SNVSC32 December   2021 LP5868

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison
  6. 6 Pin Configuration and 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 Timing Requirements
    7. 7.7 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Time-Multiplexing Matrix
      2. 8.3.2 Analog Dimming (Current Gain Control)
      3. 8.3.3 PWM Dimming
      4. 8.3.4 ON and OFF Control
      5. 8.3.5 Data Refresh Mode
      6. 8.3.6 Full Addressable SRAM
      7. 8.3.7 Protections and Diagnostics
    4. 8.4 Device Functional Modes
    5. 8.5 Programming
    6. 8.6 Register Maps
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Application
      2. 9.2.2 Design Requirements
      3. 9.2.3 Detailed Design Procedure
      4. 9.2.4 Program Procedure
      5. 9.2.5 Application Performance Plots
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Receiving Notification of Documentation Updates
    2. 12.2 Support Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

8.3.3 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 LP5868 uses an enhanced spectrum PWM (ES-PWM) algorithm to achieve 16-bit depth with high refresh rate and this can avoid flicker under 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, … , 54.) 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 LP5868 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 oscillator’s high accuracy design (ƒOSC_ERR ≤ ± 2%) enables a better synchronization if multiple LP5868 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 LP5868 supports tphase_shift = 125-ns shifting time shown in Figure 8-4.

  • Phase 1: CS0, CS3, CS6, CS9, CS12, CS15.
  • Phase 2: CS1, CS4, CS7, CS10, CS13, CS16.
  • Phase 3: CS2, CS5, CS8, CS11, CS14, CS17.
Figure 8-4 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 8-3. This function can be configured by 'CS_ON_Shift' in Dev_config1 register.

The LP5868 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 LP5868 supports both linear and exponential dimming curves under 8-bit and 16-bit PWM depth. Figure 8-5 is an example of 8-bit PWM depth.

Figure 8-5 Linear and Exponential Dimming Curves

In summary, the PWM control method is illustrated as Figure 8-6:

Figure 8-6 PWM Control Scheme