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| 型号： | MAX639CPA |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 10/13页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 5V/ADJ 225MA 8DIP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 50 |
| 类型： | 降压（降压） |
| 输出类型： | 两者兼有 |
| 输出数： | 1 |
| 输出电压： | 5V，1.3 V ~ 11.5 V |
| 输入电压： | 4 V ~ 11.5 V |
| 电流 - 输出： | 225mA |
| 同步整流器： | 无 |
| 工作温度： | 0°C ~ 70°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 |
| 其它名称： | Q724982 |
5V/3.3V/3V/Adjustable, High-Efficiency,
Low I Q , Step-Down DC-DC Converters
INPUT
+4.0V TO +11.5V
6
V+
LX
5
L = 100 μ H
OUTPUT
C IN
100 μ F
8
SHDN
MAX639 VOUT
MAX640
1
1N5817
R3
C OUT
100 μ F
MAX639
MAX640
MAX653
MAX653
VFB 7
GND
4
LBI
3
R4
Figure 4. Adjustable-Output Operation
Step 3: L = 50 / I PEAK . L will be in μH. Do not use an
inductor of less than 100μH.
Step 4: Make sure that I PEAK does not exceed 0.6A or
the inductor ’s maximum current rating,
whichever is lower.
Inductor series resistance affects both efficiency and
dropout voltage. A high series resistance severely limits
the maximum current available at lower input voltages.
Output currents up to 225mA are possible if the induc-
tor has low series resistance. Inductor and series
switch resistance form an LR circuit during t ON . If the
L/R time constant is less than the oscillator t ON , the
inductor’s peak current will fall short of the desired
I PEAK .
To maximize efficiency, choose the highest-value
inductor that will provide the required output current
over the whole range of your input voltage (see Typical
Operating Characteristics ). Inductors with peak cur-
rents in the 600mA range do not need to be very large.
They are about the size of a 1W resistor, with surface-
mount versions less than 5mm in diameter. Table 1 lists
suppliers of inductors suitable for use with the
MAX639/MAX640/MAX653.
Output Filter Capacitor
The MAX639/MAX640/MAX653’s output ripple has two
components. One component results from the variation
in stored charge on the filter capacitor with each LX
pulse. The other is the product of the current into the
capacitor and the capacitor’s equivalent series resis-
tance (ESR).
The amount of charge delivered in each oscillator pulse
is determined by the inductor value and input voltage.
Figure 5. Through-Hole PC Layout and Component Placement
Diagram for Standard Step-Down Application (Top-Side View)
It decreases with larger inductance, but increases as
the input voltage lessens. As a general rule, a smaller
amount of charge delivered in each pulse results in
less output ripple.
With low-cost aluminum electrolytic capacitors, the
ESR-induced ripple can be larger than that caused by
the charge variation. Consequently, high-quality alu-
minum-electrolytic or tantalum filter capacitors will mini-
mize output ripple. Best results at reasonable cost are
typically achieved with an aluminum-electrolytic capac-
itor in the 100μF range, in parallel with a 0.1μF ceramic
capacitor (Table 1).
External Diode
In most MAX639/MAX640/MAX653 circuits, the current
in the external diode (D1, Figure 3) changes abruptly
from zero to its peak value each time LX switches off.
To avoid excessive losses, the diode must have a fast
turn-on time. For low-power circuits with peak currents
less than 100mA, signal diodes such as the 1N4148
perform well. The 1N5817 diode works well for high-
power circuits, or for maximum efficiency at low power.
1N5817 equivalent diodes are also available in surface-
mount packages (Table 1). Although the 1N4001 and
other general-purpose rectifiers are rated for high cur-
rents, they are unacceptable because their slow turn-
off times result in excessive losses.
Minimum Load
Under no-load conditions, because of leakage from the
PMOS power switch (see the LX Leakage Current vs.
Temperature graph in the Typical Operating
Characteristics ) and from the internal resistor from V+
to V OUT , leakage current may be supplied to the output
10
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相关代理商/技术参数 |
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| MAX639CPA+ | 功能描述:直流/直流开关转换器 5/3.3/3V Adjustable Step-Down 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 |
| MAX639CSA | 功能描述:直流/直流开关转换器 5/3.3/3V Adjustable Step-Down 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 |
| MAX639CSA+ | 功能描述:直流/直流开关转换器 5/3.3/3V Adjustable Step-Down 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 |
| MAX639CSA+T | 功能描述:直流/直流开关转换器 5/3.3/3V Adjustable Step-Down 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 |
| MAX639CSA-T | 功能描述:直流/直流开关转换器 5/3.3/3V Adjustable Step-Down 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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