SNVSC36A December   2021  – September 2024 LP5866

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison
  6. 5 Pin Configuration and Functions
  7. 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.     14
    8. 6.7 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Time-Multiplexing Matrix
      2. 7.3.2 Analog Dimming (Current Gain Control)
      3. 7.3.3 PWM Dimming
      4. 7.3.4 ON and OFF Control
      5. 7.3.5 Data Refresh Mode
      6. 7.3.6 Full Addressable SRAM
      7. 7.3.7 Protections and Diagnostics
    4. 7.4 Device Functional Modes
    5. 7.5 Programming
    6. 7.6 Register Maps
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Application
      2. 8.2.2 Design Requirements
      3. 8.2.3 Detailed Design Procedure
        1. 8.2.3.1 Program Procedure
      4. 8.2.4 Application Performance Plots
    3. 8.3 Power Supply Recommendations
      1. 8.3.1 Power Supply Recommendations
      2. 8.3.2 Power Supply Recommendations
      3. 8.3.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Receiving Notification of Documentation Updates
    2. 9.2 Support Resources
    3. 9.3 Trademarks
    4. 9.4 Electrostatic Discharge Caution
    5. 9.5 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

7.3.3 PWM Dimming

There are several methods to control the PWM duty cycle of each LED dot.

  • Individual 8-bit / 16-bit PWM for Each LED Dot

    Every LED has an individual 8-bit or 16-bit PWM register that is used to change the LED brightness by PWM duty. The LP5866 uses an enhanced spectrum PWM (ES-PWM) algorithm to achieve 16-bit depth with high refresh rate, which can avoid flicker under a high speed camera. Comparing with conventional 8-bit PWM, 16-bit PWM can help to achieve ultimate high dimming resolution in LED animation applications.

  • 3 Programmable Groups of 8-bit PWM Dimming

    The group PWM Control is used to select LEDs into 1 to 3 groups where each group has a separate register for duty cycle control. Every LED has 2-bit selection in LED_DOT_GROUP Registers (x = 0, 1, … , 29.) to select whether it belongs to one of the three groups or not:

    • 00: not a member of any group
    • 01: member of group 1
    • 10: member of group 2
    • 11: member of group 3

  • 8-bit PWM for Global Dimming

    The Global PWM Control function affects all LEDs simultaneously.

The final PWM duty cycle can be calculated as below:

Equation 5. PWM_Final(8 bit) = PWM_Individual(8 bit) × PWM_Group(8 bit) × PWM_ Global(8-bit)
Equation 6. PWM_Final(16 bit) = PWM_Individual(16 bit) × PWM_Group(8 bit) × PWM_ Global(8-bit)

The LP5866 supports 125-kHz or 62.5-kHz PWM output frequency. The PWM frequency is selected by configuring the 'PWM_Fre' in Dev_initial register. An internal 31.2-MHz oscillator is used for generating PWM outputs. The high-accuracy design of the oscillator (ƒOSC_ERR ≤ ± 2%) enables a better synchronization if multiple LP5866 devices are connected together.

A PWM phase-shifting scheme is implemented in each current sink to avoid the current overshot when turning on simultaneously. As the LED drivers are not activated simultaneously, the peak load current from the pre-stage power supply is significantly decreased. This scheme also reduces input-current ripple and ceramic-capacitor audible ringing. LED drivers are grouped into three different phases. By configuring the 'PWM_Phase_Shift' in Dev_config1 register, which is default off, the LP5866 supports tphase_shift = 125-ns shifting time shown in Figure 7-4.

  • Phase 1: CS0, CS3, CS6, CS9, CS12, CS15.
  • Phase 2: CS1, CS4, CS7, CS10, CS13, CS16.
  • Phase 3: CS2, CS5, CS8, CS11, CS14, CS17.
LP5866 Phase ShiftFigure 7-4 Phase Shift

To avoid high current sinks output ripple during line switching, current sinks can be configured to turn on with 1 clock delay (62.5 ns or 31.25 ns according to the PWM frequency) after lines turn on, as shown in Figure 7-3. This function can be configured by 'CS_ON_Shift' in Dev_config1 register.

The LP5866 allows users to configure the dimming scale either exponentially (Gamma Correction) or linearly through the 'PWM_Scale_Mode' in Dev_config1 register. If a human-eye-friendly dimming curve is desired, using the internal fixed exponential scale is an easy approach. If a special dimming curve is desired, TI recommends using the linear scale with software correction. The LP5866 supports both linear and exponential dimming curves under 8-bit and 16-bit PWM depth. Figure 7-5 is an example of 8-bit PWM depth.

LP5866 Linear and Exponential Dimming CurvesFigure 7-5 Linear and Exponential Dimming Curves

In summary, Figure 7-6 illustrates the PWM control method:

LP5866 PWM Control SchemeFigure 7-6 PWM Control Scheme