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參數(shù)資料
| 型號： | L7980A |
| 廠商： | STMICROELECTRONICS |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 3.5 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | ROHS COMPLIANT, HSOP-8 |
| 文件頁數(shù)： | 3/44頁 |
| 文件大?。?/td> | 1247K |
| 代理商： | L7980A |
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L7980
Functional description
Doc ID 15181 Rev 3
11/44
5.2
Soft-start
The soft-start is essential to assure correct and safe start up of the step-down converter. It
avoids inrush current surge and makes the output voltage increases monothonically.
The soft -start is performed by a staircase ramp on the non-inverting input (VREF) of the
error amplifier. So the output voltage slew rate is:
Equation 1
where SRVREF is the slew rate of the non-inverting input, while R1and R2 is the resistor
divider to regulate the output voltage (see Figure 7). The soft-start stair case consists of 64
steps of 9.5 mV each one, from 0 V to 0.6 V. The time base of one step is of 32 clock cycles.
So the soft start time and then the output voltage slew rate depend on the switching
frequency.
Figure 7.
Soft start scheme
Soft start time results:
Equation 2
For example with a switching frequency of 250 kHz the SSTIME is 8 ms.
5.3
Error amplifier and compensation
The error amplifier (E/A) provides the error signal to be compared with the sawtooth to
perform the pulse width modulation. Its non-inverting input is internally connected to a 0.6 V
voltage reference, while its inverting input (FB) and output (COMP) are externally available
for feedback and frequency compensation. In this device the error amplifier is a voltage
mode operational amplifier so with high DC gain and low output impedance.
The uncompensated error amplifier characteristics are the following:
SR
OUT
SR
VREF
1
R1
R2
--------
+
=
SS
TIME
32 64
Fsw
-----------------
=
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| L7980ATR | 功能描述:直流/直流開關轉換器 2 A Step-Down Reg 4.5V to 28V 250 kHz RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| L7980TR | 功能描述:直流/直流開關轉換器 2A DC 4.5 V to 28 V Adj 0.6V 250 kHz RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| L7981 | 功能描述:直流/直流開關調(diào)節(jié)器 3A Step-Down Reg 3A DC 4.5-28V 250Khz 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 |
| L7981A | 制造商:STMicroelectronics 功能描述:POWER CONVERSION - Rail/Tube 制造商:STMicroelectronics 功能描述:3A Step-Down Reg 3.7A 4.5 to 28V 1MHz 制造商:ST 功能描述:3A STEP-DOWN SWITCHING REGULATOR |
| L7981ATR | 功能描述:直流/直流開關調(diào)節(jié)器 3 A Step-Down Reg 4.5V to 28V 250 kHz 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 |
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