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PDF LM6588MT Data sheet ( Hoja de datos )
| Número de pieza | LM6588MT | |
| Descripción | TFT-LCD Quad/ 16V RRIO High Output Current Operational Amplifier | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LM6588MT (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
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May 2003
LM6588
TFT-LCD Quad, 16V RRIO High Output Current
Operational Amplifier
General Description
The LM6588 is a low power, high voltage, rail-to-rail input-
output amplifier ideally suited for LCD panel VCOM driver and
gamma buffer applications. The LM6588 contains four unity
gain stable amplifiers in one package. It provides a common
mode input ability of 0.5V beyond the supply rails, as well as
an output voltage range that extends to within 50mV of either
supply rail. With these capabilities, the LM6588 provides
maximum dynamic range at any supply voltage. Operating
on supplies ranging from 5V to 16V, while consuming only
750µA per amplifier, the LM6588 has a bandwidth of 24MHz
(−3dB).
The LM6588 also features fast slewing and settling times,
along with a high continuous output capability of 75mA. This
output stage is capable of delivering approximately 200mA
peak currents in order to charge or discharge capacitive
loads. These features are ideal for use in TFT-LCDs.
The LM6588 is available in the industry standard 14-pin SO
package and in the space-saving 14-pin TSSOP package.
The amplifiers are specified for operation over the full −40˚C
to +85˚C temperature range.
Features
(VS = 5V, TA = 25˚C typical values unless specified)
n Input common mode voltage
0.5V beyond rails
n Output voltage swing (RL = 2kΩ)
n Output short circuit current
50mV from rails
±200mA
n Continuous output current
75mA
n Supply current (per amp, no load)
750µA
n Supply voltage range
5V to 16V
n Unity gain stable
n −3dB bandwidth (AV = +1)
n Slew rate
24MHz
11V/µSec
n Settling time
270ns
n SO-14 and TSSOP-14 package
n Manufactured in National Semiconductor’s
state-of-the-art bonded wafer, trench isolated
complementary bipolar VIP10™ technology for high
performance at low power levels
Applications
n LCD panel VCOM driver
n LCD panel gamma buffer
n LCD panel repair amp
Test Circuit Diagram
© 2003 National Semiconductor Corporation DS200734
20073401
www.national.com
1 page  
Typical Performance Characteristics Unless otherwise specified, all limits guaranteed for TJ = 25˚C,
VCM = 1/2VS and RL = 2kΩ.
Gain Phase vs. Temperature (VS = 5V)
Gain Phase vs. Temperature (VS = 16V)
20073403
Gain Phase vs. Capacitive Loading (VS = 5V)
20073404
Gain Phase vs. Capacitive Loading (VS = 16V)
PSRR (VS = 5V)
20073405
PSRR (VS = 16V)
20073406
20073407
5
20073408
www.national.com
5 Page 
TFT Display Application (Continued)
light filter that modulates light transmitted from the back to
the front of a display. A pixel’s bottom plate lies on the
backside of a display where a light source is applied, and the
top plate lies on the front, facing the viewer. On a Twisted
Neumatic (TN) display, which is typical of most TFT displays,
a pixel transmits the greatest amount of light when VPIXEL is
less ±0.5V, and it becomes less transparent as this voltage
increases with either a positive or negative polarity. In short,
an LCD pixel can be thought of as a capacitor, through
which, a controlled amount of light is transmitted by varying
VPIXEL.
20073426
FIGURE 1. Individual LCD Pixel
the Column Drivers supply this voltage via the column lines.
Column Drivers ‘write’ this voltage to the pixels one row at a
time, and this is accomplished by having the Row Drivers
select an individual row of pixels when their voltage levels
are transmitted by the Column Drivers. The Row Drivers
sequentially apply a large positive pulse (typically 25V to
35V) to each row line. This turns-on NMOS transistors con-
nected to an individual row, allowing voltages from the col-
umn lines to be transmitted to the pixels.
VCOM DRIVER
The VCOM driver supplies a common voltage (VCOM) to all
the pixels in a TFT panel. VCOM is a constant DC voltage that
lies in the middle of the column drivers’ output voltage range.
As a result, when the column drivers write to a row of pixels,
they apply voltages that are either positive or negative with
respect to VCOM. In fact, the polarity of a pixel is reversed
each time its row is selected. This allows the column drivers
to apply an alternating voltage to the pixels rather than a DC
signal, which can ‘burn’ a pattern into an LCD display.
When column drivers write to the pixels, current pulses are
injected onto the VCOM line. These pulses result from charg-
ing stray capacitance between VCOM and the column lines
(see Figure 2), which ranges typically from 16pF to 33pF per
column. Pixel capacitance contributes very little to these
pulses because only one pixel at a time is connected to a
column, and the capacitance of a single pixel is on the order
of only 0.5pF. Each column line has a significant amount of
series resistance (typically 2kΩ to 40kΩ), so the stray ca-
pacitance is distributed along the entire length of a column.
This can be modeled by the multi-segment RC network
shown in Figure 3. The total capacitance between VCOM and
the column lines can range from 25nF to 100nF, and charg-
ing this capacitance can result in positive or negative current
pulses of 100mA, or more. In addition, a similar distributed
capacitance of approximately the same value exists be-
tween VCOM and the row lines. Therefore, the VCOM driver’s
load is the sum of these distributed RC networks with a total
capacitance of 50nF to 200nF, and this load can modeled
like the circuit in Figure 3.
20073428
20073427
FIGURE 2. TFT Display
Figure 2 is a simplified block diagram of a TFT display,
showing how individual pixels are connected to the row,
column, and VCOM lines. Each pixel is represented by ca-
pacitor with an NMOS transistor connected to its top plate.
Pixels in a TFT panel are arranged in rows and columns.
Row lines are connected to the NMOS gates, and column
lines to the NMOS sources. The back plate of every pixel is
connected to a common voltage called VCOM. Pixel bright-
ness is controlled by voltage applied to the top plates, and
FIGURE 3. Model of Impedance between VCOM and
Column Lines
A VCOM driver is essentially a voltage regulator that can
source and sink current into a large capacitive load. To
simplify the analysis of this driver, the distributed RC network
of Figure 3 has been reduced to a single RC load in Figure
4. This load places a large capacitance on the VCOM driver
output, resulting in an additional pole in the op amp’s feed-
back loop. However, the op amp remains stable because
CLOAD and RESR create a zero that cancels the effect of this
pole. The range of CLOAD is 50nF to 200nF and RESR is 20Ω
to 100Ω, so this zero will have a frequency in the range of
11 www.national.com
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LM6588MT.PDF ] | |
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