SLVSCK5C September   2014  – January 2020 TPS92638-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Typical Application Schematic
  5. 5 Revision History
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 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 Typical Characteristics
  8. 8 Parameter Measurement Information
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 LED Current Setting
      2. 9.3.2 PWM Control
      3. 9.3.3 Fault Diagnostics
        1. 9.3.3.1 Open-Load Detection
      4. 9.3.4 Thermal Foldback
    4. 9.4 Device Functional Modes
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Applications
      1. 10.2.1 PWM Dimming by Bank
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedure
        3. 10.2.1.3 Application Performance Plots
      2. 10.2.2 Two Brightness Levels for TAIL and STOP Lights
        1. 10.2.2.1 Design Requirements
        2. 10.2.2.2 Detailed Design Procedure
      3. 10.2.3 PWM Dimming by Modulated Supply
        1. 10.2.3.1 Design Requirements
        2. 10.2.3.2 Design Procedure
      4. 10.2.4 Driving LEDs From a Single Device With Channels in Parallel
        1. 10.2.4.1 Design Requirements
        2. 10.2.4.2 Design Procedure
      5. 10.2.5 Driving LEDs From Multiple Devices With Channels in Parallel
        1. 10.2.5.1 Design Requirements
        2. 10.2.5.2 Design Procedure
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
    3. 12.3 Thermal Information
  13. 13Device and Documentation Support
    1. 13.1 Trademarks
    2. 13.2 Electrostatic Discharge Caution
    3. 13.3 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

9.3.3 Fault Diagnostics

The TPS92638-Q1 device has a fault pin, FAULT, which is for the short, open, and thermal-shutdown general faults. This arrangement allows the maximum flexibility based on all requirements and application conditions.

Connection the device FAULT pin to the MCU allows for fault reporting. The FAULT pin is an open-drain transistor with a weak internal pullup.

The device releases the FAULT bus when external circuitry toggles the FAULT bus, or on a power cycle of the device. In an application that has no MCU, only cycling power clears the fault.

The following faults result in the FAULT pin going low: thermal shutdown, open load, or output short circuit. For thermal shutdown and open LED, release of the FAULT pin occurs when the thermal shutdown or open-LED condition no longer exists. For other faults, the FAULT pin remains low even after the condition does not exist, and clearing is only possible by toggling FAULT or by power cycling of the device.

TPS92638-Q1 det_tim_dia_1_SLVSCK5.gifFigure 32. TPS92638-Q1 Device Fault-Handling Behavior, FAULT Bus Floating

The design of an application with no MCU allows the connecting together of up to 15 TPS92638-Q1 FAULT̅ pins. When one or more devices have errors, their corresponding FAULT̅ pins go low, thus pulling down the connected FAULT bus and shutting down all device outputs. Figure 33 illustrates the FAULT line bus connection.

TPS92638-Q1 fau_lin_conn_SLVSCK5.gifFigure 33. Connection of FAULT Line Bus

The device releases the FAULT bus by external circuitry pulling the FAULT bus high, by toggling of the EN pin, or by a power cycle of the device. In an application without an MCU, only a power cycle clears the fault. Figure 34 is a detailed timing diagram.

TPS92638-Q1 det_tim_dia_2_SLVSCK5.gifFigure 34. TPS92638-Q1 Device Fault-Handling Behavior, FAULT Bus Externally Pulled High

Table 2. Fault Table

FAILURE MODE JUDGMENT CONDITION DIAGNOSTIC OUTPUT PIN(1) ACTION FAULT DEVICE REACTION FAILURE REMOVED SELF CLEARING
DETECTION VOLTAGE CHANNEL STATUS DETECTION MECHANISM
Short Circuit:
1 or several LED strings		 V(SUPPLY) > 5 V On V(IOUTx) < 0.9 V FAULT Pulled low Externally
pulled high		 Failing strings turned off,
other CHs on		 Toggle EN,
power cycle		 No
Floating All strings turned OFF Toggle EN,
power cycle
Open Load:
1 or several LED strings		 V(SUPPLY) > 5 V On V(SUPPLY) – V(IOUTx) < 100 mV FAULT Pulled low Externally
pulled high		 All strings stay ON Failure condition removed Yes
Floating Failing strings stay ON,
other CHs turned OFF		 Failure condition removed
Short to Battery:
1 or several LED strings		 V(SUPPLY) > 5 V On or off V(SUPPLY) – V(IOUTx) < 100 mV FAULT Pulled low Externally
pulled high		 All strings stay ON Failure condition removed Yes
Floating Failing strings stay ON,
other CHs turned OFF		 Failure condition removed
Thermal Shutdown V(SUPPLY) > 5 V On or off > 170°C FAULT Pulled low Externally
pulled high		 All strings turned OFF Temperature < 155°C Yes
Floating
Thermal Foldback V(SUPPLY) > 5 V On or off > 110°C N/A None N/A Reduced current to all strings Temperature < 100°C Yes
Reference Resistor Short V(SUPPLY) > 5 V On or off R(ref) < 1400 Ω FAULT Pulled low N/A All strings turned off Toggle EN, power cycle No
(1) If tying the diagnostic FAULT pin high externally, the pullup must be strong enough to override the internal pulldown.