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參數(shù)資料
| 型號(hào)： | LM2476TB |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類(lèi)： | 音頻／視頻放大 |
| 英文描述： | 1 CHANNEL, VIDEO AMPLIFIER, PZFM19 |
| 封裝： | PLASTIC, TO-247, 19 PIN |
| 文件頁(yè)數(shù)： | 9/12頁(yè) |
| 文件大?。?/td> | 1235K |
| 代理商： | LM2476TB |
Typical Performance
Characteristics (V
CC = 85V, VBB = 8V, CL =8
pF, V
OUTD = 40VP-P (35V 75V), VINC = 2.35V, Test
Circuit - Figure 4 unless otherwise specified) (Continued)
Theory of Operation
The LM2476 is a high voltage monolithic three channel CRT
driver and triple bias clamp suitable for low-cost color moni-
tor applications. The LM2476 operates with 85V and 8V
power supplies. The part is housed in the 19-lead TO-247
molded plastic power package. The pinout and internal con-
nection diagram is shown in Figure 1.
The CRT Driver circuit diagram is shown in Figure 1. 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 27. 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 emitter follower stage to reduce cross-
over distortion at low signal levels. The typical driver DC
transfer function is shown in Figure 5.
The Bias Clamp circuit diagram is shown in Figure 3. The
clamp circuit amplifies the DC inputs, V
INC, by the internally
fixed gain of –16.5. Each clamp output, V
OUTC, will require a
pull-up resistor to V
CC. The typical clamp DC transfer func-
tion is shown in Figure 6.
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 LM2476 performance is targeted for the VGA (640 x
480) to XGA (1024 x 768, 85Hz) resolution market. The
application circuits shown in this document to optimize per-
formance and to protect against damage from CRT arcover
are designed specifically for the LM2476. If another member
of the NSC CRT Driver or Bias Clamp family is used, please
refer to its data sheet.
POWER SUPPLY BYPASS
Since the LM2476 contains wide bandwidth video amplifiers,
proper power supply bypassing is critical for optimum per-
formance. Improper power supply bypassing can result in
large overshoot, ringing or oscillation. 0.1 F capacitors
should be connected from the supply pins, V
CC and VBB,to
ground, as close to the LM2476 as is practical. Additionally,
a 47 F or larger electrolytic capacitor should be connected
from both supply pins to ground reasonably close to the
LM2476. For optimal supply bypassing, the bypass capaci-
tors should have the shortest connections between the sup-
ply and ground pins of the LM2476.
ARC PROTECTION
During normal CRT operation, internal arcing may occasion-
ally occur. A spark gap SG1 – in the range of 200V –
connected from each of the CRT cathodes to CRT ground
will limit the maximum voltage, but to a value that is much
higher than allowable on the LM2476. This fast, high voltage,
high energy pulse can damage the LM2476 driver and/or
clamp output stages. The application circuit shown in Figure
12 is designed to help clamp the voltage at the outputs of the
LM2476 to a safe level. The arc protection clamp diodes, D1
and D2, should have a fast transient response, high peak
current rating, low series impedance and low shunt capaci-
tance. FDH400 or equivalent diodes are recommended. Do
not use 1N4148 diodes for the clamp diodes. D1 and D2
should have short, low impedance connections to V
CC and
ground respectively. The cathode of D1 should be located
very close to a separately decoupled bypass capacitor (C1 in
Figure 12). The ground connection of D2 and the decoupling
capacitor should be closest to the CRT ground. This will
significantly reduce the high frequency voltage transients
that the LM2476 would be subjected to during an arcover
condition. Resistor R2 limits the arcover current that is seen
by the diodes while R1 limits the current into the LM2476 as
well as the voltage stress at the outputs of the device. R2
should be a 12W solid carbon type resistor. R1 can be a 14W
metal or carbon film type resistor. Having large value resis-
tors 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
LM2476 would be subjected to. The inductor will not only
help protect the device but it will also help minimize rise and
fall times as well as minimize EMI. Current-limiting resistor
R3 and bypass capacitor C2 should be placed very close to
the clamp output pins to protect the LM2476 against damage
during an arcover condition. The ground connection of C2
should have a short return path to CRT ground to shunt
arcover currents away from the LM2476. For proper arc
protection, it is important to not omit any of the arc protection
components shown in Figure 12.
20121907
FIGURE 11. Power Dissipation vs Frequency
LM2476
www.national.com
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2476TB/NOPB | 功能描述:顯示驅(qū)動(dòng)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(fēng)格:SMD/SMT 封裝 / 箱體:QFN-44 封裝:Reel |
| LM2479 | 制造商:NSC 制造商全稱(chēng):National Semiconductor 功能描述:120V Triple Bias Clamp |
| LM2479BN WAF | 制造商:Texas Instruments 功能描述: |
| LM2479NA | 制造商:NSC 制造商全稱(chēng):National Semiconductor 功能描述:120V Triple Bias Clamp |
| LM248 | 制造商:STMICROELECTRONICS 制造商全稱(chēng):STMicroelectronics 功能描述:QUAD BIPOLAR OPERATIONAL AMPLIFIERS |
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