SLVSH72B December   2023  – October 2026 TPS281C100

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Options
  6. 5 Pin Configuration and Functions
  7. 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 SNS Timing Characteristics
    7. 6.7 Switching Characteristics
    8. 6.8 Typical Characteristics
  8. 7 Parameter Measurement Information
  9. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Device Functional Modes
    4. 8.4 Working Mode
    5. 8.5 Feature Description
      1. 8.5.1 Accurate Current Sense
        1. 8.5.1.1 High Accuracy Sense Mode
      2. 8.5.2 Programmable Current Limit
        1. 8.5.2.1 Short-Circuit and Overload Protection
        2. 8.5.2.2 Capacitive Charging
      3. 8.5.3 Inductive-Load Switching-Off Clamp
      4. 8.5.4 Inductive Load Demagnetization
      5. 8.5.5 Full Protections and Diagnostics
        1. 8.5.5.1 Open-Load Detection
        2. 8.5.5.2 Thermal Protection Behavior
        3. 8.5.5.3 Undervoltage Lockout (UVLO) Protection
        4. 8.5.5.4 Reverse Polarity Protection
          1. 8.5.5.4.1 Method 1
          2. 8.5.5.4.2 Method 2 (GND Network Protection)
        5. 8.5.5.5 Protection for MCU I/Os
        6. 8.5.5.6 Diagnostic Enable Function
        7. 8.5.5.7 Loss of Ground
  10. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
        1. 9.2.1.1 IEC 61000-4-4 EFT
        2. 9.2.1.2 IEC 61000-4-5 Surge
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Selecting RILIM
        2. 9.2.2.2 Selecting RSNS
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
        1. 9.4.1.1 EMC Considerations
      2. 9.4.2 Layout Example
        1. 9.4.2.1 DNT Layout Without a GND Network
      3. 9.4.3 Thermal Considerations
  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. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information

8.5.1 Accurate Current Sense

The current-sense function is internally implemented, which allows a better real-time monitoring effect and more-accurate diagnostics without further calibration. Use a current mirror to source 1 / KSNS of the load current, flowing out to the external resistor between the SNS pin and GND, and reflected as voltage on the SNS pin.

KSNS is the ratio of the output current and the sense current. The accuracy values of KSNS quoted in the electrical characteristics do take into consideration temperature and supply voltage. Each device is internally calibrated while in production, so post-calibration by users is not required in most cases.

The maximum voltage out on the SNS pin is clamped to VSNSFH which is the fault voltage level. To establish that this voltage is not higher than the system can tolerate, TI correlates the voltage coming in on the DIAG_EN pin with the maximum voltage out on the SNS pin. If DIAG_EN is between VIH and 3.3V, the maximum output on the SNS pin is approximately 3.3V. However, if the voltage at DIAG_EN is above 3.3V, then the fault SNS voltage, VSNSFH, tracks that voltage up to 5V. This is done because the GPIO voltage output that is powering the diagnostics through DIAG_EN, is close to the maximum acceptable ADC voltage within the same microcontroller. Therefore, select the sense resistor value, RSNS, to maximize the range of currents the system must measure. Select the RSNS value based on application need. The maximum usable RSNS value is bounded by the ADC minimum acceptable voltage, VADC,min, for the smallest load current needed to be measured by the system, ILOAD,min. The minimum acceptable RSNS value has to confirm the VSNS voltage is below the VSNSFH value so that the system can determine faults. This difference between the maximum readable current through the SNS pin, ILOAD,max × RSNS, and the VSNSFH is called the headroom voltage, VHR. The system determines the headroom voltage, but is important so that there is a difference between the maximum readable current and a fault condition. Therefore, the minimum RSNS value must be the VSNSFH minus the VHR times the sense current ratio, KSNS divided by the maximum load current the system must measure, ILOAD,max. This boundary equation is Equation 1.

Equation 1. V ADC,min × K SNS / I LOAD,min ≤ R SNS ≤ ( V SNSFH − V HR ) × K SNS / I LOAD,max
TPS281C100 Voltage Indication on the Current-Sense PinFigure 8-2 Voltage Indication on the Current-Sense Pin

The maximum current the system wants to read, ILOAD,max, must be below the current limit threshold because once the current limit threshold is tripped the VSNS value goes to VSNSFH. Additionally, currents being measured must be below 4A to confirm that the current sense output is not saturated.

TPS281C100 Current-Sense and Current-Limit Block DiagramFigure 8-3 Current-Sense and Current-Limit Block Diagram

Since this scheme adapts based on the voltage coming in from the MCU. There is no need to have a zener diode on the SNS pin to protect from high voltages.