ZHCSHW2I June 2007 – September 2018 LM2735
PRODUCTION DATA.
- 1 特性
- 2 應用
- 3 說明
- 4 修訂歷史記錄
- 5 Pin Configuration and Functions
- 6 Specifications
- 7 Detailed Description
-
8 Application and Implementation
- 8.1 Application Information
- 8.2
Typical Applications
- 8.2.1 LM2735X SOT-23 Design Example 1
- 8.2.2 LM2735Y SOT-23 Design Example 2
- 8.2.3 LM2735X WSON Design Example 3
- 8.2.4 LM2735Y WSON Design Example 4
- 8.2.5 LM2735Y MSOP-PowerPAD Design Example 5
- 8.2.6 LM2735X SOT-23 Design Example 6
- 8.2.7 LM2735Y SOT-23 Design Example 7
- 8.2.8 LM2735X SOT-23 Design Example 8
- 8.2.9 LM2735Y SOT-23 Design Example 9
- 8.2.10 LM2735X WSON Design Example 10
- 8.2.11 LM2735Y WSON Design Example 11
- 8.2.12 LM2735X WSON SEPIC Design Example 12
- 8.2.13 LM2735Y MSOP-PowerPAD SEPIC Design Example 13
- 8.2.14 LM2735X SOT-23 LED Design Example 14
- 8.2.15 LM2735Y WSON FlyBack Design Example 15
- 8.2.16 LM2735X SOT-23 LED Design Example 16 VRAIL > 5.5 V Application
- 8.2.17 LM2735X SOT-23 LED Design Example 17 Two-Input Voltage Rail Application
- 8.2.18 SEPIC Converter
- 9 Power Supply Recommendations
- 10Layout
- 11器件和文檔支持
- 12機械、封裝和可訂購信息
封裝選項
機械數據 (封裝 | 引腳)
散熱焊盤機械數據 (封裝 | 引腳)
- DGN|8
訂購信息
8.2.1.2.2 Inductor Selection
The duty cycle (D) can be approximated quickly using the ratio of output voltage (VO) to input voltage (VIN):
Therefore:
Power losses due to the diode (D1) forward voltage drop, the voltage drop across the internal NMOS switch, the voltage drop across the inductor resistance (RDCR), and switching losses must be included to calculate a more accurate duty cycle (see Calculating Efficiency, and Junction Temperature for a detailed explanation). A more accurate formula for calculating the conversion ratio is:
where
- η equals the efficiency of the LM2735 application.
The inductor value determines the input ripple current. Lower inductor values decrease the size of the inductor, but increase the input ripple current. An increase in the inductor value will decrease the input ripple current.
Figure 19. Inductor Current 
A good design practice is to design the inductor to produce 10% to 30% ripple of maximum load. From the previous equations, the inductor value is then obtained.
where
- 1/TS = FSW = switching frequency
Ensure that the minimum current limit (2.1 A) is not exceeded, so the peak current in the inductor must be calculated. The peak current (ILPK ) in the inductor is calculated by:
or
When selecting an inductor, make sure that it is capable of supporting the peak input current without saturating. Inductor saturation will result in a sudden reduction in inductance and prevent the regulator from operating correctly. Because of the speed of the internal current limit, the peak current of the inductor need only be specified for the required maximum input current. For example, if the designed maximum input current is 1.5 A and the peak current is 1.75 A, then the inductor should be specified with a saturation current limit of >1.75 A. There is no need to specify the saturation or peak current of the inductor at the 3-A typical switch current-limit.
Because of the operating frequency of the LM2735, ferrite based inductors are preferred to minimize core losses. This presents little restriction since the variety of ferrite-based inductors is huge. Lastly, inductors with lower series resistance (DCR) will provide better operating efficiency. For recommended inductors, see the following design examples.