lm2466 National Semiconductor Corporation, lm2466 Datasheet - Page 8

• Manufacturer Part Number: lm2466
• Description: Monolithic Triple 7.5 Ns Crt Driver
• Manufacturer: National Semiconductor Corporation

www.national.com
Application Hints
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 preamplifier to the LM2466 and
from the LM2466 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.
Channel
Red
Green
Blue
TABLE 1. LM2466 Cathode Response
FIGURE 10. Red Cathode Response
t
6.3ns / 7%
6.1ns / 6%
6.5ns / 3%
r
/OS
(Continued)
20043616
t
6.3ns / 3%
5.9ns / 4%
6.4ns / 2%
f
/OS
8
Because of its high small signal bandwidth, the part may
oscillate in a monitor 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.
NSC DEMONSTRATION BOARD
Figure 13 shows the routing and component placement on
the NSC LM1267/2466 demonstration board. The schematic
of the board is shown in Figure 11 and Figure 12. 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 — V
• C20 — V
• C46, C47, C48 — V
The routing of the LM2466 outputs to the CRT is very critical
to achieving optimum performance. Figure 14 shows the
routing and component placement from pin 1 of the LM2466
to the blue cathode. Note that the components are placed so
that they almost line up from the output pin of the LM2466 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 at-
tached to. This minimizes parasitic capacitance in the video
path and also enhances the effectiveness of the protection
diodes. The anode of protection diode D8 is connected
directly to a section of the the ground plane that has a short
and direct path to the LM2466 ground pins. The cathode of
D9 is connected to V
C19 (see Figure 14) which is connected to the same section
of the ground plane as D8. The diode placement and routing
is very important for minimizing the voltage stress on the
LM2466 during an arcover event. Lastly, notice that S3 is
placed very close to the blue cathode and is tied directly to
CRT ground.
and ground pins
ground
and V
CC
CC
BB
clamp diodes. Very important for arc protection.
bypass capacitors, located close to pin 8 and
bypass capacitor, located very close to pin 4
CC
CC
very close to decoupling capacitor
bypass capacitors, near LM2466