BUF01900 Datasheet, PDF (14/25 Pages) Texas Instruments – Programmable Voltage Source with Memory

BUF01900
BUF01901
SBOS337A − OCTOBER 2006 − REVISED OCTOBER 2006
V_COM CALIBRATION
The BUF0190x provides a simple, time- and cost-efficient
means to adjust the flicker performance of LCD panels ei-
ther manually or automatically during the final stages of the
LCD panel manufacturing process.
The 10-bit adjustment resolution of the BUF0190x ex-
ceeds the typical adjustment resolution of existing V_COM
calibrators significantly. As with a traditional V_COM adjust-
ment, which uses a mechanical potentiometer and a volt-
age divider for adjustment (see Figure 21), the BUF0190x
uses an external voltage divider that is used to set the ini-
tial V_COM voltage as well as the adjustment range.
AVDD
R_A
R_B
R_C
V_COM
www.ti.com
(a) Code 00h equivalent circuit.
BUF0190x
V_S
250kΩ
R₁
V_BIAS
R₂
(1)
V_COM
(b) Code 3FFh equivalent circuit.
BUF0190x
V_S
V_S
250kΩ
R₁
V_BIAS
R₂
(1)
V_COM
NOTE: (1) Integrated into BUF01900 or external.
Figure 21. Traditional V_COM Adjustment
As Figure 22 shows, the 10-bit DAC acts as a Rail-to-Rail
output voltage source with a nominal 250kΩ of output im-
pedance. For example, at Code 000h, the lowest V_COM
voltage is achieved since the 250kΩ impedance is now in
parallel with R₂, which lowers the impedance of the lower
side of the voltage divider. Consequently, code 3FFh re-
sults in the highest adjustable V_COM voltage.
Once the desired output level is obtained, the part can
store the final setting using the non-volatile on-chip
memory. See Programming section for detailed informa-
tion.
Figure 22. Simplified Block Diagram for V_COM
Adjustment using BUF0190x
SELECTING THE ADJUSTMENT STEP SIZE
A maximum of 1024 adjustment steps can be realized with
the BUF0190x, leading to very high adjustment resolution
and very small step sizes. This flexibility can be advanta-
geous during the panel development phase. In a practical
production setting, however, this capability might lead to
adjustment times that can be too long. A simple solution is
to increase the step size between settings to more practi-
cal values for mass production. Limiting the number of ad-
justment steps between code 000h and code 3FFh to be-
tween 16 and 128 has been shown to typically yield
acceptable adjustment results in the smallest amount of
adjustment time.
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