SNVSBI5A July   2019  – September 2019 TPS3870-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Integrated Overvoltage Detection
      2.      Typical Overvoltage Accuracy Distribution
  4. 4 Revision History
  5. 5 Device Comparison Table
  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 VDD
      2. 8.3.2 SENSE
      3. 8.3.3 RESET
      4. 8.3.4 Capacitor Time (CT)
      5. 8.3.5 Manual Reset (MR)
    4. 8.4 Device Functional Modes
      1. 8.4.1 Normal Operation (VDD > VDD(MIN))
      2. 8.4.2 Undervoltage Lockout (VPOR < VDD < UVLO)
      3. 8.4.3 Power-On Reset (VDD < VPOR)
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Voltage Threshold Accuracy
      2. 9.1.2 CT Reset Time Delay
        1. 9.1.2.1 Factory-Programmed Reset Delay Timing
        2. 9.1.2.2 Programmable Reset Delay-Timing
      3. 9.1.3 RESET Latch Mode
      4. 9.1.4 Adjustable Voltage Thresholds
      5. 9.1.5 Immunity to SENSE Pin Voltage Transients
        1. 9.1.5.1 Hysteresis
    2. 9.2 Typical Application
      1. 9.2.1 Design 1: RESET Latch Mode
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
        3. 9.2.1.3 Application Curves
  10. 10Power Supply Recommendations
    1. 10.1 Power Supply Guidelines
  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 Documentation Support
      1. 12.2.1 Evaluation Module
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Support Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

9.1.4 Adjustable Voltage Thresholds

The TPS3870-Q1 0.7% maximum accuracy allows for adjustable voltage thresholds using external resistors without adding major inaccuracies to the device. In case that the desired monitored voltage is not available, external resistor dividers can be used to set the desired voltage thresholds. Figure 23 illustrates an example of how to adjust the voltage threshold with external resistor dividers. The resistors can be calculated depending on the desired voltage threshold and device part number. TI recommends using the 0.8V voltage threshold device such as the TPS3870J4080 because of the bypass mode of internal resistor ladder.

For example, consider a 2.0 V rail being monitored (VMON) using the TPS3870J4080 variant. Using Equation 4, R1 = 15 kΩ given that R2 = 10 kΩ, VMON = 2 V , and VSENSE = 0.8 V. This device is typically meant to monitor a 0.8 V rail with a +4% voltage threshold. This means that the device overvoltage threshold (VIT+(OV)) is 0.832 V. Using Equation 4, the monitored overvoltage threshold (VMON+) = 2.08 V when VSENSE = VIT+(OV). If a wider tolerance threshold is desired, use a device variant shown on Table 6 to determine what device part number matches your application.

Equation 4. VSENSE = VMON × (R2 ÷ (R1 + R2))

There are inaccuracies that must be taken into consideration while adjusting voltage thresholds. Aside from the tolerance of the resistor divider, there is an internal resistance of the SENSE pin that may affect the accuracy of the resistor divider. Although expected to be very high impedance, users are recommended to calculate the values for design specifications. The internal sense resistance (RSENSE) can be calculated by the sense voltage (VSENSE) divided by the sense current (ISENSE) as shown in Equation 6. VSENSE can be calculated using Equation 4 depending on the resistor divider and monitored voltage. ISENSE can be calculated using Equation 5.

Equation 5. ISENSE = (VMON – VSENSE) ÷ R1 – (VSENSE ÷ R2)
Equation 6. RSENSE = VSENSE ÷ ISENSE
TPS3870-Q1 External-Voltage-Divider.gifFigure 23. Adjustable Voltage Threshold with External Resistor Dividers

Although Equation 4 solves for VSENSE, inaccuracies for leakage need to be taken into consideration when understanding the overall threshold accuracy of the device. To calculate the threshold with this inaccuracy taken into account, use Equation 7

Equation 7. VIT_Actual = VSENSE + R1 × ((VSENSE ÷ R2) + ISENSE)

To calculate the worst case values through the resistor divider, ISENSE should be taken from the Electrical Characteristics table. While these equations provide a summary of what you need to correctly account for factors that go into determining your resistor divider with inaccuracy, you should use the Application Report Optimizing Resistor Dividers at a Comparator Input to further understand this and to design your implementation. This report explains how to optimize the resistor divider at the SENSE input for an adjustable voltage threshold version of the device. You should follow this Application Report using 0.8 V as the VREF value for the TPS3870-Q1.