ADD8707WCPZ-REEL7 Analog Devices Inc, ADD8707WCPZ-REEL7 Datasheet - Page 12

• Manufacturer Part Number: ADD8707WCPZ-REEL7
• Description: IC GAMMA BUFFER 12CHAN 48LFCSP
• Manufacturer: Analog Devices Inc

Specifications of ADD8707WCPZ-REEL7

• Applications: TFT-LCD Panels: Gamma Buffer, VCOM Driver
• Number Of Circuits: 12
• -3db Bandwidth: 4.5MHz
• Slew Rate: 6 V/µs
• Current - Supply: 8.3mA
• Current - Output / Channel: 15mA
• Voltage - Supply, Single/dual (±): 7.5 V ~ 16 V
• Mounting Type: Surface Mount
• Package / Case: 48-VFQFN, CSP Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADD8707
APPLICATION NOTES
The ADD8707 is a mask-programmable gamma reference
generator that allows source drivers to be optimized for the
different combinations of liquid crystals, glass sizes, etc. in
large LCD panels. It generates 12 gamma reference outputs
that can be mask-programmed in 0.2% increments using the
500 matched internal resistors (Figure 23), so that every point
on the curve can be targeted within 0.1% of the desired value.
In a typical panel application, the selected source drivers have
an internal gamma curve that is not ideal for the specific panel
(Figure 24). The ADD8707 allows the gamma curve in the
source drivers to be adjusted appropriately, and also insures that
all the source drivers have the same gamma curve.
16
14
12
10
8
6
4
2
0
Figure 23. 500 Mask-Programmable Resistor String
CORRECTED BY ADD8707
Figure 24. Original and Corrected Gamma Curves
TAP POINT 4
TAP POINT 3
TAP POINT 2
TAP POINT 1
PANEL GAMMA CURVE
GAMMA REFERENCE INPUT POINTS
EACH R = 30Ω
TYPICALLY
ORIGINAL GAMMA CURVE
IN SOURCE DRIVERS
TAP POINT 500
TAP POINT 499
TAP POINT 498
TAP POINT 497
Rev. A | Page 12 of 20
The matching and tracking accuracy of the internal resistors is
typically 0.1% with worst-case deviation from the desired curve
within 0.4% of the ideal gamma curve, over temperature.
The ADD8707 also includes a low dropout linear regulator to
provide a stable reference level for the gamma curve for
optimum panel performance.
TAP POINT SELECTION
The ADD8707 uses a single resistor string consisting of 500
individual elements. The tap points are mask programmable
and completely independent of each other. Refer to the Tap
Point and Regulator Voltage Request Form in this data sheet.
Tap point voltages can be derived from the following equation:
where TP
Table 5. Typical Mask Implementation
V
V
V
V
V
V
V
V
V
V
V
V
V
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
DD
12
11
10
9
8
7
6
5
4
3
2
1
= 16 V, V
V
OUT
X
X
is the desired tap point for the X
=
Tap Point (X)
500
419
365
349
343
297
213
173
163
146
95
7
REG OUT
Figure 25. Gamma Buffers Tap Point Circuit.
TP
500
V
X
IN
X
×
= 14.4 V, 0 ≤ X ≤ 500
V
500–TP
REG
TP
V
OUT
REG OUT
X
X
Voltage
14.400
12.067
10.512
10.051
9.878
8.554
6.134
4.982
4.694
4.205
2.736
0.202
V
OUT
th
X
channel.
Units
V
V
V
V
V
V
V
V
V
V
V
V