ZHCSF76B July   2016  – December 2019 TPS22918-Q1

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
  3. 3 说明
    1.     Device Images
      1.      简化原理图
      2.      导通电阻与输入电压间的关系典型值
  4. 4 修订历史记录
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics
    7. 6.7 Typical DC Characteristics
    8. 6.8 Typical AC Characteristics
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 On and Off Control
      2. 8.3.2 Quick Output Discharge (QOD)
        1. 8.3.2.1 QOD when System Power is Removed
        2. 8.3.2.2 Internal QOD Considerations
      3. 8.3.3 Adjustable Rise Time (CT)
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Input Capacitor (CIN)
        2. 9.2.2.2 Output Capacitor (CL) (Optional)
        3. 9.2.2.3 Shutdown Sequencing During Unexpected System Power Loss
        4. 9.2.2.4 VIN to VOUT Voltage Drop
        5. 9.2.2.5 Inrush Current
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
    3. 11.3 Thermal Considerations
  12. 12器件和文档支持
    1. 12.1 器件支持
      1. 12.1.1 开发支持
    2. 12.2 文档支持
      1. 12.2.1 相关文档
    3. 12.3 接收文档更新通知
    4. 12.4 社区资源
    5. 12.5 商标
    6. 12.6 静电放电警告
    7. 12.7 Glossary
  13. 13机械、封装和可订购信息

8.3.3 Adjustable Rise Time (CT)

A capacitor to GND on the CT pin sets the slew rate for each channel. The capacitor to GND on the CT pin must be rated for 25 V and above. An approximate formula for the relationship between CT and slew rate is shown in Equation 3.

Equation 3. SR = 0.55 × CT + 30

where

  • SR is the slew rate (in µs/V)
  • CT is the capacitance value on the CT pin (in pF)
  • The units for the constant 30 are µs/V. The units for the constant 0.55 are µs/(V × pF)

Equation 3 accounts for 10% to 90% measurement on VOUT and does not apply for CT less than 100 pF. Use Table 2 to determine rise times for when CT is greater or equal to 100 pF.

Rise time can be calculated by multiplying the input voltage by the slew rate. Table 2 contains rise time values measured on a typical device.

Table 2. Rise Time Table

CTx (pF) RISE TIME (µs) 10% - 90%, CL = 0.1 µF, CIN = 1 µF, RL = 10 Ω
Typical values at 25°C with a 25-V X7R 10% ceramic capacitor on CT
VIN = 5 V VIN = 3.3 V VIN = 2.5 V VIN = 1.8 V VIN = 1.5 V VIN = 1.2V VIN = 1.0 V
0 135 95 75 60 50 45 40
220 650 455 350 260 220 185 160
470 1260 850 655 480 415 340 300
1000 2540 1680 1300 960 810 660 560
2200 5435 3580 2760 2020 1715 1390 1220
4700 12050 7980 6135 4485 3790 3120 2735
10000 26550 17505 13460 9790 8320 6815 5950

As the voltage across the capacitor approaches the capacitor rated voltage, the effective capacitance reduces. Depending on the dielectric material used, the voltage coefficient changes. See Table 3 for the recommended minimum voltage rating for the CT capacitor.

Table 3. Recommended CT Capacitor Voltage Rating

VIN (V) RECOMMENDED CT CAPACITOR VOLTAGE RATING (V)(1)
1 V to 1.2 V 10
1.2 V to 4 V 16
4 V to 5.5 V 20
(1) If using VIN = 1.2 V or 4 V, it is recommended to use the higher voltage rating.
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