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ADD8704 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADD8704
Beschreibung 16 V Quad Operational Amplifier
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 16 Seiten
ADD8704 Datasheet, Funktion
FEATURES
Single-supply operation: 4.5 V to 16.5 V
Upper/lower buffers swing to VDD/GND
Continuous output current: 35 mA
VCOM peak output current: 250 mA
Offset voltage: 15 mV
Slew rate: 6 V/µs
Unity gain stable with large capacitive loads
Supply current: 700 µA per amplifier
Drop-in replacement for EL5420
APPLICATIONS
TFT LCD monitor panels
TFT LCD notebook panels
Communications equipment
Portable instrumentation
Electronic games
GENERAL DESCRIPTION
The ADD8704 is a single-supply quad operational amplifier that
has been optimized for today’s low cost TFT LCD notebook and
monitor panels. Output channels A and D swing to the rail for
use as end-point gamma references. Output channels B and C
provide high continuous and peak current drive for use as VCOM
or repair amplifiers; they can also be used as midpoint gamma
references. All four amplifiers have excellent transient response
and have high slew rate and capacitive load drive capability. The
ADD8704 is specified over the –40°C to +85°C temperature
range and is available in either a 14-lead TSSOP or a 16-lead
LFCSP package for thin, portable applications.
Table 1. Input/Output Characteristics
Channel VIH
VIL
A VDD – 1.7 V GND
B VDD – 1.7 V GND
C VDD GND
D VDD GND + 1.7 V
IO (mA)
15
35
35
15
ISC (mA)
150
250
250
150
16 V Quad
Operational Amplifier
ADD8704
PIN CONFIGURATIONS
OUT A 1
–IN A 2
–+
14 OUT D
+–
13 –IN D
+IN A 3
12 +IN D
V+ 4 ADD8704 11 V–
+IN B 5
10 +IN C
–IN B 6
OUT B 7
–+
9 –IN C
+–
8 OUT C
Figure 1. 14-Lead TSSOP (RU Suffix)
–IN A 1
+IN A 2
V+ 3
+IN B 4
ADD8704
TOP VIEW
12 –IN D
11 +IN D
10 V–
9 +IN C
Figure 2. 16-Lead CSP (CP Suffix)
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.326.8703 © 2003 Analog Devices, Inc. All rights reserved.






ADD8704 Datasheet, Funktion
ADD8704
TYPICAL PERFORMANCE CHARACTERISTICS
600
VS = 16V
500
400
300
200
100
0
–9 –7 –5 –3 –1 1 3 5 7
INPUT OFFSET VOLTAGE (mV)
9 11
Figure 3. Input Offset Voltage, VS = 16 V
20
VS = 16V
18
16
14
12
10
8
6
4
2
0
0
10 20 30 40 50 60 70 80 90 100
TCVOS (µV/°C)
Figure 4. Input Offset Voltage Drift, VS = 16 V
10
8
VS = 16V
VCM = VS/2
6
4
2
0
–2
A
D
B
C
–4
–6
–8
–10
–60 –40 –20
0
20 40 60 80 100
TEMPERATURE (°C)
Figure 5. Input Bias Current vs. Temperature
10
VS = 16V
8
6
4C
2
0B
–2 A
–4 D
–6
–8
–10
0 2 4 6 8 10 12 14 16
COMMON-MODE VOLTAGE (V)
Figure 6. Offset Voltage vs. Common-Mode Voltage
400
A VS = 16V
200
0
–200
–400
–600
D
B
C
–800
–1000
–60 –40 –20
0
20 40 60
TEMPERATURE (°C)
80
Figure 7. Input Bias Current vs. Temperature
80
VS = 16V
60
40
20
D
0
C
B
–20
–40
A
–60
–80
–60
–40 –20 0 20 40
TEMPERATURE (°C)
60
80
Figure 8. Input Offset Current vs. Temperature
100
100
Rev. 0 | Page 6 of 16

