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参数资料
| 型号： | LM2597-12MWC |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 1.4 A SWITCHING REGULATOR, 173 kHz SWITCHING FREQ-MAX, UUC |
| 封装： | WAFER |
| 文件页数： | 21/40页 |
| 文件大小： | 1019K |
| 代理商： | LM2597-12MWC |
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Application Information (Continued)
To use the bias supply feature with output voltages between
4V and 15V, wire the bias pin to the regulated output. Since
the V
BS pin requires a minimum of 4V to operate, the 3.3V
part cannot be used this way. When the V
BS pin is left open,
the intemal regulator circuitry is powered from the input
voltage.
SHUTDOWN /SOFT-START
The circuit shown in
Figure 28 is a standard buck regulator
with 24V in, 12V out, 100 mA load, and using a 0.068 F
Soft-start capacitor. The photo in
Figure 26 and Figure 27
show the effects of Soft-start on the output voltage, the input
current, with, and without a Soft-start capacitor.
Figure 26
also shows the error flag output going high when the output
voltage reaches 95% of the nominal output voltage. The
reduced input current required at startup is very evident
when comparing the two photos. The Soft-start feature re-
duces the startup current from 700 mA down to 160 mA, and
delays and slows down the output voltage rise time.
This reduction in start up current is useful in situations where
the input power source is limited in the amount of current it
can deliver. In some applications Soft-start can be used to
replace undervoltage lockout or delayed startup functions.
If a very slow output voltage ramp is desired, the Soft-start
capacitor can be made much larger. Many seconds or even
minutes are possible.
If only the shutdown feature is needed, the Soft-start capaci-
tor can be eliminated.
DS012440-43
FIGURE 24. Effects of Bias Supply Feature on 5V
Regulator Efficiency
DS012440-45
FIGURE 25. Effects of Bias Supply Feature on 12V
Regulator Efficiency
DS012440-44
FIGURE 26. Output Voltage, Input Current, Error Flag
Signal, at Start-Up, WITH Soft-start
DS012440-46
FIGURE 27. Output Voltage, Input Current, at Start-Up,
WITHOUT Soft-start
LM2597/LM2597HV
www.national.com
28
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| LM2597HVM-3.3/NOPB | 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
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