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LM2452TB датащи(PDF) 8 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor.
номер детали LM2452TB
подробное описание детали  220V Monolithic Triple Channel 17 MHz DC Coupled CRT DTV Driver
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производитель  NSC [National Semiconductor (TI)]
домашняя страница  http://www.national.com
Logo NSC - National Semiconductor (TI)

LM2452TB датащи(HTML) 8 Page - National Semiconductor (TI)

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Application Hints (Continued)
NSC DEMONSTRATION BOARD
Figure 15 shows the routing and component placement on
the NSC LM2452 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 compo-
nents:
C26—V
CC bypass capacitor, located very close to pin 12
and ground pins
C27—V
BB bypass capacitor, located close to pin 7 and
ground
C28, C30, C33 — V
CC bypass capacitors, near LM2452
and V
CC clamp diodes. Very important for arc protection.
The routing of the LM2452 outputs to the CRT is very critical
to achieving optimum performance. Figure 16 shows the
routing and component placement from pin 13 (V
OUT3)ofthe
LM2452 to the blue cathode. Note that the components are
placed so that they almost line up from the output pin of the
LM2452 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 D1, D8 and R36 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 D1 is con-
nected directly to a section of the ground plane that has a
short and direct path to the heater ground and the LM2452
ground pins. The cathode of D8 is connected to V
CC very
close to decoupling capacitor C28 which is connected to the
same area of the ground trace as D1. The diode placement
and routing is very important for minimizing the voltage
stress on the LM2452 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 LM2452 in a convenient manner. To benefit
from the enhanced LM2452 package with thin leads, the
device should be secured in small PCB holes to optimize the
metal-to-metal spacing between the leads.
CURRENT OUTPUT FOR IK FEEDBACK SYSTEMS
The LM2452 can be used in DTV applications that use an IK
feedback system. Figure 14 shows an example of an inter-
face circuit used to feed back the IK output of LM2452 to a
preamplifier with an ac coupled IK input.
This feedback system consists of the preamp, LM2452, and
interface circuit, forming a closed loop to automatically ad-
just the black level of the drive signals to the cutoff point of
the RGB cathodes. Following is a description of the interface
circuit operation used for AVPs that have a voltage input for
their IK sense input.
The output at pin 8 of the LM2452 is filtered of high fre-
quency noise by C14. D7 is used to limit the peak voltage at
pin 8. Without this clamp diode the voltage would easily
exceed 12V during active video when the cathode currents
are much greater than the small currents being detected
during vertical blanking. Exceeding 12V could damage Q1
and result in improper operation of the driver.
R35 is essential to convert the IK current to voltage. Choos-
ing the value of R35 sets the gain of the feedback voltage,
and consequently, the operating point of the tube. Once a
stable operating point is established, this point can be fine-
tuned using the adjustment range of the feedback system or
standard preamp controls. Changing the value of R35 will
change the cutoff voltage at the cathode. A smaller value of
R35 requires more IK current to maintain the feedback loop.
The cutoff voltage set at the cathode will be lower to adjust to
the higher IK current. This additional current must come from
the cathode; therefore, the cathode voltage is set lower to
meet higher current requirement. A higher value of R35 will
do the opposite, raising the cathode voltage because less IK
current is needed to maintain the same voltage at R35.
The emitter follower, Q7, isolates R35 from the input imped-
ance of the preamp. R21 and R39 bias the emitter of Q7 to
limit the maximum voltage to the preamp. These resistor
values should be chosen to limit the maximum voltage at the
emitter and protect the preamp from any large voltages that
would otherwise occur during active video. C9 is used to AC
couple the IK signal to the preamp. The advantage of AC
coupling is that any DC component (leakage current from the
driver) of the IK signal is not detected by the IK sense input
of the preamp.
Some AVPs do have a direct current input for their IK sense
input. For interfacing to these AVPs the only components to
be used in the IK sense section are D7 and R41. To com-
plete the signal path a jumper must be used to replace R34,
C9 and the base-emitter junction of Q7. C14 can still be used
for high frequency filtering.
www.national.com
8


Аналогичный номер детали - LM2452TB

производительномер деталидатащиподробное описание детали
logo
National Semiconductor ...
LM2450 NSC-LM2450 Datasheet
1Mb / 12P
   220V Monolithic Triple Channel 7 MHz DC Coupled CRT DTV Driver
logo
Texas Instruments
LM2450 TI1-LM2450 Datasheet
3Mb / 14P
[Old version datasheet]   Monolithic Triple Channel 7 MHz DC Coupled CRT DTV Driver
logo
National Semiconductor ...
LM2451 NSC-LM2451 Datasheet
1Mb / 12P
   220V Monolithic Triple Channel 12 MHz DC Coupled CRT DTV Driver
logo
Texas Instruments
LM2451 TI1-LM2451 Datasheet
3Mb / 14P
[Old version datasheet]   Monolithic Triple Channel 12 MHz DC Coupled CRT DTV Driver
logo
National Semiconductor ...
LM2451TB NSC-LM2451TB Datasheet
1Mb / 12P
   220V Monolithic Triple Channel 12 MHz DC Coupled CRT DTV Driver
More results

Аналогичное описание - LM2452TB

производительномер деталидатащиподробное описание детали
logo
National Semiconductor ...
LM2450 NSC-LM2450 Datasheet
1Mb / 12P
   220V Monolithic Triple Channel 7 MHz DC Coupled CRT DTV Driver
LM2451 NSC-LM2451 Datasheet
1Mb / 12P
   220V Monolithic Triple Channel 12 MHz DC Coupled CRT DTV Driver
LM2425 NSC-LM2425 Datasheet
1Mb / 11P
   220V Monolithic Triple Channel 10 MHz CRT DTV Driver
LM2423 NSC-LM2423 Datasheet
733Kb / 11P
   220V Monolithic Triple Channel 15 MHz CRT DTV Driver
LM2422 NSC-LM2422 Datasheet
603Kb / 8P
   220V Monolithic Triple Channel 30 MHz CRT DTV Driver
LM2423 NSC-LM2423_06 Datasheet
1Mb / 11P
   220V Monolithic Triple Channel 15 MHz CRT DTV Driver
LM2422TE NSC-LM2422TE Datasheet
1Mb / 13P
   220V Monolithic Triple Channel 30 MHz CRT DTV Driver
LM2422_0505 NSC-LM2422_0505 Datasheet
602Kb / 8P
   220V Monolithic Triple Channel 30 MHz CRT DTV Driver
logo
Texas Instruments
LM2450 TI1-LM2450 Datasheet
3Mb / 14P
[Old version datasheet]   Monolithic Triple Channel 7 MHz DC Coupled CRT DTV Driver
LM2451 TI1-LM2451 Datasheet
3Mb / 14P
[Old version datasheet]   Monolithic Triple Channel 12 MHz DC Coupled CRT DTV Driver
More results


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