SLDS237B January   2018  – January  2020 TPS92612-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Typical Application Diagram
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin 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 Timing Requirements
    7. 6.7 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 Device Bias
        1. 7.3.1.1 Power-On Reset (POR)
      2. 7.3.2 Constant-Current Driver
      3. 7.3.3 PWM Dimming
      4. 7.3.4 Protection
        1. 7.3.4.1 Short-to-GND Protection
        2. 7.3.4.2 Overtemperature Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 Undervoltage Lockout, V(SUPPLY)< V(POR_rising)
      2. 7.4.2 Normal Operation, V(SUPPLY) ≥ 4.5 V
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Single-Channel LED Driver
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curve
      2. 8.2.2 Single-Channel LED Driver With Heat Sharing
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
        3. 8.2.2.3 Application Curve
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

8.2.2.2 Detailed Design Procedure

In linear LED driver applications, the input voltage variation contributes to most of the thermal concerns. The resistor current, as indicated by Ohm’s law, depends on the voltage across the external resistors. The TPS92612-Q1 device controls the driver current I(DRIVE) to attain the desired total current. If I(P) increases, the TPS92612-Q1 device decreases I(DRIVE) to compensate, and vice versa.

While in low-dropout mode, the voltage across the R(P) resistor may be close to zero, so that almost no current can flow through the external resistor R(P).

When the input voltage is high, parallel-resistor current I(P) is proportional to the voltage across the parallel resistor, R(P). The parallel resistor, R(P), takes the majority of the total string current, generating maximum heat. The device must prevent current from draining out to ensure current regulation capability.

In this case, the parallel resistor value must be carefully calculated to ensure that 1) enough output current is achieved in low-dropout mode, 2) thermal dissipation for both the TPS92612-Q1 device and the resistor is within their thermal dissipation limits, and 3) device current in the high-voltage mode is above the minimal output-current requirement.

TI recommends to add capacitors C1 and C2 at SUPPLY and OUT. TI recommends C1 of 1 μF and 100 nF close to the SUPPLY pin, and C2 of 10 nF close to the OUT pin. A larger capacitor for C1 or C2 is helpful for EMC and ESD; however, it takes a longer time to charge up the capacitor and could affect PWM dimming performance.

Current setting by the sense resistor is as described in Equation 1.

Equation 4. TPS92612-Q1 eq9.gif

LED-string maximum forward voltage = 3 × 2.5 V = 7.5 V.

Parallel resistor R(P) is recommended to consume 1/2 of the total current at maximum supply voltage.

Equation 5. TPS92612-Q1 eq-6.gif

Total device power consumption is maximum with 16-V input and LEDs at minimal forward voltage.

Equation 6. TPS92612-Q1 eq-7.gif

Resistor R(P) maximum power consumption is at 16-V input.

Equation 7. TPS92612-Q1 eq-8.gif