LM1207AN National Semiconductor, LM1207AN Datasheet - Page 20

• Manufacturer Part Number: LM1207AN
• Manufacturer: National Semiconductor

Specifications of LM1207AN

• Power Supply Requirement: Single
• Dual Supply Voltage (typ): Not RequiredV
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Mounting: Through Hole
• Lead Free Status / RoHS Status: Not Compliant

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Circuit Description
Figure 14 also shows the power and ground pins to the
LM1205A/LM1207A. All the V
internally connected together. A 0.1 µF bypass capacitor
must be located close to each pin and connected to ground.
Further bypassing is done by a 100 µF capacitor. This ca-
pacitor needs to be located on the board close to the
LM1205A/LM1207A. Pins 22 and 23 are the V
10 µF and a 0.1 µF bypass capacitors must be located close
to pins 22 and 23. Correct bypassing of pins 22 and 23 is
very important . If the bypassing is not adequate then the
outputs of the LM1205A/LM1207A will have ringing, or even
worse they may oscillate. The ground side of the bypass ca-
pacitors at pins 22 and 23 must be returned to a ground
plane with no interruptions from other traces between these
capacitors and the ground pins 21 and 24 of the LM1205A/
LM1207A.
Applications of the
LM1205A/LM1207A
Figure 15 is the schematic of the demonstration board de-
signed at National. Figure 16 is the actual layout of the dem-
A 30
voltage surge may occur at these inputs when either the in-
puts are first connected to another system, or when the sys-
tem is powered up before the monitor is turned on. If this
voltage surge exceeds the supply voltage (at ground poten-
tial if the monitor is not powered up) of the LM1205A/
LM1207A, or goes below ground, current will flow through
the parasitic devices of the LM1205A/LM1207A. This current
resistor is in series with each of the video inputs. A
FIGURE 14. Simplified Schematic of LM1205A/LM1207A Video Amplifier Output Stage with Blank Circuit
CC1
(Continued)
pins (pins 3, 11, 25) are all
CC2
pins. A
20
onstration board. Note that the schematic shown in Figure
15 is almost identical to the schematic shown in Figure 4 .
The only difference between the two schematics is that in
Figure 15 each channel has individual adjustments for both
drive and cutoff, making this circuit a good design for monitor
applications. Each CRT will have a slightly different cutoff
voltage for each color, making it necessary to provide sepa-
rate adjustments in order to accurately set the cutoff for each
color. The gain of each color of the CRT is also slightly differ-
ent; if the color temperature of the display is to be accurately
set then each channel of the LM1205A/LM1207A must have
individual gain adjustments. Thus each channel has its own
drive control. Once the drive control is set, the gain between
the three color channels will closely track as the contrast is
adjusted. All the jumpers needed to design a single sided PC
board are shown in the schematic. The resistors and jump-
ers with no reference designation are the connections be-
tween the PC board and the connectors mounted on the PC
board. CN1 thru CN8 are BNC connectors.
is limited by the 30
strophic failure. A 100
and Clamp Gate inputs. These two resistors also limit the
current during a voltage surge. A larger resistor is required
because these inputs are DC coupled, allowing the current
to continuously flow into these inputs before the monitor is
resistors, preventing a potential cata-
resistor is added to the Blank Gate
DS012866-22