SLUSCV5 May   2022 TPS92643-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 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 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Internal Regulator
      2. 7.3.2  Buck Converter Switching Operation
      3. 7.3.3  Bootstrap Supply
      4. 7.3.4  Switching Frequency and Adaptive On-Time Control
      5. 7.3.5  Minimum On-Time, Off-Time, and Inductor Ripple
      6. 7.3.6  LED Current Regulation and Error Amplifier
      7. 7.3.7  Start-Up Sequence
      8. 7.3.8  Analog Dimming and Forced Continuous Conduction Mode
      9. 7.3.9  External PWM Dimming and Input Undervoltage Lockout (UVLO)
      10. 7.3.10 Analog Pulse Width Modulator Circuit
      11. 7.3.11 Output Short and Open-Circuit Faults
      12. 7.3.12 Overcurrent Protection
      13. 7.3.13 Thermal Shutdown
      14. 7.3.14 Fault Indicator and Diagnostics Summary
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1  Duty Cycle Considerations
      2. 8.1.2  Switching Frequency Selection
      3. 8.1.3  LED Current Programming
      4. 8.1.4  Inductor Selection
      5. 8.1.5  Output Capacitor Selection
      6. 8.1.6  Input Capacitor Selection
      7. 8.1.7  Bootstrap Capacitor Selection
      8. 8.1.8  Bootstrap Resistor Selection
      9. 8.1.9  Compensation Capacitor Selection
      10. 8.1.10 Input Dropout and Undervoltage Protection
      11. 8.1.11 APWM Input and Thermal Protection
      12. 8.1.12 Protection Diodes
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  Calculating Duty Cycle
        2. 8.2.2.2  Calculating Minimum On-Time and Off-Time
        3. 8.2.2.3  Minimum Switching Frequency
        4. 8.2.2.4  LED Current Set Point
        5. 8.2.2.5  Inductor Selection
        6. 8.2.2.6  Output Capacitor Selection
        7. 8.2.2.7  Bootstrap Capacitor Selection
        8. 8.2.2.8  Bootstrap Resistor Selection
        9. 8.2.2.9  Compensation Capacitor Selection
        10. 8.2.2.10 VIN Dropout Protection and PWM Dimming
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Compact Layout for EMI Reduction
        1. 10.1.1.1 Ground Plane
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Receiving Notification of Documentation Updates
    2. 11.2 Support Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7.3.11 Output Short and Open-Circuit Faults

The TPS92643-Q1 monitors the CSN voltage to detect output short circuit faults. A short failure is indicated by open drain FLT output when the CSN voltage drops below 1.5 V (typical). The device continues to regulate current and operate without interruption in case of short circuit. A short-circuit fault does not impact the device behavior. The device continues to operate and regulate current without interruption.

An LED open-circuit fault ultimately causes the output voltage to increase and settle close to the input voltage. When this event occurs, the TPS92643-Q1 switching operation is then controlled by the fixed on-time and minimum off-time resulting in a duty cycle close to 100%. The COMP pin voltage exceeds the COMP overvoltage threshold, VCOMP(OV), and the fault in indicated by FLT output. However, during open circuit, the dynamic behavior of the device and buck converter is influenced by the input voltage, VIN, and the output capacitor, COUT, value. The device response to open circuit can be categorized into the following two distinct cases.

Case 1: For a Buck converter design with a small output capacitor, the switching operation in open load condition exits the tank resonance forcing the output voltage to oscillate. The frequency and amplitude of the oscillation are based on the resonant frequency and Q-factor of the second order tank network.

Figure 7-7 Open-Circuit Condition with Output Voltage Oscillation

Case 2: For a buck converter design with large output capacitor the inductor Q-factor and resonant frequency are much lower than the switching frequency. In this case, output voltage rises to input voltage and the converter continues to switch with minimum off-time.

Figure 7-8 Open-Circuit Condition with Minimum Off-Time Operation

The voltage transient imposed on CSP and CSN inputs during short circuit and open circuit is dependent on the output capacitance and is influenced by the cable harness impedance. The inductance associated with a long cable harness resonates with the charge stored on the output capacitor and forces CSP and CSN voltage to ring above VIN and below ground. The magnitude of the voltage overshoot above VIN and below ground are dependent on the parasitic cable harness inductance and resistance.

Figure 7-9 Cable Harness Parasitic Inductance

When using a long cable harness, TI recommends diodes to clamp the voltage across CSP and CSN input, as shown in Figure 7-10. TI recommends a low forward voltage Schottky diode or a fast recovery silicon diode with reverse blocking voltage rating greater than the maximum output voltage. The diode is required to be placed close to the output capacitor.

Figure 7-10 Transient Protection Using an External Diode