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参数资料
| 型号： | L4972AD |
| 厂商： | STMICROELECTRONICS |
| 元件分类： | 稳压器 |
| 英文描述： | 3.5 A SWITCHING REGULATOR, 200 kHz SWITCHING FREQ-MAX, PDSO20 |
| 封装： | PLASTIC, SO-20 |
| 文件页数： | 17/22页 |
| 文件大小： | 1370K |
| 代理商： | L4972AD |
L4972A
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stage. An error signal is produced by comparing the output voltage with the precise 5.1V ± 2% on chip
reference. This error signal is then compared with the sawtooth oscillator in order to generate frixed fre-
quency pulse width modulated drive for the output stage. A PWM latch is included to eliminate multiple
pulsing within a period even in noisy environments.
The gain and stability of the loop can be adjusted by an external RC network connected to the output of
the error amplifier. A voltage feedforward control has been added to the oscillator, this maintains superior
line regulation over a wide input voltage range. Closing the loop directly gives an output vol-tage of 5.1V,
higher voltages are obtained by inserting a voltage divider.
At turn on, output overcurrents are prevented by the soft start function (fig. 5). The error amplifier is initially
clamped by an external capacitor, Css, and allowed to rise linearly under the charge of an internal constant
current source.
Output overload protection is provided by a current limit circuit. The load current is sensed by a internal
metal resistor connected to a comparator. When the load current exceeds a preset threshold, the output
of the comparator sets a flip flop which turns off the power DMOS. The next clock pulse, from an internal
40kHz oscillator, will reset the flip flop and the power DMOS will again conduct. This current protection
method, ensures a constant current output when the system is overloaded or short circuited and limits the
switching frequency, in this condition, to 40kHz. The Reset and Power fail diagram (fig. 7), generates an
output signal when the supply voltage exceeds a threshold programmed by an external voltage divider.
The reset signal, is generated with a delay time programmed by a external capacitor on the delay pin.
When the supply voltage falls below the threshold or the output voltage goes below 5V, the reset output
goes low immediately. The reset output is an open drain.
Fig. 7A shows the case when the supply voltage is higher than the threshold, but the output voltage is not
yet 5V.
Fig. 7B shows the case when the output is 5.1V, but the supply voltage is not yet higher than the fixed
threshold. The thermal protection disables circuit operation when the junction temperature reaches about
150°C and has a hysterysis to prevent unstable conditions.
Figure 4. Feedforward Waveform.
Figure 5. Soft Start Function.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| L4972AD013TR | 功能描述:直流/直流开关调节器 5.1 to 40V 2.0 Amp 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 |
| L4972D | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Voltage-Mode SMPS Controller |
| L4973 | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:3.5A step down switching regulator |
| L4973D3 | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:3.5A STEP DOWN SWITCHING REGULATOR |
| L4973D3.3 | 功能描述:直流/直流开关调节器 3.3V 3.5A 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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