SNVSB03D December   2018  – January 2020

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Application Circuit
      2.      TPS3840 Typical Supply Current
  4. 4 Revision History
  5. 5 Device Comparison
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 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 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Input Voltage (VDD)
        1. 8.3.1.1 VDD Hysteresis
        2. 8.3.1.2 VDD Transient Immunity
      2. 8.3.2 User-Programmable Reset Time Delay
      3. 8.3.3 Manual Reset (MR) Input
      4. 8.3.4 Output Logic
        1. 8.3.4.1 RESET Output, Active-Low
        2. 8.3.4.2 RESET Output, Active-High
    4. 8.4 Device Functional Modes
      1. 8.4.1 Normal Operation (VDD > VDD(min))
      2. 8.4.2 VDD Between VPOR and VDD(min)
      3. 8.4.3 Below Power-On-Reset (VDD < VPOR)
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design 1: Dual Rail Monitoring with Power-Up Sequencing
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
        3. 9.2.1.3 Application Curves
      2. 9.2.2 Design 2: Battery Voltage and Temperature Monitor
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
      3. 9.2.3 Design 3: Fast Start Undervoltage Supervisor with Level-shifted Input
        1. 9.2.3.1 Design Requirements
        2. 9.2.3.2 Detailed Design Procedure
      4. 9.2.4 Design 4: Voltage Monitor with Back-up Battery Switchover
        1. 9.2.4.1 Design Requirements
        2. 9.2.4.2 Detailed Design Procedure
      5. 9.2.5 Application Curve: TPS3840EVM
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Nomenclature
    2. 12.2 Support Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

9.2.4.2 Detailed Design Procedure

The primary constraints for this application are choosing the correct device variant for the monitored voltage and deciding the preferred solution to switch the back-up battery in and out of the system. For this design, the TPS3840PL30 provides an active-low, push-pull output topology that turns on the PFET when the 5-V rail monitored by VDD drops to 3.0 V. The diodes logically OR the power supply with the back-up battery and prevents reverse current leakage. Using this solution, the System Output remains above 1.8 V in all circumstances unless both the 5-V rail and back-up battery fail. The System Output voltage will follow the 5-V rail minus a diode drop until the 5-V rail drops to 3 V then the back-up battery switches into the system providing 3.3 V minus a diode drop to the System Output. When the 5-V rail comes back above 3.1 V accounting for hysteresis, the PFET turns off to disconnect the back-up battery from the system. Since this design disconnects the battery when not being used, this solution maximizes battery life.