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| 型号： | LM2574N-012 |
| 厂商： | ON Semiconductor |
| 文件页数： | 19/26页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 12V 0.5A 8DIP |
| 产品变化通告： | Product Discontinuation 27/Jun/2007 |
| 标准包装： | 50 |
| 类型： | 降压（降压） |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 12V |
| 输入电压： | 4.75 V ~ 40 V |
| PWM 型： | 电压模式 |
| 频率 - 开关： | 52kHz |
| 电流 - 输出： | 500mA |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 通孔 |
| 封装/外壳： | 8-DIP（0.300"，7.62mm） |
| 包装： | 管件 |
| 供应商设备封装： | 8-PDIP |
LM2574, NCV2574
The high input current needed for startup is now partially
supplied by the input capacitor C in .
Design Recommendations:
The inverting regulator operates in a different manner
than the buck converter and so a different design procedure
has to be used to select the inductor L1 or the output
capacitor C out .
by the fact, that the ground pin of the converter IC is no
longer at ground. Now, the ON/OFF pin threshold voltage
(1.3 V approximately) has to be related to the negative
output voltage level. There are many different possible
shutdown methods, two of them are shown in Figures 29
and 30.
The output capacitor values must be larger than what is
normally required for buck converter designs. Low input
+V in
+V in
LM2574?XX
voltages or high output currents require a large value output
5 (12)
capacitor (in the range of thousands of m F).
The recommended range of inductor values for the
inverting converter design is between 68 m H and 220 m H. To
select an inductor with an appropriate current rating, the
inductor peak current has to be calculated.
5.0 V
0
On
Off
Shutdown
Input
R3
470
C in
22 m F
R1
47 k
3
ON/OFF 2
(5) and
4
R2
Gnds
Pins
(4)
and
(6)
22 m F
+V in
5 (12)
1
68 m H
12 to 25 V
Unregulated
DC Input
C in
C1
/50 V 0.1 m F
3 ON/OFF 4 Pwr 2
LM2574?12
(3)
(14)
Feedback
Output
7
Sig
L1
47 k
MOC8101
NOTE : This picture does not show the complete circuit.
?V out
R1
47 k
(5)
R2
Gnd
(6)
Gnd
(4)
D1
MBR150
C out
680 m F
/16 V
Figure 29. Inverting Buck?Boost Regulator Shutdown
Circuit Using an Optocoupler
47 k
?12 V @ 100 mA
Regulated
Output
Figure 28. Inverting Buck?Boost Regulator with
+V
0
On
Off
R2
Shutdown
Input
Delayed Startup
+V in
5.6 k
+V in
I V ) |V | V
) in
[
peak
2L 1
in
The following formula is used to obtain the peak inductor
current:
Load in O x t on
I
V
C in
22 m F
5
Q1
2N3906
(12)
LM2574?XX
3 ON/OFF 2
(5) and
Gnds (4)
Pins and
O
) |V |
where
t on +
V
|V |
in O
x 1.0
f osc
, and f osc = 52 kHz.
R1
12 k
4
?V out
(6)
Under normal continuous inductor current operating
conditions, the worst case occurs when V in is minimal.
It has been already mentioned above, that in some
situations, the delayed startup or the undervoltage lockout
features could be very useful. A delayed startup circuit
applied to a buck?boost converter is shown in Figure 28.
Figure 34 in the “Undervoltage Lockout” section describes
an undervoltage lockout feature for the same converter
topology.
With the inverting configuration, the use of the ON/OFF
NOTE : This picture does not show the complete circuit.
Figure 30. Inverting Buck?Boost Regulator Shutdown
Circuit Using a PNP Transistor
Negative Boost Regulator
This example is a variation of the buck?boost topology
and it is called negative boost regulator. This regulator
experiences relatively high switch current, especially at low
input voltages. The internal switch current limiting results in
lower output load current capability.
pin requires some level shifting techniques. This is caused
http://onsemi.com
19
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM2574N-012G | 功能描述:直流/直流开关转换器 12V 500mA Buck PWM 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 |
| LM2574N-015 | 功能描述:直流/直流开关调节器 15V 500mA Buck PWM 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 |
| LM2574N-015G | 功能描述:直流/直流开关调节器 15V 500mA Buck PWM 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 |
| LM2574N-12 | 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 |
| LM2574N-12 NOPB | 制造商:National Semiconductor 功能描述:Conv DC-DC Single Step Down 4V to 40V 8-Pin PDIP Rail |
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