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PDF LM2403T Data sheet ( Hoja de datos )
| Número de pieza | LM2403T | |
| Descripción | Monolithic Triple 4.5 nS CRT Driver | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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August 1999
LM2403
Monolithic Triple 4.5 nS CRT Driver
General Description
The LM2403 is an integrated high voltage CRT driver circuit
designed for use in high resolution color monitor applica-
tions. The IC contains three high input impedance, wide
band amplifiers which directly drive the RGB cathodes of a
CRT. Each channel has its gain internally set to −14 and can
drive CRT capacitive loads as well as resistive loads pre-
sented by other applications, limited only by the package’s
power dissipation.
The IC is packaged in an industry standard 11 lead TO-220
molded plastic power package. See thermal considerations
on page 5.
Features
n Rise/fall times typically 4.5 nS with 8 pF load at 40 Vpp
n Well matched with LM1283 video preamp
n Output swing capability: 60 Vpp for VCC = 80V
n 1V to 5V input range
n Stable with 0 pF–20 pF capacitive loads and inductive
peaking networks
n Convenient TO-220 staggered lead package style
n Standard LM240X Family Pinout which is designed for
easy PCB layout
Applications
n CRT driver for color monitors with display resolutions up
to 1600 x 1200
n Pixel clock frequency up to 160 MHz
Schematic and Connection Diagrams
DS100082-1
DS100082-2
Top View
Order Number LM2403T
FIGURE 1. Simplified Schematic Diagram (One Channel)
© 1999 National Semiconductor Corporation DS100082
www.national.com
1 page  
Application Hints (Continued)
will also help optimize rise and fall times as well as minimize
EMI. For proper arc protection, it is important to not omit any
of the arc protection components shown in Figure 10.
DS100082-10
FIGURE 10. One Channel of the LM2403 with the Recommended Arc Protection Circuit
OPTIMIZING TRANSIENT RESPONSE
Referring to Figure 10, there are three components (R1, R2
and L1) that can be adjusted to optimize the transient re-
sponse of the application circuit. Increasing the values of R1
and R2 will slow the circuit down while decreasing over-
shoot. Increasing the value of L1 will speed up the circuit as
well as increase overshoot. It is very important to use induc-
tors with very high self-resonant frequencies, preferably
above 300 MHz. Ferrite core inductors from J.W. Miller Mag-
netics (part # 78FR12M) were used for optimizing the perfor-
mance of the device in the NSC application board. The val-
ues shown in Figure 10 can be used as a good starting point
for the evaluation of the LM2403. The NSC demo board also
has a position open to add a resistor in parallel with L1. This
resistor can be used to help control overshoot. Using vari-
able resistors for R1 and the parallel resistor is a great way
to help dial in the values needed for optimum performance in
a given application.
Pull-up Resistors
Optimizing the performance of the LM2403 does require the
use of pull-up resistors at the outputs of the CRT driver.
These resistors are shown as R100, R101, and R102 in the
schematic. If you have a demo board form National please
note that these resistors have been added on the back of the
board since there is no PCB location for the pull-up resistors.
Because of the improved performance with these resistors,
all demo boards have been shipped with the added pull-up
resistors. The LM2403 does have some crossover distortion,
normal for any AB amplifier such as the LM2403. Adding the
pull-up resistors does add more bias to Q3 (Figure 1) thus
minimizing the crossover distortion. The LM2403 is normally
used in high end monitors, so it is highly recommended that
the 12k pull-up resistors be used in any design using the
LM2403. Selecting a 12k resistor provides the needed
pull-up current and limits the worst case power dissipation to
1/4W (white level at 25V).
In some applications pull-down resistors may be preferred.
Using 12k resistors gives acceptable performance, but this
will require the use of 1/2W resistors. Normally the power
save mode establishes whether pull-up or pull-down resis-
tors are preferred. If the setup of the power save mode in the
monitor gives a low output at the LM2403, then the pull-down
resistors would be preferred, if the 80V supply is still turned
on.
Effect of Load Capacitance
The output rise and fall times as well as overshoot will vary
as the load capacitance varies. The values of the output cir-
cuit (R1, R2 and L1 in Figure 10) should be chosen based on
the nominal load capacitance. Once this is done the perfor-
mance of the design can be checked by varying the load
based on what the expected variation will be.
For example, suppose you needed to drive a 10 pF (±20%)
load with a 40Vp-p waveform. First, you would pick the values
of R1, R2 and L1 that give the desired response with a 10 pF
load. Then you would test the design when driving an 8 pF
load and a 12 pF load. The table below summarizes the re-
sults from doing this exercise in a test board in the NSC lab.
The output signal swing was 40Vp-p from 65V to 25V.
Parameter
8 pF
10 pF
12 pF
Rise Time
4.1
4.2
4.3
Overshoot
1%
5% 10%
Fall Time
4.4
4.6
4.7
Overshoot
1%
2%
5%
The example above clearly demonstrates the importance of
having a good estimate of the range of the load capacitance.
Effect of Offset
Figure 7 shows the variation in rise and fall times when the
output offset of the device is varied from 30 VDC to 50 VDC.
The rise time shows about twice as much variation as the fall
time, however the maximum variation relative to the center
data point (40 VDC) is less than 10%.
Operation with VCC = 70V
The closed loop topography of the LM2403 allows operation
down to 10V above ground. If the user can limit the white
level between 10V and 20V, then operation with VCC = 70V
is possible. Operating the LM2403 with VCC = 70V will re-
quire the same current even though the supply voltage has
dropped by 12.5%. This results in a power savings of 12.5%
(as high a 1.5W), allowing a reduction in the size of the heat-
sink. Figure 8 shows the output waveform of the LM2403 op-
erating at a white level of 15V, and a peak-to-peak output
swing of 40V. Below is a summary of the LM2403 rise and
fall times with various output offset levels with VCC = 70V.
5 www.national.com
5 Page 
Physical Dimensions inches (millimeters) unless otherwise noted
NS Package Number TA11B
Order Number LM2403T
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: [email protected]
www.national.com
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Europe
Fax: +49 (0) 1 80-530 85 86
Email: [email protected]
Deutsch Tel: +49 (0) 1 80-530 85 85
English Tel: +49 (0) 1 80-532 78 32
Français Tel: +49 (0) 1 80-532 93 58
Italiano Tel: +49 (0) 1 80-534 16 80
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Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: [email protected]
National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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