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參數(shù)資料
| 型號： | LM2451TB |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 220V Monolithic Triple Channel 12 MHz DC Coupled CRT DTV Driver |
| 中文描述： | 3 CHANNEL, VIDEO AMPLIFIER, PSFM15 |
| 封裝： | LEAD FREE, PLASTIC, TO-247, 15 PIN |
| 文件頁數(shù)： | 6/12頁 |
| 文件大?。?/td> | 1101K |
| 代理商： | LM2451TB |
Theory of Operation
The LM2451 is a high voltage monolithic three channel CRT
driver suitable for DTV applications. The LM2451 operates
with 220V and 12V power supplies. The part is housed in a
15-lead TO-247 molded plastic power package with thin
leads for improved metal-to-metal spacing.
The circuit diagram of the LM2451 is shown in
Figure 2
. The
PNP emitter follower, Q5, provides input buffering. Q1 and
Q2 form a fixed gain cascode amplifier with resistors R1 and
R2 setting the gain at 54. An additional cascode amplifier is
formed by Q7 and Q2. Gain of this stage is set to —25 by
resistors R1 and R10. Q8 provides the input buffering for this
input. Q2 now becomes the summing point for both V
and
V
. Emitter followers Q3 and Q4 isolate the high output
impedance of the cascode stage from the capacitance of the
CRT cathode, which decreases the sensitivity of the device
to load capacitance. Q6 provides biasing to the output emit-
ter follower stage to reduce crossover distortion at low signal
levels.
Figure 3
shows a typical test circuit for evaluation of the
LM2451. This circuit is designed to allow testing of the
LM2451 in a 50
environment without the use of an expen-
sive FET probe. In this test circuit, the two 4.99 k
resistors
form a 400:1 wideband, low capacitance probe when con-
nected to a 50
coaxial cable and a 50
load (such as a
50
oscilloscope input). The input signal from the generator
is AC coupled to the video inputs of the LM2451.
Application Hints
INTRODUCTION
National Semiconductor (NSC) is committed to provide ap-
plication information that assists our customers in obtaining
the best performance possible from our products. The fol-
lowing information is provided in order to support this com-
mitment. The reader should be aware that the optimization of
performance was done using a specific printed circuit board
designed at NSC. Variations in performance can be realized
due to physical changes in the printed circuit board and the
application. Therefore, the designer should know that com-
ponent value changes may be required in order to optimize
performance in a given application. The values shown in this
document can be used as a starting point for evaluation
purposes. When working with high bandwidth circuits, good
layout practices are also critical to achieving maximum per-
formance.
IMPORTANT INFORMATION
The LM2451 performance is targeted for the HDTV market.
The application circuits shown in this document to optimize
performance and to protect against damage from CRT arc
over are designed specifically for the LM2451. If another
member of the LM245X family is used, please refer to its
datasheet.
POWER SUPPLY BYPASS
Since the LM2451 is a wide bandwidth amplifier, proper
power supply bypassing is critical for optimum performance.
Improper power supply bypassing can result in large over-
shoot, ringing or oscillation. 0.1 μF capacitors should be
connected from the supply pins, V
and V
, to ground, as
close to the LM2451 as is practical. Additionally, a 22 μF or
larger electrolytic capacitor should be connected from both
supply pins to ground reasonably close to the LM2451.
ARC PROTECTION
During normal CRT operation, internal arcing may occasion-
ally occur. This fast, high voltage, high-energy pulse can
damage the LM2451 output stage. The application circuit
shown in
Figure 13
is designed to help clamp the voltage at
the output of the LM2451 to a safe level. The clamp diodes,
D1 and D2, should have a fast transient response, high peak
current rating, low series impedance and low shunt capaci-
tance. 1SS83 or equivalent diodes are recommended. D1
and D2 should have short, low impedance connections to
V
and ground respectively. The cathode of D1 should be
located very close to a separately decoupled bypass capaci-
tor (C3 in
Figure 13
). The ground connection of D2 and the
decoupling capacitor should be very close to the LM2451
ground. This will significantly reduce the high frequency
voltage transients that the LM2451 would be subjected to
during an arc over condition. Resistor R2 limits the arc over
current that is seen by the diodes while R1 limits the current
into the LM2451 as well as the voltage stress at the outputs
of the device. R2 should be a
1
2
W solid carbon type resistor.
R1 can be a
1
4
W metal or carbon film type resistor. Having
large value resistors for R1 and R2 would be desirable, but
this has the effect of increasing rise and fall times. Inductor
L1 is critical to reduce the initial high frequency voltage
levels that the LM2451 would be subjected to before the
clamp diodes have a chance to became activated. The
inductor will not only help protect the device but it will also
help minimize rise and fall times as well as minimize EMI.
For proper arc protection, it is important to not omit any of the
arc protection components shown in
Figure 13
.
NOTE:
Do
not use spark gaps with the LM2451 when designing DC
coupled system. If a spark gap is triggered it shorts out the
output of the LM2451 and will destroy the part.
EFFECT OF LOAD CAPACITANCE
Figure 7
shows the effect of increased load capacitance on
the speed of the device. This demonstrates the importance
of knowing the load capacitance in the application. Increas-
ing the load capacitance from 10 pF to 20 pF adds about
14 ns to the rise time and about 18 ns to the fall time. It is
very important to keep the board capacitance as low as
possible to maximize the speed of the driver.
EFFECT OF OFFSET
Figure 8
shows the variation in rise and fall times when the
black level of the device is varied from 180V to 200V
. The
rise time increases only about 3 ns as the offset is increased
in voltage and the fall time decreases by about 7 ns with the
same offset adjustment.
20144413
FIGURE 13. One Channel of the LM2451 with the
Recommended Application Circuit
L
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2451TB/NOPB | 功能描述:顯示驅(qū)動器和控制器 RoHS:否 制造商:Panasonic Electronic Components 工作電源電壓:2.7 V to 5.5 V 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:QFN-44 封裝:Reel |
| LM2452 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:220V Monolithic Triple Channel 17 MHz DC Coupled CRT DTV Driver |
| LM2452TB | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:220V Monolithic Triple Channel 17 MHz DC Coupled CRT DTV Driver |
| LM2452TB/NOPB | 功能描述:顯示驅(qū)動器和控制器 RoHS:否 制造商:Panasonic Electronic Components 工作電源電壓:2.7 V to 5.5 V 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:QFN-44 封裝:Reel |
| LM2453 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Monolithic Triple 6 nS CRT Driver With Integrated Clamp and G1 Blanking |
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