BUF16821 Datasheet, PDF (19/29 Pages) EPCOS – Programmable Gamma-Voltage Generator and VCOM Calibrator with Integrated Two-Bank Memory

BUF16821
www.ti.com ...................................................................................................................................................................................................... SBOS428 – JULY 2008
END-USER SELECTED GAMMA CONTROL
Because the BUF16821 has two banks of nonvolatile
memory, it is well-suited for providing two levels of
gamma control by using the BKSEL pin, as shown in
Figure 17. When the state of the BKSEL pin changes,
the BUF16821 updates all 18 programmable buffer
outputs simultaneously after 750µs (±80µs).
To update all 18 programmable output voltages
simultaneously via hardware, toggle the BKSEL pin to
switch between Gamma Curve 0 (stored in Bank0)
and Gamma Curve 1 (stored in Bank1).
All DAC/V_COM registers and output voltages are
updated simultaneously after approximately 750µs.
5V
BKSEL
BUF16821
Switch
OUT1
Change in
Output Voltages
OUT16
I²C
DYNAMIC GAMMA CONTROL
Dynamic gamma control is a technique used to
improve the picture quality in LCD television
applications. This technique typically requires
switching gamma curves between frames. Using the
BKSEL pin to switch between two gamma curves
does not often provide good results because of the
750µs required to transfer the data from the
nonvolatile memory to the DAC register. However,
dynamic gamma control can still be accomplished by
storing two gamma curves in an external EEPROM
and writing directly to the DAC register (volatile).
The double register input structure saves
programming time by allowing updated DAC values to
be pre-stored 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/V_COM output values
remain unchanged—the display is unaffected. At the
beginning or the end of a picture frame, the
DAC/V_COM outputs (and therefore, the gamma
voltages) can be quickly updated by writing a '1' in bit
15 of any DAC/V_COM register. For details on the
operation of the double register input structure, see
the Updating the DAC Outputs section.
To update all 18 programmable output voltages
simultaneously via software, perform the following
actions:
STEP 1: Write to registers 1–18 with bit 15 always '0'.
STEP 2: Write any DAC/V_COM register a second time
with identical data. Make sure that bit 15 is set to '1'.
All DAC/V_COM channels are updated simultaneously
after receiving the last bit of data.
Figure 17. Gamma Control
Copyright © 2008, Texas Instruments Incorporated
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