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参数资料
| 型号： | MIC2172BM TR |
| 厂商： | Micrel Inc |
| 文件页数： | 15/20页 |
| 文件大小： | 0K |
| 描述： | IC REG MULTI CONFIG 1.25A 8SOIC |
| 标准包装： | 2,500 |
| 类型： | 降压（降压），升压（升压），反相，Cuk |
| 输出数： | 1 |
| 输入电压： | 3 V ~ 40 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 100kHz |
| 电流 - 输出： | 1.25A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 8-SOIC |
| 其它名称： | MIC2172BMTR |
Micrel
MIC2172/3172
L1 ≤
( 4.75 × 0.623 ) 2
2 × 1.68 × 1 × 10 5
inverting input is also possible.
Voltage Clipper
I L1 ≤ 26.062μH (use 27μH)
Care must be taken to minimize T1’s leakage
I L1(peak) =
Equation (3) solves for L1’s maximum current value.
V IN T ON
L1
(3)
inductance, otherwise it may be necessary to
incorporate the voltage clipper consisting of D1, R4, and
C3 to avoid second breakdown (failure) of the
MIC3172’s power NPN Q1.
T ON = δ / f SW = 6.23×10 sec
4.75 × 6.23 × 10 ? 6
27 × 10 ? 6
Where:
-6
I L1(peak) =
I L1(peak) = 1.096A
Use a 27μH inductor with a peak current rating of at
Enable/Shutdown
The MIC3172 includes the enable/shutdown feature.
When the device is shutdown, total supply current is less
than 1μA. This is ideal for battery applications where
portions of a system are powered only when needed. If
this feature is not required, simply connect EN to V IN or
to a TTL high voltage.
least 1.4A.
Discontinuous Mode Design
Flyback Conversion
Flyback converter topology may be used in low power
applications where voltage isolation is required or
whenever the input voltage can be less than or greater
than the output voltage. As with the step-up converter
the inductor (transformer primary) current can be
continuous or discontinuous. Discontinuous operation is
When designing a discontinuous flyback converter, first
determine whether the device can safely handle the
peak primary current demand placed on it by the output
power. Equation (8) finds the maximum duty cycle
required for a given input voltage and output power. If
the duty cycle is greater than 0.8, discontinuous
operation cannot be used.
recommended.
Figure 12 shows a practical flyback converter design
using the MIC3172.
δ ≥
2 P OUT
I CL V IN(min)
(8)
Switch Operation
During Q1’s on time (Q1 is the internal NPN transistor—
see block diagrams), energy is stored in T1’s primary
inductance. During Q1’s off time, stored energy is
partially discharged into C4 (output filter capacitor).
For a practical example let:
P OUT = 5.0V × 0.25A = 1.25W
V IN = 4.0V to 6.0V
I CL = 1.25A when δ < 50%
Careful selection of a low ESR capacitor for C4 may
provide satisfactory output ripple voltage making
additional filter stages unnecessary.
C1 (input capacitor) may be reduced or eliminated if the
Then:
δ ≥
2 × 1.25
1.25 × 4
MIC3172 is located near a low impedance voltage
source.
Output Diode
The output diode allows T1 to store energy in its primary
inductance (D2 nonconducting) and release energy into
C4 (D2 conducting). The low forward voltage drop of a
Schottky diode minimizes power loss in D2.
δ ≥ 0.5 (50%) Use 0.55.
The slightly higher duty cycle value is used to overcome
circuit inefficiencies. A few iterations of equation (8) may
be required if the duty cycle is found to be greater than
50%.
Calculate the maximum transformer turns ratio a, or
N PRI /N SEC , that will guarantee safe operation of the
MIC2172/3172 power switch.
Frequency Compensation
A simple frequency compensation network consisting of
R3 and C2 prevents output oscillations.
High impedance output stages (transconductance type)
a ≤
Where:
V CE F CE ± V IN(max)
V SEC
(9)
in the MIC2172/3172 often permit simplified loop-stability
solutions to be connected to circuit ground, although a
more conventional technique of connecting the
components from the error amplifier output to its
a = transformer maximum turns ratio
V CE = power switch collector to emitter maximum
voltage
April 2006
15
M9999-041806
(408) 955-1690
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| MIC2172BN | 功能描述:IC REG BUCK BOOST INV CUK 8DIP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:20 系列:SIMPLE SWITCHER® 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 V ~ 60 V PWM 型:电压模式 频率 - 开关:52kHz 电流 - 输出:1A 同步整流器:无 工作温度:-40°C ~ 125°C 安装类型:通孔 封装/外壳:16-DIP（0.300"，7.62mm） 包装:管件 供应商设备封装:16-DIP 其它名称:*LM2575HVN-12LM2575HVN-12 |
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| MIC2172YM TR | 功能描述:直流/直流开关调节器 1.25A 100kHz Switching Regulator (Lead Free) 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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| MIC2172YM-TR | 制造商:Micrel Inc 功能描述: |
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