参数资料
| 型号： | MIC4721YMMTR |
| 厂商： | Micrel Inc |
| 文件页数： | 9/19页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 1.5A 10MSOP |
| 标准包装： | 2,500 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 可调至 1V |
| 输入电压： | 2.7 V ~ 5.5 V |
| 频率 - 开关： | 2MHz |
| 电流 - 输出： | 1.5A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 10-MSOP |
| 其它名称： | MIC4721YMM TR |
Micrel, Inc.
MIC4721
Application Information
The MIC4721 is a 1.5A PWM non-synchronous buck
regulator. A regulated DC output voltage is obtained by
switching an input voltage supply, and filtering the
switched voltage through an inductor and capacitor.
Figure 1 shows a simplified example of a non-synch-
ronous buck converter and its input/output voltage.
Figure 2. Continuous Operation
The output voltage is regulated by pulse width
modulating (PWM) the switch voltage to the average
required output voltage. The switching can be broken up
into two cycles; On and Off.
As seen in Figure 3, the high side switch is turned on
(on-time) and current flows from the input supply through
the inductor and to the output.
Figure 1. Simplified Buck Converter
For a non-synchronous buck converter, there are two
modes of operation; continuous and discontinuous. The
mode refers to the state of current in the inductor. If
current continuously flows through the inductor
throughout the switching cycle, it is in continuous
operation. If the inductor current drops to zero during the
off time, it is in discontinuous operation. Critically
continuous is the point where any decrease in output
current will cause it to enter discontinuous operation.
The critically continuous load current can be calculated
as follows.
V OUT ?
I OUT _ CRITICAL =
V OUT
V IN
2 × L × f S
2
Where: f S is the switching frequency (2MHz for the
MIC4721).
L is the output inductance (Henry).
When I OUT is less than I OUT_CRITICAL , the buck converter
operates in discontinuous mode and the inductor current
goes to zero before the end of each switching cycle.
Figure 3. On-Time
The inductor current is charged at the rate:
When I OUT is greater than I OUT_CRITICAL , the converter
operates in continuous mode and current always flows in
( V IN
? V OUT )
the inductor. Continuous or discontinuous operation
determines how peak inductor current is calculated.
Continuous Operation
L
To determine the total on-time, or time at which the
inductor charges, the duty cycle needs to be calculated.
The duty cycle can be calculated as:
Figure 2 illustrates the switch voltage and inductor
current during continuous operation.
D =
V OUT
V IN
and the On time is:
May 2007
9
M9999-052907-A
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