ZHCSO18A december   2022  – june 2023 TPS281C30

PRODUCTION DATA  

  1.   1
  2. 1 特性
  3. 2 应用
  4. 3 说明
  5. 4 Revision History
  6. 5 Device Comparison Table
  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 Thermal Information
    6. 7.6 Electrical Characteristics
    7. 7.7 SNS Timing Characteristics
    8. 7.8 Switching Characteristics
    9. 7.9 Typical Characteristics
  9. 8 Parameter Measurement Information
  10. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Device Functional Modes
      1. 9.3.1 Working Mode
    4. 9.4 Feature Description
      1. 9.4.1 Accurate Current Sense
        1. 9.4.1.1 High Accuracy Sense Mode
      2. 9.4.2 Programmable Current Limit
        1. 9.4.2.1 Short-Circuit and Overload Protection
        2. 9.4.2.2 Capacitive Charging
      3. 9.4.3 Inductive-Load Switching-Off Clamp
      4. 9.4.4 Inductive Load Demagnetization
      5. 9.4.5 Full Protections and Diagnostics
        1. 9.4.5.1 Open-Load Detection
        2. 9.4.5.2 Thermal Protection Behavior
        3. 9.4.5.3 Undervoltage Lockout (UVLO) Protection
        4. 9.4.5.4 Overvoltage (OVP) Protection
        5. 9.4.5.5 Reverse Polarity Protection
        6. 9.4.5.6 Protection for MCU I/Os
        7. 9.4.5.7 Diagnostic Enable Function
        8. 9.4.5.8 Loss of Ground
  11. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
        1. 10.2.1.1 IEC 61000-4-5 Surge
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Selecting RILIM
        2. 10.2.2.2 Selecting RSNS
    3. 10.3 Power Supply Recommendations
    4. 10.4 Layout
      1. 10.4.1 Layout Guidelines
        1. 10.4.1.1 EMC Considerations
      2. 10.4.2 Layout Example
        1. 10.4.2.1 PWP Layout without a GND Network
        2. 10.4.2.2 PWP Layout with a GND Network
        3. 10.4.2.3 RGW Layout with a GND Network
      3. 10.4.3 Thermal Considerations
  12. 11Device and Documentation Support
    1. 11.1 接收文档更新通知
    2. 11.2 支持资源
    3. 11.3 Trademarks
    4. 11.4 静电放电警告
    5. 11.5 术语表
  13. 12Mechanical, Packaging, and Orderable Information

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9.4.1 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. A current mirror is used 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 was 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. In order to make sure that this voltage is not higher than the system can tolerate, TI has correlated 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 3.3 V, the maximum output on the SNS pin will be ~3.3 V. However, if the voltage at DIAG_EN is above 3.3 V, then the fault SNS voltage, VSNSFH, will track that voltage up to 5 V. This is done because the GPIO voltage output that is powering the diagnostics through DIAG_EN, will be close to the maximum acceptable ADC voltage within the same microcontroller. Therefore, the sense resistor value, RSNS, can be chosen to maximize the range of currents needed to be measured by the system. The RSNS value should be chosen 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 ensure 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 headroom voltage is determined by the system but is important so that there is a difference between the maximum readable current and a fault condition. Therefore, the minimum RSNS value has to be the VSNSFH minus the VHR times the sense current ratio, KSNS divided by the maximum load current the system needs to measure, ILOAD,max. This boundary equation can be seen in Equation 1.

Equation 1. VADC,min × KSNS / ILOAD,min ≤ RSNS ≤ (VSNSFH – VHR) × KSNS / ILOAD,max
GUID-F6E1D63B-55F8-4CFD-9F3C-FA51469E3797-low.svg Figure 9-2 Voltage Indication on the Current-Sense Pin

The maximum current the system wants to read, ILOAD,max, needs to be below the current limit threshold because once the current limit threshold is tripped the VSNS value will go to VSNSFH. Additionally, currents being measured should be below 7 A to ensure that the current sense output is not saturated.

GUID-20210531-CA0I-8L7D-8Z3X-KSMR81M1MJQG-low.svg Figure 9-3 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.