SBOS571C August   2011  – August 2018 BUF20800-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Block Diagram
  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 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. 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. 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

7.3.5 REFH and REFL Input range

Best performance and output swing range of the BUF20800-Q1 are achieved by applying REFH and REFL voltages that are slightly below the power-supply voltages. Most specifications have been tested at REFH = Vs − 200mV and REFL = GND + 200mV. The REFH internal buffer is designed to swing very closely to Vs and the REFL internal buffer to GND. However, there is a finite limit on how close they can swing before saturating. To avoid saturation of the internal REFH and REFL buffers, the REFH voltage should not be greater than Vs −100mV and REFL voltage should not be lower than GND + 100mV. Figure 9 shows the swing capability of the REFH and REFL buffers.

The other consideration when trying to maximize the output swing capability of the gamma buffers is the limitation in the swing range of output buffers (OUT1−18, VCOM1, and VCOM2), which depends on the load current. A typical load in the LCD application is 5−10mA. For example, if OUT1 is sourcing 10mA, the swing is typically limited to about Vs − 200mV. The same applies to OUT18, which typically limits at GND + 200mV when sinking 10mA. An increase in output swing can only be achieved for much lighter loads. For example, a 3mA load typically allows the swing to be increased to approximately Vs − 100mV and GND + 100mV.

Connecting REFH directly to Vs and REFL directly to GND does not damage the BUF20800-Q1. As discussed above however, the output stages of the REFH and REFL buffers will saturate. This condition is not desirable and can result in a small error in the measured output voltages of OUT1−18, VCOM1, and VCOM2. As described above, this method of connecting REFH and REL does not help to maximize the output swing capability.

BUF20800-Q1 appinfo_refbuffout_outcurr_bos571.gifFigure 9. Reference Buffer Output Voltage vs Output Current