SLVSFZ1 December   2020 TPS27SA08-Q1


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Summary Table
  6. Pin Configuration and Functions
    1. 6.1 Recommended Connections for Unused Pins
  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 Switching Characteristics
    7. 7.7 SNS Timing Characteristics
    8. 7.8 Typical Characteristics
  8. Parameter Measurement Information
  9. Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Protection Mechanisms
        1. Thermal Shutdown
        2. Current Limit
          1. Current Limit Foldback
          2. Undervoltage Lockout (UVLO)
          3. VBB during Short-to-Ground
        3. Energy Limit
        4. Voltage Transients
          1. Driving Inductive and Capacitive Loads
        5. Reverse supply
        6. Fault Event – Timing Diagrams
      2. 9.3.2 Diagnostic Mechanisms
        1. VOUT Short-to-supply and Open-Load
          1. Detection With Switch Enabled
          2. Detection With Switch Disabled
        2. SNS Output
          1. RSNS Value
            1. High Accuracy Load Current Sense
            2. SNS Output Filter
        3. ST Pin
        4. Fault Indication and SNS Mux
        5. Resistor Sharing
        6. High-Frequency, Low Duty-Cycle Current Sensing
    4. 9.4 Device Functional Modes
      1. 9.4.1 Off
      2. 9.4.2 Standby
      3. 9.4.3 Diagnostic
      4. 9.4.4 Standby Delay
      5. 9.4.5 Active
      6. 9.4.6 Fault
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Ground Protection Network
      2. 10.1.2 Interface With Microcontroller
      3. 10.1.3 I/O Protection
      4. 10.1.4 Inverse Current
      5. 10.1.5 Loss of GND
      6. 10.1.6 Thermal Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. Thermal Considerations
        2. Diagnostics
          1. Selecting the RISNS Value
      3. 10.2.3 Application Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Related Documentation
    2. 13.2 Trademarks
    3. 13.3 Electrostatic Discharge Caution
    4. 13.4 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

Application Curves

Figure 10-4 shows the behavior of the TPS27SA08-Q1 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.

GUID-995A90D8-7BE0-4CDD-8BFC-E0D2438B7322-low.gifFigure 10-4 Heater Turn-on Time

By measuring the voltage on the SNS pin, the TPS27SA08-Q1 device can communicate back to the system MCU what the load current is. Figure 10-5 shows that when the seat heater approaches full load and IOUT jumps from a low load current of 1 A up to a 5-A load current, the load step is mirrored on the SNS pin.

GUID-6A6EF28F-850C-446A-8320-E05FCD08693F-low.gifFigure 10-5 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 ideal for the TPS27SA08-Q1 device to recognize that the load has been removed and report a FLT to the MCU. Figure 10-6 shows the behavior of the TPS27SA08-Q1 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.

GUID-A60B669A-03AB-41B5-B02E-A5EFDB339A1A-low.gifFigure 10-6 Open Load Detection if Heating Element is Missing

Importantly, the TPS27SA08-Q1 device will also protect the system in the event of a short-circuit. Figure 10-7 shows the behavior of the device if it is enabled into a short circuit condition. The current will be clamped to near the current limit threshold (ICL) until it hits an over temperature event, at which point the FET will be turned off. In this way, the system is protected from unchecked overcurrent in the event of a short circuit.

GUID-72F4C0F2-C46F-46D4-ADE6-D72F14080856-low.gifFigure 10-7 Overcurrent Behavior During Short Circuit Event