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參數(shù)資料
| 型號： | L7981TR |
| 廠商： | STMICROELECTRONICS |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING REGULATOR, DSO8 |
| 封裝： | 3 X 3 MM, 1.08 MM HEIGHT, ROHS COMPLIANT, VFQFP-8 |
| 文件頁數(shù)： | 7/44頁 |
| 文件大?。?/td> | 1315K |
| 代理商： | L7981TR |
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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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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| L7983 | 制造商:Leviton Manufacturing Co 功能描述: |
| L7985 | 功能描述:線性穩(wěn)壓器 - 標準 2A Step Down REG 4.5V to 38V 250 KHz RoHS:否 制造商:STMicroelectronics 輸出類型: 極性: 輸出電壓:1.8 V 輸出電流:150 mA 負載調(diào)節(jié): 最大輸入電壓:5.5 V 線路調(diào)整率: 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:SOT-323-5L |
| L7985A | 功能描述:直流/直流開關調(diào)節(jié)器 2A DC 4.5V to 38V 250 KHz Step-Down RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
| L7985ATR | 功能描述:線性穩(wěn)壓器 - 標準 2A Step-Down REG 2A DC 4.5 to 38V RoHS:否 制造商:STMicroelectronics 輸出類型: 極性: 輸出電壓:1.8 V 輸出電流:150 mA 負載調(diào)節(jié): 最大輸入電壓:5.5 V 線路調(diào)整率: 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:SOT-323-5L |
| L7985TR | 功能描述:線性穩(wěn)壓器 - 標準 2A Step-Down Reg 4.5V to 38V 250 KHz RoHS:否 制造商:STMicroelectronics 輸出類型: 極性: 輸出電壓:1.8 V 輸出電流:150 mA 負載調(diào)節(jié): 最大輸入電壓:5.5 V 線路調(diào)整率: 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:SOT-323-5L |
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