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| 型号： | LM2574N-015 |
| 厂商： | ON Semiconductor |
| 文件页数： | 18/26页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 15V 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： | 15V |
| 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
4. R q JC
5. R q JA
t
d + on + O ,
in
Since the current rating of the LM2574 is only 0.5 A, the
total package power dissipation for this switcher is quite
low, ranging from approximately 0.1 W up to 0.75 W under
varying conditions. In a carefully engineered printed circuit
board, the through?hole DIP package can easily dissipate up
to 0.75 W, even at ambient temperatures of 60 ° C, and still
keep the maximum junction temperature below 125 ° C.
Thermal Analysis and Design
The following procedure must be performed to determine
the operating junction temperature. First determine:
1. P D(max) ? maximum regulator power dissipation in
the application.
2. T A(max) ? maximum ambient temperature in the
application.
3. T J(max) ? maximum allowed junction temperature
(125 ° C for the LM2574). For a conservative
design, the maximum junction temperature
should not exceed 110 ° C to assure safe
operation. For every additional +10 ° C
temperature rise that the junction must
withstand, the estimated operating lifetime
of the component is halved.
? package thermal resistance junction?case.
? package thermal resistance junction?ambient.
The following formula is to calculate the approximate
total power dissipated by the LM2574:
P D = (V in x I Q ) + d x I Load x V sat
where d is the duty cycle and for buck converter
V
T V
I Q (quiescent current) and V sat can be found in the
LM2574 data sheet,
V in is minimum input voltage applied,
V O is the regulator output voltage,
I Load is the load current.
T J = (R q JA )(P D ) + T A
where (R q JA )(P D ) represents the junction temperature rise
caused by the dissipated power and T A is the maximum
ambient temperature.
Some Aspects That can Influence Thermal Design
It should be noted that the package thermal resistance and
the junction temperature rise numbers are all approximate,
and there are many factors that will affect these numbers,
such as PC board size, shape, thickness, physical position,
location, board temperature, as well as whether the
surrounding air is moving or still. At higher power levels the
thermal resistance decreases due to the increased air current
activity.
Other factors are trace width, total printed circuit copper
area, copper thickness, single? or double?sided, multilayer
board, the amount of solder on the board or even color of the
traces.
The size, quantity and spacing of other components on the
board can also influence its effectiveness to dissipate the
heat. Some of them, like the catch diode or the inductor will
generate some additional heat.
ADDITIONAL APPLICATIONS
Inverting Regulator
An inverting buck?boost regulator using the LM2574?12
is shown in Figure 27. This circuit converts a positive input
voltage to a negative output voltage with a common ground
by bootstrapping the regulators ground to the negative
output voltage. By grounding the feedback pin, the regulator
senses the inverted output voltage and regulates it.
In this example the LM2574?12 is used to generate a ?12 V
output. The maximum input voltage in this case cannot
exceed 28 V because the maximum voltage appearing across
the regulator is the absolute sum of the input and output
voltages and this must be limited to a maximum of 40 V.
This circuit configuration is able to deliver approximately
0.1 A to the output when the input voltage is 8.0 V or higher.
At lighter loads the minimum input voltage required drops
to approximately 4.7 V, because the buck?boost regulator
L1
(5)
8.0 to 25 V
Unregulated
DC Input +V in
5
C in
22 m F
4
LM2574?12
(12)
Pwr 2 Sig 3
Gnd Gnd
(6) (4)
(3)
(14)
Feedback
1
68 m H
Output
7
ON/OFF D1
MBR150
C out
680 m F
topology can produce an output voltage that, in its absolute
value, is either greater or less than the input voltage.
Since the switch currents in this buck?boost configuration
are higher than in the standard buck converter topology, the
available output current is lower.
This type of buck?boost inverting regulator can also
require a larger amount of startup input current, even for
?12 V @ 100 mA
Regulated
Output
Figure 27. Inverting Buck?Boost Develops ?12 V
The dynamic switching losses during turn?on and
turn?off can be neglected if a proper type catch diode is used.
The junction temperature can be determined by the
light loads. This may overload an input power source with
a current limit less than 0.6 A.
Because of the relatively high startup currents required by
this inverting regulator topology, the use of a delayed startup
or an undervoltage lockout circuit is recommended.
While using a delayed startup arrangement, the input
capacitor can charge up to a higher voltage before the
switch?mode regulator begins to operate.
following expression:
http://onsemi.com
18
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相关代理商/技术参数 |
参数描述 |
|---|---|
| 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 |
| LM2574N12 | 制造商:Texas Instruments 功能描述:SWITCHING REG 0.5A 12V 2574 DIP8 |
| LM2574N-12/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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