SLVS893F December   2008  – May 2019 TPS61500

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Application Circuit
  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 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 Switching Frequency
      2. 7.3.2 Soft Start
      3. 7.3.3 Enable and Thermal Shutdown
      4. 7.3.4 Undervoltage Lockout (UVLO)
      5. 7.3.5 Overvoltage Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 PWM Dimming Method
      2. 7.4.2 Analog Dimming Method
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Analog Dimming Method
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Programming the Overvoltage Protection
          2. 8.2.1.2.2 Programming the LED Current
          3. 8.2.1.2.3 Implementing Dimming
          4. 8.2.1.2.4 Computing the Maximum Output Current
          5. 8.2.1.2.5 Selecting the Inductor
          6. 8.2.1.2.6 Selecting the Schottky Diode
          7. 8.2.1.2.7 Selecting the Compensation Capacitor and Resistor
          8. 8.2.1.2.8 Selecting the Input and Output Capacitor
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Pure PWM Dimming Method
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
        3. 8.2.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Thermal Considerations
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
      2. 11.1.2 Receiving Notification of Documentation Updates
      3. 11.1.3 Community Resources
    2. 11.2 Trademarks
    3. 11.3 Electrostatic Discharge Caution
    4. 11.4 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7.4.2 Analog Dimming Method

When capacitor C5 is connected to the DIMC pin, the FB regulation voltage is scaled proportional to the external PWM signal's duty cycle; therefore, it achieves LED brightness change, shown in Figure 7. The relationship between the duty cycle and LED current is given by Equation 1:

Equation 1. TPS61500 eq_iled2_lvs893.gif

where

  • Duty is the duty cycle of the PWM signal.

The device chops up the internal 200-mV reference voltage at the duty cycle of the PWM signal. The pulsed reference voltage is then filtered by a low pass filter that is composed of an internal 25-kΩ resistor and the external capacitor C5. The output of the filter is connected to the error amplifier as the reference voltage for the FB pin. Therefore, although a PWM signal is used for brightness dimming, only the LED DC current is modulated. This eliminates the audible noise that often occurs when the LED current is pulsed during PWM dimming. Unlike other methods for filtering the PWM signal, the device analog dimming method is independent of the PWM logic voltage level which often has large variations.

For optimum performance, TI recommends that the value of C5 be as large as possible to provide adequate filtering for the PWM frequency. For example, when the PWM frequency is 5-kHz, C5 equal to 1 μF is sufficient. The recommended minimum PWM on time at start-up is 200 µs. After start-up, TI recommends a minimum PWM duty cycle of 1%.