SBOS571C August   2011  – August 2018 BUF20800-Q1

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      Simplified Block Diagram
  4. Revision History
  5. Pin Configuration and Functions
    1.     Pin Functions
  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. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 General-call Reset and Power-up
      2. 7.3.2 Output Voltage
      3. 7.3.3 Output Latch
      4. 7.3.4 Programmable VCOM
      5. 7.3.5 REFH and REFL Input range
    4. 7.4 Device Functional Modes
      1. 7.4.1 Replacement of Traditional Gamma Buffer
      2. 7.4.2 Dynamic Gamma Control
    5. 7.5 Programming
      1. 7.5.1 Two-wire Bus Overview
      2. 7.5.2 Data Rates
      3. 7.5.3 Read/Write Operations
        1. 7.5.3.1 Writing
        2. 7.5.3.2 Reading
      4. 7.5.4 Register Maps
        1. 7.5.4.1 Addressing the BUF20800-Q1
      5. 7.5.5 Registers
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Input Capacitor Selection
        2. 8.2.2.2 REFH and REFL Voltage Settings
      3. 8.2.3 Application Curves
      4. 8.2.4 Configuration for 20 Gamma Channels
      5. 8.2.5 Configuration for 22 Gamma Channels
      6. 8.2.6 The BUF20800-Q1 in Industrial Applications
      7. 8.2.7 Total TI Panel Solution
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 General PowerPAD Design Considerations
    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

Package Options

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

Dynamic Gamma Control

Dynamic gamma control is a technique used to improve the picture quality in LCD TV applications. The brightness in each picture frame is analyzed and the gamma curves are adjusted on a frame-by-frame basis. The gamma curves are typically updated during the short vertical blanking period in the video signal. Figure 11 shows a block diagram using the BUF20800-Q1 for dynamic gamma control and VCOM output.

The BUF20800-Q1 is ideally suited for rapidly changing the gamma curves because of its unique topology:

  • double register input structure to the DAC;
  • fast serial interface;
  • simultaneous updating of all DACs by software. See the Read/Write Operations to write to all registers and the Output Latch sections.

The double register input structure saves programming time by allowing updated DAC values to be pre-loaded into the first register bank. Storage of this data can occur while a picture is still being displayed. Because the data are only stored into the first register bank, the DAC output values remain unchanged—the display is unaffected. During the vertical sync period, the DAC outputs (and therefore, the gamma voltages) can be quickly updated either by using an additional control line connected to the LD pin, or through software—writing a ‘1’ in bit 15 of any DAC register. For the details on the operation of the double register input structure, see the Output Latch section.

Example: Update all 18 gamma registers simultaneously via software.

Step 1: Check if LD pin is placed in HIGH state.

Step 2: Write DAC Registers 1−18 with bit 15 always ‘0’.

Step 3: Write any DAC register a second time with identical data. Make sure that bit 15 is ‘1’. All DAC channels will be updated simultaneously after receiving the last bit of data. (Note: this step may be eliminated by setting bit 15 of DAC 18 to ‘1’ in the previous step.)

BUF20800-Q1 appinfo_dyngamma_SBOS571.gifFigure 11. Dynamic Gamma Control