMIN
V
SW
–
-------------------------------------
=
D
MIN
V
OUT
V
F
+
V
INMAX
V
SW
–
--------------------------------------
=
V
PP
I
O
C
IN
F
SW
-------------------------
1
D
η
----
–
D
η
----
1D
–
()
+
ESR I
O
+
=
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相关代理商/技术参数 |
参数描述 |
|---|---|
| L7981ATR/BLK | 制造商:STMicroelectronics 功能描述:3 A STEP-DOWN SWITCHING REGULATO - Tape and Reel 制造商:STMicroelectronics 功能描述:STMicroelectronics L7981ATR/BLK Interface Misc |
| L7981TR | 功能描述:直流/直流开关调节器 3A DC 4.5 V to 28 V Adj 0.6V 250 kHz RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| L7983 | 制造商:Leviton Manufacturing Co 功能描述: |
| L7985 | 功能描述:线性稳压器 - 标准 2A Step Down REG 4.5V to 38V 250 KHz RoHS:否 制造商:STMicroelectronics 输出类型: 极性: 输出电压:1.8 V 输出电流:150 mA 负载调节: 最大输入电压:5.5 V 线路调整率: 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:SOT-323-5L |
| L7985A | 功能描述:直流/直流开关调节器 2A DC 4.5V to 38V 250 KHz Step-Down RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
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