BUF20800-Q1 Datasheet, PDF (15/32 Pages) Texas Instruments – 18-CHANNEL GAMMA VOLTAGE GENERATOR WITH TWO PROGRAMMABLE VCOM CHANNELS

BUF20800-Q1
www.ti.com
SBOS571 – AUGUST 2011
REPLACEMENT OF TRADITIONAL GAMMA BUFFER
Traditional gamma buffers rely on a resistor string (often using expensive 0.1% resistors) to set the gamma
voltages. During development, the optimization of these gamma voltages can be time-consuming. Programming
these gamma voltages with the BUF20800-Q1 can significantly reduce the time required for gamma voltage
optimization. The final gamma values can be written into an external EEPROM to replace a traditional gamma
buffer solution. During power-up of the LCD panel, the timing controller reads the EEPROM and loads the values
into the BUF20800-Q1 to generate the desired gamma voltages. Figure 11a shows the traditional resistor string;
Figure 11b shows the more efficient alternative method using the BUF20800-Q1.
BUF20800-Q1 uses the most advanced high-voltage CMOS process available today, which allows it to be
competitive with traditional gamma buffers.
This technique offers significant advantages:
• It shortens development time significantly.
• It allows demonstration of various gamma curves to LCD monitor makers by simply uploading a different set
of gamma values.
• It allows simple adjustment of gamma curves during production to accommodate changes in the panel
manufacturing process or end-customer requirements.
• It decreases cost and space.
a) Traditional
b)BUF20800-Q1 Solution
BUFxx704
PC
SDA
SCL
Timing
Controller
EEPROM
BUF20800-Q1
V_{COM OUT1}
V_{COM OUT2}
V_COM
OUT1
OUT2
OUT17
Gamma
References
OUT18
SDA
SCL
LCD Panel Electronics
Control Interface
Figure 11. Replacement of the Traditional Gamma Buffer
PROGRAMMABLE V_COM
The V_COM channels of the BUF20800-Q1 can swing to 2V from the positive supply rail while sourcing 50 mA and
to 1 V above the negative rail while sinking 50 mA (see Figure 4, typical characteristic Output Voltage vs Output
Current). To store the gamma and the V_COM values, an external EEPROM is required. During power-up of the
LCD panel, the timing controller can then read the EEPROM and load the values into the BUF20800-Q1 to
generate the desired V_COM voltages, as illustrated in Figure 11 and Figure 12. The V_COM channels can be
programmed independently from the gamma channels.
Copyright © 2011, Texas Instruments Incorporated
Product Folder Link(s): BUF20800-Q1
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