BUF16821-Q1 Datasheet, PDF (19/38 Pages) Texas Instruments – Programmable Gamma-Voltage Generator

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BUF16821-Q1
SBOS712 – MAY 2014
7.4 Device Functional Modes
7.4.1 End-User Selected Gamma Control
The device is well-suited for providing two levels of gamma control by using the BKSEL pin because the device
has two banks of nonvolatile memory, as shown in Figure 18. When the state of the BKSEL pin changes, the
device updates all 18 programmable buffer outputs simultaneously after 750 μs (±80 μs).
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 and VCOM registers and output voltages are updated simultaneously after approximately 750 μs.
5V
BKSEL
Device
Switch
OUT1
Change in
Output Voltages
OUT16
I²C
Figure 18. Gamma Control
7.4.2 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 750 μs 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 electrically erasable programmable read-only memory (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 and VCOM output values remain unchanged—the
display is unaffected. At the beginning or the end of a picture frame, the DAC and VCOM outputs (and therefore,
the gamma voltages) can be quickly updated by writing a 1 in bit 15 of any DAC and VCOM register. For details
on the operation of the double register input structure, see the Updating the DAC Output Voltages 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 and VCOM register a second time with identical data. Make sure that bit 15 is set to 1.
All DAC and VCOM channels are updated simultaneously after receiving the last bit of data.
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