lm2412a National Semiconductor Corporation, lm2412a Datasheet - Page 6

• Manufacturer Part Number: lm2412a
• Description: Monolithic Triple 2.8 Ns Crt Driver
• Manufacturer: National Semiconductor Corporation

www.national.com
Application Hints
NSC Demonstration Board
Figures 11, 12 show routing and component placement on
the NSC LM2202/2412 demonstration board. The schematic
of the board is shown in Figure 10 . 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 compo-
nents:
The routing of the LM2412A outputs to the CRT is very
critical to achieving optimum performance. Figure 13 shows
the routing and component placement from pin 1 to the blue
• C47 - V
• C49 - V
• C46 and C77 - V
and ground pins. ( Figure 12 )
ground. ( Figure 12 )
and V
( Figure 11 )
CC
BB
CC
clamp diodes. Very important for arc protection.
bypass capacitor, located close to pin 10 and
bypass capacitor, located very close to pin 6
CC
bypass capacitors, near LM2412A
(Continued)
6
cathode. Note that the components are placed so that they
almost line up from the output pin of the LM2412A to the blue
cathode pin of the CRT connector. This is done to minimize
the length of the video path between these two components.
The direct video path is shown in by a dark gray line through
the components and the PCB traces. Note also that D24,
D25, R58 and D19 are placed to keep the size of the video
nodes to a minimum (R58 is located under D19). This mini-
mizes parasitic capacitance in the video path and also en-
hances the effectiveness of the protection diodes. The traces
in the video nodes to these components are shown by the
white line. The anode of protection diode D25 is connected
directly to the ground plane giving a short and direct path to
the LM2412A ground pins. The cathode of D24 is connected
to V
which is connected to the same section of the ground plane
as D25. The diode placement and routing is very important
for minimizing the voltage stress on the LM2412A during an
arc-over event. Lastly, notice that S3 is placed very close to
the blue cathode and is tied directly to CRT ground.
CC
very close to decoupling capacitor C78 ( Figure 13 )