ZHCSKC4H May   2008  – October 2021

PRODMIX  

  1. 特性
  2. 应用
  3. 描述
  4. Revision History
  5. Pin Configuration and Functions
  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 Timing Requirements
    7. 6.7 Switching Characteristics
    8. 6.8 Timing Diagrams
    9. 6.9 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Input Voltage (VDD)
        1. 7.3.1.1 VDD Hysteresis
        2. 7.3.1.2 VDD Glitch Immunity
      2. 7.3.2 Implemented Window-Watchdog Settings
        1. 7.3.2.1 Timing Rules of Window-Watchdog
      3. 7.3.3 Watchdog Software Considerations
    4. 7.4 Device Functional Modes
  8. Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Lower-Boundary Calculation
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Programming Window-Watchdog Using an External Capacitor
      3. 8.2.3 Application Curve
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Device Nomenclature
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 接收文档更新通知
    4. 11.4 支持资源
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 术语表
  12. 12Mechanical, Packaging, and Orderable Information

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Programming Window-Watchdog Using an External Capacitor

The upper boundary of the watchdog timer can be set by an external capacitor connected between the WDT pin and GND. Common consumer electronic capacitors can be used to implement this feature. The capacitors that are used should have low ESR and low tolerances because the tolerances must be considered to perform the calculations. The first formula is used to calculate the upper window frame. After calculating the upper window frame, the lower boundary can be calculated. As in the last example, the most important values are the tboundary,max and twindow,min. The trigger pulse must fit into this window frame.

The external capacitor should have a value between a minimum of 155 pF and a maximum of 63 nF.

Equation 2. GUID-EA872324-AB72-4E16-8986-2E08F6364A29-low.gif
Table 8-2 Watchdog Upper-Boundary Capacitor Programming
SELECTED OPERATION MODEWINDOW FRAME
WDT = external capacitor C(ext)WDR = 0 V and WDR = VDDtwindow,max = 1.25 × twindow,typ
twindow,min = 0.75 × twindow,typ