SLVSH18 December   2024 TPS4HC120-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
    1.     6
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 SNS Timing Characteristics
    7. 5.7 Switching Characteristics
    8. 5.8 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Pin Current and Voltage Conventions
      2. 6.3.2 Low Power Mode
      3. 6.3.3 Accurate Current Sense
      4. 6.3.4 Adjustable Current Limit
      5. 6.3.5 Inductive-Load Switching-Off Clamp
      6. 6.3.6 Fault Detection and Reporting
        1. 6.3.6.1 Diagnostic Enable Function
        2. 6.3.6.2 Multiplexing of Current Sense
        3. 6.3.6.3 FAULT Reporting
        4. 6.3.6.4 Fault Table
      7. 6.3.7 Full Diagnostics
        1. 6.3.7.1 Short-to-GND and Overload Detection
        2. 6.3.7.2 Open-Load Detection
          1. 6.3.7.2.1 Channel On
          2. 6.3.7.2.2 Channel Off
        3. 6.3.7.3 Short-to-Battery Detection
        4. 6.3.7.4 Reverse-Polarity and Battery Protection
        5. 6.3.7.5 Thermal Fault Detection
          1. 6.3.7.5.1 Thermal Protection Behavior
      8. 6.3.8 Full Protections
        1. 6.3.8.1 UVLO Protection
        2. 6.3.8.2 Loss of GND Protection
        3. 6.3.8.3 Loss of Power Supply Protection
        4. 6.3.8.4 Reverse Polarity Protection
        5. 6.3.8.5 Protection for MCU I/Os
    4. 6.4 Device Functional Modes
      1. 6.4.1 Working Mode
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
      3. 7.2.3 Application Curves
    3. 7.3 EMC Transient Disturbances Test
    4. 7.4 Power Supply Recommendations
    5. 7.5 Layout
      1. 7.5.1 Layout Guidelines
      2. 7.5.2 Layout Examples
        1. 7.5.2.1 Without a GND Network
        2. 7.5.2.2 With a GND Network
  9. 8 Device and Documentation Support
    1. 8.1 Receiving Notification of Documentation Updates
    2. 8.2 Support Resources
    3. 8.3 Trademarks
    4. 8.4 Electrostatic Discharge Caution
    5. 8.5 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

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

6.3.3 Accurate Current Sense

The high-accuracy 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. To make sure that this voltage is not higher than the system can tolerate, the max voltage at the DIAG_EN pin has been limited to the voltage at 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. Tracking 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, the sense resistor value, RSNS, can be chosen to maximize the range of currents needed to be measured by the system. The RSNS value must 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 correctly 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 must measure, ILOAD,max. Use the following equation to set the boundary equation.

Equation 1. VADC,min × KSNS / ILOAD,min ≤ RSNS ≤ (VSNSFH – VHR) × KSNS / ILOAD,max
TPS4HC120-Q1 Voltage Indication on the Current-Sense Pin Figure 6-5 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 after the current-limit threshold is tripped the VSNS value goes to VSNSFH.

TPS4HC120-Q1 Current-Sense and Current-Limit Block DiagramFigure 6-6 Current-Sense and Current-Limit Block Diagram

Because 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.