LM1253AN National Semiconductor, LM1253AN Datasheet - Page 16

• Manufacturer Part Number: LM1253AN
• Description: Monolithic Triple 180 MHz I2C CRT Pre-amp With Integrated Analog On Screen Display (OSD) Generator
• Manufacturer: National Semiconductor

www.national.com
National VideoPlex Video System
ESD and Arc-Over Protection
The LM1253A incorporates full ESD protection with special
consideration given to maximizing arc-over robustness. The
monitor designer must still use good circuit design and PCB
layout techniques. The human body model ESD susceptibil-
ity of the LM1253A is 2 kV, however many monitor manufac-
turers are now testing their monitors to the level 4 of the IEC
801-2 specification which requires the monitor to survive an
8 kV discharge. External ESD protection is needed to sur-
vive this level of ESD. The LM1253A provides excellent pro-
tection against both ESD and arc-over, but this is not a sub-
stitute for good PCB layout.
Figure 26 show the recommended input protection for the
LM1253A. This provides the best protection against ESD.
When this protection is combined with good PCB layout the
LM1253A will easily survive the IEC 801-2 level 4 testing
(8 kV ESD). It is strongly recommended that the protection
diodes be added as shown in Figure 26 . The 1N4148 diode
has a maximum capacitance of 4 pF which will have little ef-
fect on the response of the video system due to the low im-
pedance of the input video.
The ESD cells of the LM1253A also provide good protection
against arc-over, however good PCB layout is necessary.
The LM1253A should not be exposed directly to the voltages
that may occur during arc-over. The main vulnerability of the
LM1253A to arc-over is though the ground traces on the
PCB. For proper protection all ground connections associ-
ated with the LM1253A, including the grounds to the bypass
FIGURE 24. DC I/O Transfer Characteristics for the LM2453 CRT Driver
(Test Conditions: V
FIGURE 25. LM2453 Input and Output Waveforms
REF
(Continued)
= 1.65V, V
16
capacitors, must have short returns to the ground pins. A sig-
nificant ground plane should be used to connect all the
LM1253A grounds. Figure 31 , which shows the demo board
layout, is an excellent example of an effective ground plane.
The list below should be followed to ensure a PCB with good
grounding:
• All grounds associated with the LM1253A should be con-
• CRT driver ground is connected to the video pre-amp
• CRT and arc protection grounds are connected directly to
• Input signal traces for SDA, SCL, H Flyback, V Flyback,
• Output signal traces of the LM1253A (video, V
If any one of the above suggestions is not followed the
LM1253A may become more vulnerable to arc-over. Im-
proper grounding is by far the most common cause of a
video pre-amp failure during arc-over.
CC1
nected together through a large ground plane.
ground at one point.
the chassis or main ground. There is no arc-over current
flow from these grounds through the LM1253A grounds.
Clamp should be kept away from the LM2453 and all
traces that an arc can travel on.
V
put signals of the LM2453.
REF
= 80V, V
) should be kept away from traces that carry the out-
DS101265-27
BB
= 8V)
DS101265-28
BLANK
,