ADD8701ACP-REEL7 Analog Devices Inc, ADD8701ACP-REEL7 Datasheet - Page 7

• Manufacturer Part Number: ADD8701ACP-REEL7
• Manufacturer: Analog Devices Inc

Specifications of ADD8701ACP-REEL7

• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 32
• Lead Free Status / RoHS Status: Not Compliant

APPLICATIONS
LCD Gamma Reference Buffers
In high resolution TFT-LCD displays, gamma correction must
be performed to correct the nonlinearity in the LCD panel’s
transmission characteristics. A typical TFT-LCD panel consisting
of 256 grayscale levels takes an 8-bit digital word to select an
appropriate gamma reference voltage. An 8-bit source driver may
use 12 analog voltages that match the characteristic gamma curve
for optimum panel picture quality. The ADD8701 is specifically
designed to generate analog reference voltages to meet the gamma
characteristics of an LCD panel used by the source driver. The
gamma reference buffers offer 10 mA drive capability.
The ADD8701 is designed to meet the rail-to-rail capability
needed by the application and yet offers a low cost-per-channel
solution. The design maximizes the die area by offering channels
to swing to the positive and negative rails. It is imperative that
the channels swinging close to the supply rail be used for the
positive gamma references and that the channels swinging close
to GND be used for the negative gamma references. See Figure 2
for an example of the application circuit.
LCD VCOM Buffer
The output of the VCOM buffer is designed to control the voltage
on the back plate of the LCD display. The buffer must be capable
of sinking and sourcing capacitive pulse current. The amplifier
stability is designed for high load capacitance. A high quality
ceramic capacitor is recommended to supply short duration current
pulses at the output. The VCOM buffer of the ADD8701 can
handle up to 35 mA of continuous output current and can drive
up to 1,000 nF of pure capacitive load.
Unused Buffers
Inputs of any unused buffer should be tied to the ground plane.
REV. 0
–10
70
60
50
40
30
20
10
0
0
TPC 28. Voltage Noise Density
vs. Frequency
V
VCOM AND BUFFERS 1 TO 9
MARKER SET @ 10kHz
MARKER READING = 25.7nV/ Hz
DD
= 16V
5
FREQUENCY – Hz
10
15
20
25
–10
70
60
50
40
30
20
10
0
0
TPC 29. Voltage Noise Density
vs. Frequency
V
BUFFERS 10 TO 12
MARKER SET @ 10kHz
MARKER READING = 36.6nV/ Hz
DD
= 16V
5
FREQUENCY – Hz
10
–7–
15
20
ADD8701
A12
A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
25
Figure 2. Application Circuit
LCD SOURCE DRIVER
GMA
GMA
GMA
GMA
GMA
GMA
GMA
GMA
GMA
GMA
GMA
GMA
ADD8701