ZHCSGZ0B October 2017 – November 2017 TPS23525
PRODUCTION DATA.
- 1 特性
- 2 应用
- 3 说明
- 4 修订历史记录
- 5 Pin Configuration and Functions
- 6 Specifications
- 7 Parameter Measurement Information
- 8 Detailed Description
-
9 Application and Implementation
- 9.1 Application Information
- 9.2
Typical Application
- 9.2.1 Design Requirements
- 9.2.2
Detailed Design Procedure
- 9.2.2.1 Selecting RSNS
- 9.2.2.2 Selecting Soft Start Setting: CSS and CSS,VEE
- 9.2.2.3 Selecting VDS Switch Over Threshold
- 9.2.2.4 Timer Selection
- 9.2.2.5 MOSFET Selection and SOA Checks
- 9.2.2.6 Input Cap, Input TVS, and OR-ing FET selection
- 9.2.2.7 EMI Filter Consideration
- 9.2.2.8 Under Voltage and Over Voltage Settings
- 9.2.2.9 Choosing RVCC and CVCC
- 9.2.2.10 Power Good Interface to Downstream DC/DC
- 9.2.3 Application Curves
- 10Power Supply Recommendations
- 11Layout
- 12器件和文档支持
- 13机械、封装和可订购信息
9.2.2.2 Selecting Soft Start Setting: CSS and CSS,VEE
First, compute the minimum inrush current where the timer will trip using equation below.
To avoid running the timer the inrush current needs to be sufficiently low. Target 0.4 A of inrush current to allow margin, and compute the target CSS using equation below.
Next choose, the next available CSS greater than 39.6 nF. For this example 43 nF was used, which assumes a 33 nF and 10 nF cap in parallel. This results in an inrush current of 0.37 A at max COUT (792 µF) and inrush current of 0.31 A at typical COUT (660 µF). Also it is recommended to add a capacitor between the soft start pin and VEE (CSS,VEE) to improve immunity to input voltage noise during soft start. It's recommended to chose a capacitor that's 3x larger than CSS. In this case a 150 nF capacitor was chosen.
Finally the start-up time at maximum input voltage can be computed using the equation below:
