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

8.3.1 Time-Multiplexing Matrix

The LP5868 device uses time-multiplexing matrix scheme to support up to 144 LED dots with a single chip. The device integrates 18 current sinks with 8 scan lines to drive 18 × 8 = 144 LED dots or 6 × 8 = 48 RGB pixels. In matrix control scheme, the device scans from Line 0 to Line 7 sequentially as shown in Figure 8-1. Current gain and PWM duty registers are programmable for each LED dot to support individual analog and PWM dimming.

Figure 8-1 Scan Line Control Scheme

There are 8 high-side p-channel MOSFETs (PMOS) integrated in LP5868 device. Users can flexibly set the active scan numbers from 1 to 8 by configuring the 'Max_Line_Num' in Dev_initial register. The time-multiplexing matrix timing sequence follows the Figure 8-2.

Figure 8-2 Time-Multiplexing Matrix Timing Sequence

One cycle time of the line switching can be calculated as below:

Equation 1. tline_switch = tPWM + tSW_BLK + 2 × tphase_shift
  • tPWM is the current sink active time, which equals to 8 us (PWM frequency set at 125 kHz) or 16 us (PWM frequency set at 62.5 kHz) by configuring 'PWM_Fre' in Dev_initial register.
  • tSW_BLK is the switch blank time, which equals to 1 us or 0.5 us by configuring 'SW_BLK' in Dev_config1 register.
  • tphase_shift is the PWM phase shift time, which equal to 0 or 125 ns by configuring 'PWM_Phase_Shift' in Dev_config1 register.

Total display time for one complete sub-period is tsub_period and it can be calculated by the following equation:

Equation 2. tsub_period = tline_switch × Scan_line#
  • Scan_line# is the scan line number determined by 'Max_Line_Num' in Dev_initial register.

The time-multiplexing matrix scheme time diagram is shown in Figure 8-3. The tCS_ON_Shift is the current sink turning on shift by configuring 'CS_ON_Shift' bit in Dev_config1 register.

Figure 8-3 Time-Multiplexing Matrix Timing Diagram

The LP5868 device implements deghosting and low brightness compensation to remove the side effects of matrix topology:

  • Deghosting: Both upside deghosting and downside deghosting are implemented to eliminate the LED's unexpected weak turn-on.
    • Upside_deghosting: discharge each scan line during its off state. By configuring the 'Up_Deghost' in Dev_config3 register, the LP5868 discharges and clamp the scan line switch to a certain voltage.
    • Downside_deghosting: pre-charge each current sink voltage during its OFF state. The deghosting capability can be adjusted through the 'Down_Deghost' in Dev_config3 register.

  • Low Brightness Compensation: 3 groups compensation are implemented to overcome the color-shift and non-uniformity in low brightness conditions. The compensation capability can be through 'Comp_Group1', 'Comp_Group2', and 'Comp_Group3' in Dev_config2 register.
    • Compensation_group 1: CS0, CS3, CS6, CS9, CS12, CS15.
    • Compensation_group 2: CS1, CS4, CS7, CS10, CS13, CS16.
    • Compensation_group 3: CS2, CS5, CS8, CS11, CS14, CS17.