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ADD8704 pdf, datenblatt
ADD8704
APPLICATION INFORMATION
THEORY
The ADD8704 is designed for use in LCD gamma correction
circuits. Depending on the panel architecture, between 4 and 18
different gamma voltages may be needed. These gamma
voltages provide the reference voltages for the column driver
RDACs. Due to the capacitive nature of LCD panels, it is
necessary for these drivers to provide high capacitive load drive.
In addition to providing gamma reference voltages, these parts
are also capable of providing the VCOM voltage. VCOM is the
center voltage common to all the LCD pixels. Since the VCOM
circuit is common to all the pixels in the panel, the VCOM driver
is designed to supply continuous currents up to 35 mA.
INPUT
The ADD8704 has four amplifiers specifically designed for the
needs of an LCD panel. Figure 36 shows a typical gamma
correction curve for a normally white twisted nematic LCD
panel. The symmetric curve comes from the need to reverse the
polarity on the LC pixels to avoid “burning” in the image. The
application therefore requires gamma voltages that come close
to both supply rails. To accommodate this transfer function, the
ADD8704 has been designed to have four different amplifiers in
one package.
VDD
VG1
VG2
VG3
VG4
VG5
VG6
VG7
VG8
VG9
VG10
VSS
0
16 32
48
GRAY SCALE BITS
Figure 36. LCD Gamma Correction Curve
64
Amplifier A has a single-supply PNP input stage followed by a
folded cascode stage. This provides an input range that goes to
the bottom rail. This amplifier can therefore be used to provide
the bottom voltage on the RDAC string.
Amplifier B (PNP folded cascode) swings to the low rail as well,
but it provides 35 mA continuous output current versus 15 mA.
This buffer is suitable for lower RDAC range, middle RDAC
range, or VCOM applications.
Amplifier C is a rail-to-rail input range that makes the
ADD8704 suitable for use anywhere on the RDAC as well as for
VCOM applications.
Amplifier D has an NPN follower input stage. This covers the
upper rail to GND plus 1.7 V. This amplifier is suitable for the
upper range of the RDAC.
OUTPUT
The outputs of the amplifiers have been designed to match the
performance needs of the gamma correction circuit. All four of
the amplifiers have rail-to-rail outputs, but the current drive
capabilities differ. Since amplifier A is suited for voltages close
to VSS (GND), the output is designed to sink more current than
it sources; it can sink 15 mA of continuous current. Likewise,
since amplifier D is primarily used for voltages close to VDD, it
sources more current. Amplifier D can source 15 mA of
continuous current. Amplifiers B and C are designed for use as
either midrange gamma or VCOM amplifiers. They therefore sink
and source equal amounts of current. Since they are used as
VCOM amplifiers, they have a drive capability of up to 35 mA of
continuous current.
The nature of LCD panels introduces a large amount of
parasitic capacitance from the column drivers as well as the
capacitance associated with the liquid crystals via the common
plane. This makes capacitive drive capability an important
factor when designing the gamma correction circuit.
IMPORTANT NOTE
Because of the asymmetric nature of amplifiers A and D, care
must be taken to connect an input that forces the amplifiers to
operate in their most productive output states. Amplifier D has
very limited sink capabilities, while amplifier A does not source
well. If more than one ADD8704 is used, set the amplifier D
input to enable the amplifier output to source current and set
the amplifier A input to force a sinking output current. This
means making sure the input is above the midpoint of the
common-mode input range for amplifier D and below the
midpoint for amplifier A. Mathematically speaking, make sure
VIN > VS/2 for amplifier D and VIN < VS/2 for amplifier A.
Figure 37 shows an example using 4 ADD8704s to generate 10
gamma outputs. Note that the top three resistor tap-points are
connected to the amplifier D inputs, thus assuring these
channels will source current. Likewise, the bottom three resistor
tap-points are connected to the amplifier A inputs to provide
sinking output currents.
Rev. 0 | Page 12 of 16

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