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LM2423 데이터시트 PDF




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부품번호 LM2423 기능
기능 220V Monolithic Triple Channel 15 MHz CRT DTV Driver
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LM2423 데이터시트, 핀배열, 회로
July 2004
LM2423
220V Monolithic Triple Channel 15 MHz CRT DTV Driver
General Description
The LM2423 is a triple channel high voltage CRT driver
circuit designed for use in DTV applications. 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 −54 and can drive CRT capacitive
loads as well as resistive loads present in 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 designed specifically to meet
high voltage spacing requirements. See Thermal Consider-
ations section.
n Up to 170VPP output swing with AC coupling to
cathodes
n 0V to 5V input voltage range
n Stable with 0 pF–20 pF capacitive loads and inductive
peaking networks
n Convenient TO-220 staggered thin lead package style
Applications
n AC coupled DTV applications using the 480p format as
well as standard NTSC and PAL formats.
Features
n 15 MHz bandwidth at 130VPP output swing
Connection Diagram
Schematic Diagram
20114801
FIGURE 1. Top View
Order Number LM2423TE
See NS Package Number TE11B NOPB
Available only with lead free plating
20114802
FIGURE 2. Simplified Schematic Diagram
(One Channel)
© 2004 National Semiconductor Corporation DS201148
www.national.com




LM2423 pdf, 반도체, 판매, 대치품
Typical Performance Characteristics (VCC = +220VDC, VBB = +12VDC, CL = 10 pF, VOUT = 130VPP
(60V – 190V), TC = 50˚C, Test Circuit — Figure 3 unless otherwise specified)
20114804
FIGURE 4. VOUT vs VIN
20114807
FIGURE 7. Speed vs Load Capacitance
20114805
FIGURE 5. LM2423 Pulse Response
20114808
FIGURE 8. Speed vs Offset
20114806
FIGURE 6. Bandwidth
20114809
FIGURE 9. Speed vs Case Temperature
www.national.com
4

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LM2423 전자부품, 판매, 대치품
Application Hints (Continued)
Figure 10 shows the maximum power dissipation of the
LM2423 vs. Frequency when all three channels of the device
are driving into a 10 pF load with a 130VP-P alternating one
pixel on, one pixel off. The graph assumes a 72% active time
(device operating at the specified frequency), which is typical
in a TV application. The other 28% of the time the device is
assumed to be sitting at the black level (190V in this case).
This graph gives the designer the information needed to
determine the heat sink requirement for his application. The
designer should note that if the load capacitance is in-
creased the AC component of the total power dissipation
would also increase.
The LM2423 case temperature must be maintained below
110˚C. If the maximum expected ambient temperature is
60˚C and the maximum power dissipation is 17W (from
Figure 10, 15 MHz) then a maximum heat sink thermal
resistance can be calculated:
This example assumes a capacitive load of 10 pF and no
resistive load. The designer should note that if the load
capacitance is increased the AC component of the total
power dissipation will also increase.
OPTIMIZING TRANSIENT RESPONSE
Referring to Figure 13, 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
Magnetics (part # 78FR--K) were used for optimizing the
performance of the device in the NSC application board. The
values shown in Figure 13 can be used as a good starting
point for the evaluation of the LM2423. Using a variable
resistor for R1 will simplify finding the value needed for
optimum performance in a given application. Once the opti-
mum value is determined the variable resistor can be re-
placed with a fixed value. Due to arc over considerations it is
recommended that the values shown in Figure 13 not be
changed by a large amount.
Figure 12 shows the typical cathode pulse response with an
output swing of 130VPP inside a modified Sony TV using a
Sony pre-amp.
PC BOARD LAYOUT CONSIDERATIONS
For optimum performance, an adequate ground plane, iso-
lation between channels, good supply bypassing and mini-
mizing unwanted feedback are necessary. Also, the length of
the signal traces from the signal inputs to the LM2423 and
from the LM2423 to the CRT cathode should be as short as
possible. The following references are recommended:
Ott, Henry W., “Noise Reduction Techniques in Electronic
Systems”, John Wiley & Sons, New York, 1976.
“Video Amplifier Design for Computer Monitors”, National
Semiconductor Application Note 1013.
Pease, Robert A., “Troubleshooting Analog Circuits”,
Butterworth-Heinemann, 1991.
Because of its high small signal bandwidth, the part may
oscillate in a TV if feedback occurs around the video channel
through the chassis wiring. To prevent this, leads to the video
amplifier input circuit should be shielded, and input circuit
wiring should be spaced as far as possible from output circuit
wiring.
TYPICAL APPLICATION
A typical application of the LM2423 is shown in the sche-
matic for the NSC demonstration board in Figure 14. Used in
conjunction with an LM1246 preamplifier, a complete video
channel from input to CRT cathode can be achieved. Perfor-
mance is ideal for DTV applications. The NSC demonstration
board can be used to evaluate the LM2423 combination with
the LM2485 and the LM1246 in a TV.
It is important that the TV designer use component values for
the driver output stage close to the values shown in Figure
14. These values have been selected to protect the LM2423
from arc over. Diodes D1, D2, D4, and D7–D9 must also be
used for proper arc over protection. The NSC demonstration
board can be used to evaluate the LM2423 in a TV. If the
NSC demonstration board is used for evaluating the
LM2423, then U3, the +5V voltage regulator may be used,
eliminating the need to route +5V to the neck board for the
LM1246.
NSC DEMONSTRATION BOARD
Figure 15 shows the routing and component placement on
the NSC LM2423/LM1246/LM2486 demonstration board.
This board provides a good example of a layout that can be
used as a guide for future layouts. Note the location of the
following components:
C19 — VCC bypass capacitor, located very close to pin 2
and ground pins
C20 — VBB bypass capacitor, located close to pin 11 and
ground
C46, C48 — VCC bypass capacitors, near LM2423 and
VCC clamp diodes. Very important for arc protection.
The routing of the LM2423 outputs to the CRT is very critical
to achieving optimum performance. Figure 16 shows the
routing and component placement from pin 10 (VOUT1) of the
LM2423 to the blue cathode. Note that the components are
placed so that they almost line up from the output pin of the
LM2423 to the blue cathode pin of the CRT connector. This
is done to minimize the length of the video path between
these two components. Note also that D8, D9, R24, and D6
are placed to minimize the size of the video nodes that they
are attached to. This minimizes parasitic capacitance in the
video path and also enhances the effectiveness of the pro-
tection diodes. The anode of protection diode D8 is con-
nected directly to a section of the ground plane that has a
short and direct path to the LM2423 ground pins. The cath-
ode of D9 is connected to VCC very close to decoupling
capacitor C7 which is connected to the same area of the
ground trace as D8. The diode placement and routing is very
important for minimizing the voltage stress on the LM2423
during an arc over event.
This demonstration board uses large PCB holes to accom-
modate socket pins, which function to allow for multiple
insertions of the LM2423 in a convenient manner. To benefit
from the enhanced LM2423 package with thin leads, the
device should be secured in small PCB holes to optimize the
metal-to-metal spacing between the leads.
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