SLVSFJ6A November   2020  – June 2026 TPS27SA08

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Summary Table
  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 Switching Characteristics
    7. 6.7 SNS Timing 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 Feature Description
      1. 8.3.1 Protection Mechanisms
        1. 8.3.1.1 Thermal Shutdown
        2. 8.3.1.2 Current Limit
          1. 8.3.1.2.1 Current Limit Foldback
          2. 8.3.1.2.2 Undervoltage Lockout (UVLO)
          3. 8.3.1.2.3 VBB during Short-to-Ground
        3. 8.3.1.3 Energy Limit
        4. 8.3.1.4 Voltage Transients
          1. 8.3.1.4.1 Driving Inductive and Capacitive Loads
        5. 8.3.1.5 Reverse Supply
        6. 8.3.1.6 Fault Event – Timing Diagrams
      2. 8.3.2 Diagnostic Mechanisms
        1. 8.3.2.1 VOUT Short-to-supply and Open-Load
          1. 8.3.2.1.1 Detection With Switch Enabled
          2. 8.3.2.1.2 Detection With Switch Disabled
        2. 8.3.2.2 SNS Output
          1. 8.3.2.2.1 RSNS Value
            1. 8.3.2.2.1.1 High Accuracy Load Current Sense
            2. 8.3.2.2.1.2 SNS Output Filter
        3. 8.3.2.3 ST Pin
        4. 8.3.2.4 Fault Indication and SNS Mux
        5. 8.3.2.5 Resistor Sharing
        6. 8.3.2.6 High-Frequency, Low Duty-Cycle Current Sensing
    4. 8.4 Device Functional Modes
      1. 8.4.1 Off
      2. 8.4.2 Standby
      3. 8.4.3 Diagnostic
      4. 8.4.4 Standby Delay
      5. 8.4.5 Active
      6. 8.4.6 Fault
  10. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Ground Protection Network
      2. 9.1.2 Interface With Microcontroller
      3. 9.1.3 I/O Protection
      4. 9.1.4 Inverse Current
      5. 9.1.5 Loss of GND
      6. 9.1.6 Thermal Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Thermal Considerations
        2. 9.2.2.2 Diagnostics
          1. 9.2.2.2.1 Selecting the RISNS Value
      3. 9.2.3 Application Curves
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
      2. 9.4.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Related Documentation
    2. 10.2 Trademarks
    3. 10.3 Electrostatic Discharge Caution
    4. 10.4 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information

9.2.3 Application Curves

Figure 9-4 shows the behavior of the TPS27SA08 device in this application when the MCU provides an enable pulse to beginning heating the resistive element. Shortly after the EN pin goes high, the load current begins to flow and the SNS pin measures the output current.

TPS27SA08 Heater Turn-on TimeFigure 9-4 Heater Turn-on Time

By measuring the voltage on the SNS pin, the TPS27SA08 device can communicate back to the system MCU what the load current is. Figure 9-5 shows that when the seat heater approaches full load and IOUT jumps from a low load current of 1A up to a 5A load current, the load step is mirrored on the SNS pin.

TPS27SA08 SNS Response During Heater Load StepFigure 9-5 SNS Response During Heater Load Step

One common concern in these type of applications is that the heating element can accidentally lose connection, creating an open load situation. In this case, it is best for the TPS27SA08 device to recognize that the load has been removed and report a FLT to the MCU. Figure 9-6 shows the behavior of the TPS27SA08 device when there is no load attached. As soon as the DIAG_EN pin is engaged, the SNS output goes high and the ST output engages low. By monitoring these pins, the MCU can recognize there is a fault and notify the user that maintenance is required.

TPS27SA08 Open Load Detection If Heating Element is MissingFigure 9-6 Open Load Detection If Heating Element is Missing

Importantly, the TPS27SA08 device also protects the system in the event of a short circuit. Figure 9-7 shows the behavior of the device if it is enabled into a short circuit condition. The current is clamped to near the current limit threshold (ICL) until it hits an over temperature event, at which point the FET is turned off. In this way, the system is protected from unchecked overcurrent in the event of a short circuit.

TPS27SA08 Overcurrent Behavior During Short Circuit EventFigure 9-7 Overcurrent Behavior During Short Circuit Event