SLVSGF0A october   2022  – june 2023 TPS3435-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Revision History
  6. 5 Device Comparison
  7. 6 Pin Configuration and Functions
  8. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Timing Requirements
    7. 7.7 Switching Characteristics
    8. 7.8 Timing Diagrams
    9. 7.9 Typical Characteristics
  9. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagrams
    3. 8.3 Feature Description
      1. 8.3.1 Timeout Watchdog Timer
        1. 8.3.1.1 tWD Timer
        2. 8.3.1.2 Watchdog Enable Disable Operation
        3. 8.3.1.3 tSD Watchdog Start Up Delay
        4. 8.3.1.4 SET Pin Behavior
      2. 8.3.2 Manual RESET
      3. 8.3.3 WDO Output
    4. 8.4 Device Functional Modes
  10. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Output Assert Delay
        1. 9.1.1.1 Factory-Programmed Output Assert Delay Timing
        2. 9.1.1.2 Adjustable Capacitor Timing
      2. 9.1.2 Watchdog Timer Functionality
        1. 9.1.2.1 Factory-Programmed Timing Options
        2. 9.1.2.2 Adjustable Capacitor Timing
    2. 9.2 Typical Applications
      1. 9.2.1 Design 1: Monitoring a Standard Microcontroller for Timeouts
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Setting the Watchdog Timeout Period
          2. 9.2.1.2.2 Setting Output Assert Delay
          3. 9.2.1.2.3 Setting the Startup Delay
          4. 9.2.1.2.4 Calculating the WDO Pullup Resistor
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
      2. 9.4.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Receiving Notification of Documentation Updates
    2. 10.2 Support Resources
    3. 10.3 Trademarks
    4. 10.4 Electrostatic Discharge Caution
    5. 10.5 Glossary
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.3.1.1 tWD Timer

The tWD timer for TPS3435-Q1 can be set using an external capacitor connected between CWD pin and GND pin. This feature is available with pinout options A or B. Applications which are space constrained or need timer values which meet offered timer options, can benefit when using pinout options C. The TPS3435-Q1 offers multiple fixed timer options ranging from 1 msec up-to 100 sec.

The TPS3435-Q1, when using capacitance based timer, senses the capacitance value during the power up. The capacitor is charged and discharged with known internal current source for one cycle to sense the capacitance value. The sensed value is used to arrive at tWD timer for the watchdog operation. This unique implementation helps reduce the continuous charge and discharge current for the capacitor, thus reducing overall current consumption. Continuous charge and discharge of capacitance creates wider dead time (no watchdog monitor functionality) when capacitor is discharging. The dead time is higher for high value of capacitance. The unique implementation of TPS3435-Q1 helps avoid the dead time as the capacitance is not continuously charging or discharging under normal operation. Ensure CCWD is < 200 x CCRST for accurate calibration of capacitance. Equation 1 highlights the relationship between tWD in second and CWD capacitance in farad. The tWD timer is 20% accurate for an ideal capacitor. Accuracy of the capacitance will have additional impact on the tWD time. Ensure the capacitance meets the recommended operating range. Capacitance outside the recommended range can lead to incorrect operation of the device.

Equation 1. tWD (sec) = 4.95 x 106 x CCWD (F)

The TPS3435-Q1 also offers wide selection of high accuracy fixed timer options starting from 1 msec to 100 sec including various industry standard values. The TPS3435-Q1 fixed time options are ±10% accurate for tWD ≥ 10 msec. For tWD < 10 msec, the accuracy is ±20%. tWD value relevant to application can be identified from the orderable part number. Refer Section 5 section to identify mapping of orderable part number to tWD value.

The TPS3435-Q1 offers flexibility to change the tWD value on the fly by controlling the logic levels on the SETx pins. Section 8.3.1.4 section explains the advantages offered by this feature and the device behavior with various SETx pin combinations.