SBVS285 February   2017 TPS3852-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Application Circuit
      2.      Undervoltage Threshold (VITN) Accuracy vs Temperature
  4. 4 Revision History
  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 Timing Requirements
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 RESET
      2. 7.3.2 Manual Reset (MR)
      3. 7.3.3 Undervoltage Fault Detection
      4. 7.3.4 Watchdog Mode
        1. 7.3.4.1 SET1
        2. 7.3.4.2 Window Watchdog Timer
        3. 7.3.4.3 Watchdog Input (WDI)
        4. 7.3.4.4 CWD
        5. 7.3.4.5 Watchdog Output (WDO)
    4. 7.4 Device Functional Modes
      1. 7.4.1 VDD is Below VPOR (VDD < VPOR)
      2. 7.4.2 Above Power-On-Reset, But Less Than VDD(min) (VPOR ≤ VDD < VDD(min))
      3. 7.4.3 Normal Operation (VDD ≥ VDD(min))
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 CWD Functionality
        1. 8.1.1.1 Factory-Programmed Timing Options
        2. 8.1.1.2 Adjustable Capacitor Timing
      2. 8.1.2 Overdrive Voltage
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Monitoring the 3.3-V Rail
        2. 8.2.2.2 Calculating RESET and the WDO Pullup Resistor
        3. 8.2.2.3 Setting the Window Watchdog
        4. 8.2.2.4 Watchdog Disabled During Initialization Period
      3. 8.2.3 Glitch Immunity
      4. 8.2.4 Application Curves
  9. 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 Development Support
        1. 11.1.1.1 Evaluation Module
      2. 11.1.2 Device Nomenclature
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • DRB|8
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.1.1.2 Adjustable Capacitor Timing

Adjustable capacitor timing is achievable by connecting a capacitor to the CWD pin. If a capacitor is connected to CWD, then a 375-nA current source charges CCWD until VCWD = 1.21 V. The TPS3852-Q1 determines the window watchdog upper boundary with the formula given in Equation 1, where CCWD is in microfarads (µF) and tWDU is in seconds.

Equation 1. tWDU(typ)(s) = 77.4 × CCWD(µF) + 0.055 (s)

The TPS3852-Q1 is limited to using CCWD capacitors between 100 pF and 1 µF. Note that Equation 1 is for ideal capacitors; capacitor tolerances cause the actual device timing to vary. For the most accurate timing, use ceramic capacitors with COG dielectric material. As shown in Table 3, when using the minimum capacitance of 100 pF, the watchdog upper boundary is 62.74 ms; whereas with a 1-µF capacitance, the watchdog upper boundary is 77.455 seconds. If a CCWD capacitor is used, Equation 1 can be used to set the window watchdog upper boundary (tWDU). Table 4 shows how tWDU can be used to calculate tWDL.

Table 3. tWDU Values for Common Ideal Capacitor Values

CCWDWATCHDOG UPPER BOUNDARY (tWDU)UNIT
MIN(1)TYPMAX(1)
100 pF 53.32 62.74 72.15 ms
1 nF 112.5 132.4 152.2 ms
10 nF 704 829 953 ms
100 nF 6625 7795 8964 ms
1 µF 65836 77455 89073 ms
(1) Minimum and maximum values are calculated using ideal capacitors.

Table 4. Programmable CWD Timing

INPUTWATCHDOG LOWER BOUNDARY (tWDL)WATCHDOG UPPER BOUNDARY (tWDU)UNIT
CWDSET1MINTYPMAXMINTYPMAX
CCWD 0 Watchdog disabled Watchdog disabled
1 tWDU(min) x 0.5 tWDU x 0.5 tWDU(max) x 0.5 0.85 x tWDU(typ) tWDU(typ)(1) 1.15 x tWDU(typ) s
(1) Calculated from Equation 1 using ideal capacitors.