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参数资料
| 型号： | MIC2172YN |
| 厂商： | Micrel Inc |
| 文件页数： | 14/20页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK BOOST INV CUK 8DIP |
| 标准包装： | 50 |
| 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： | 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 |
| 产品目录页面： | 1092 (CN2011-ZH PDF) |
| 其它名称： | 576-2151 MIC2172YN-ND |
Micrel
MIC2172/3172
L1 is operating in continuous mode if it does not
discharge completely before the MIC2172/3172 power
switch is turned on again.
Discontinuous Mode Design
Given the maximum output current, solve equation (1) to
determine whether the device can operate in
discontinuous mode without initiating the internal device
current limit.
? I CL ?
Figure 10. Single Point Ground
I OUT
≤
? ? V IN δ
? 2 ?
V OUT
(1)
A single point ground is strongly recommended for
proper operation.
The signal ground, compensation network ground, and
δ =
V OUT + V F ± V IN
V OUT + V F
(1a)
feedback network connections are sensitive to minor
voltage variations. The input and output capacitor
grounds and power ground conductors will exhibit
voltage drop when carrying large currents. Keep the
sensitive circuit ground traces separate from the power
ground traces. Small voltage variations applied to the
sensitive circuits can prevent the MIC2172/3172 or any
switching regulator from functioning properly.
Applications and Design Hints
Access to both the collector and emitter(s) of the NPN
power switch makes the MIC2172/3172 extremely
versatile and suitable for use in most PWM power supply
topologies.
Boost Conversion
Refer to figure 11 for a typical boost conversion
application where a +5V logic supply is available but
+12V at 0.14A is required.
Where:
I CL = internal switch current limit
I CL = 1.25A when δ < 50%
I CL = 0.833 (2 – δ ) when δ ≥ 50%
(Refer to Electrical Characteristics.)
I OUT = maximum output current
V IN = minimum input voltage
δ = duty cycle
V OUT = required output voltage
V F = D1 forward voltage drop
For the example in figure 11.
I OUT = 0.14A
I CL = 1.147A
V IN = 4.75V (minimum)
δ = 0.623
V OUT = 12.0V
V F = 0.6V
Then:
? × 4.75 × 0.623
?
≤ ?
I OUT
I OUT
? 1.147 ?
2 ?
≤ 0.141A
12
This value is greater than the 0.14A output current
requirement so we can proceed to find the inductance
Figure 11. 5V to 12V Boost Converter
value of L1.
The first step in designing a boost converter is
determining whether inductor L1 will cause the converter
to operate in either continuous or discontinuous mode.
L1 ≤
( V IN δ ) 2
2 P OUT f SW
(2)
f SW = 1 ? 10 kHz (100kHz)
Discontinuous mode is preferred because the feedback
control of the converter is simpler.
When L1 discharges its current completely during the
MIC2172/3172’s off-time, it is operating in discontinuous
mode.
Where:
P OUT = 12 ? 0.14 = 1.68W
5
For our practical example:
April 2006
14
M9999-041806
(408) 955-1690
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