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參數(shù)資料
| 型號： | LM2426 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Monolithic Triple Channel 30 MHz DTV Driver |
| 中文描述： | 單片三通道30兆赫數(shù)字電視驅(qū)動 |
| 文件頁數(shù)： | 7/12頁 |
| 文件大?。?/td> | 808K |
| 代理商： | LM2426 |
Application Hints
(Continued)
POWER SUPPLY BYPASS
Since the LM2426TE 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. 0.1μF capacitors should be con-
nected from the supply pins, V
and V
, to ground, as
close to the LM2426TE as is practical.Additionally, a 22μF or
larger electrolytic capacitor should be connected from both
supply pins to ground reasonably close to the LM2426TE.
ARC PROTECTION
During normal CRT operation, internal arcing may occasion-
ally occur. Spark gaps, in the range of 300V, connected from
the CRT cathodes to CRT ground will limit the maximum
voltage, but to a value that is much higher than allowable on
the LM2426TE. This fast, high voltage, high energy pulse
can damage the LM2426TE output stage. The application
circuit shown in
Figure 13
is designed to help clamp the
voltage at the output of the LM2426TE 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 capacitance. 1SS83 or equivalent diodes are
recommended. D1 and D2 should have short, low imped-
ance connections to V
CC
and ground respectively. The cath-
ode of D1 should be located very close to a separately
decoupled bypass capacitor (C3 in
Figure 13
). The ground
connection of D2 and the decoupling capacitor should be
very close to the LM2426TE ground. This will significantly
reduce the high frequency voltage transients that the
LM2426TE would be subjected to during an arcover condi-
tion. Resistor R2 limits the arcover current that is seen by the
diodes while R1 limits the current into the LM2426TE 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 LM2426TE
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. For proper arc protection, it is impor-
tant to not omit any of the arc protection components shown
in
Figure 13
.
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.
EFFECT OF OFFSET
Figure 8
shows the variation in rise and fall times when the
output offset of the device is varied from 105 to 115V
. The
rise time shows a variation of less than 7% relative to the
center data point (110V
). The fall time shows a variation of
less than 2% relative to the center data point.
THERMAL CONSIDERATIONS
Figure 9
shows the performance of the LM2426TE in the test
circuit shown in
Figure 3
as a function of case temperature.
The figure shows that the rise and fall times of the
LM2426TE increase by approximately 10% and 4%, respec-
tively, as the case temperature increases from 50C to 90C.
This corresponds to a speed degradation of 2.5% and 1% for
every 10C rise in case temperature.
Figure 10
shows the power dissipation of the LM2426TE vs.
Frequency when all three channels of the device are driving
an 8pF load with a 110V
alternating one pixel on, one pixel
off signal. The graph assumes a 72% active time (device
operating at the specified frequency) which is typical in a TV
application. The other 28% of the time the device is assumed
to be sitting at the black level (165V in this case).
Table 1
also shows the typical power dissipation of the LM2426TE
for various video patterns in the 480i, 480p, 720p, and 1080i
video formats.
Figure 10
,
Figure 11
, and
Table 1
give the designer the
information needed to determine the heatsink requirement
for the LM2426TE. For example, if an HDTV application
uses the 720p format and "Vertical Lines 2 On 2 Off" is
assumed to be the worst-case pattern to be displayed, then
the power dissipated will be 14.4W (from
Table 1
).
Figure 11
shows that the maximum allowed case temperature is 108C
when 14.4W is dissipated. If the maximum expected ambient
temperature is 70C, then a maximum heatsink thermal re-
sistance can be calculated:
This example assumes a capacitive load of 8pF and no
resistive load. The designer should note that if the load
capacitance is increased the AC component of the total
power dissipation will also increase.
Note: An LM126X preamplifier, with rise and fall times of
about 2 ns, was used to drive the LM2426TE for these power
measurements. Using a preamplifier with rise and fall times
slower than the LM126X will cause the LM2426TE to dissi-
pate less power than shown in
Table 1
.
OPTIMIZING TRANSIENT RESPONSE
In
Figure 13
, there are three components (R1, R2 and L1)
that can be adjusted to optimize the transient response of
the application circuit. Increasing the values of R1 and R2
will slow the circuit down while decreasing overshoot. In-
creasing the value of L1 will speed up the circuit as well as
increase overshoot. It is very important to use inductors with
very high self-resonant frequencies, preferably above 300
MHz. Ferrite core inductors from J.W. Miller Magnetics (part
#
78FR_ _k) were used for optimizing the performance of the
device in the NSC application board. The values shown in
Figure 14
and
Figure 15
can be used as a good starting point
for the evaluation of the LM2426TE. Using a variable resistor
for R1 will simplify finding the value needed for optimum
performance in a given application. Once the optimum value
is determined, the variable resistor can be replaced with a
fixed value.
20066410
FIGURE 13. One Channel of the LM2426TE with the
Recommended Application Circuit
L
www.national.com
7
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PDF描述 |
|---|---|
| LM2426TE | Monolithic Triple Channel 30 MHz DTV Driver |
| LM2429 | Monolithic Triple Channel 15 MHz DTV Driver |
| LM2432 | 220V Monolithic Single Channel 37 MHz HDTV CRT Driver |
| LM2432TE | 220V Monolithic Single Channel 37 MHz HDTV CRT Driver |
| LM2436 | Monolithic Triple 7.5 ns CRT Driver |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2426CT WAF | 制造商:Texas Instruments 功能描述: |
| LM2426TA | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| LM2426TE | 制造商:Rochester Electronics LLC 功能描述:DTV TRIPLE DRIVER, 30 MHZ, 180 - Bulk |
| LM2426TE/NOPB | 功能描述:IC DRIVER DTV 3CH 30MHZ 11-TO220 RoHS:是 類別:集成電路 (IC) >> PMIC - 顯示器驅(qū)動器 系列:- 產(chǎn)品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,500 系列:- 顯示器類型:真空熒光 (VF) 配置:5 x 7（矩陣） 接口:串行 數(shù)字或字符:- 電流 - 電源:3.5mA 電源電壓:2.7 V ~ 3.6 V 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:16-SSOP（0.154"，3.90mm 寬） 供應(yīng)商設(shè)備封裝:16-QSOP 包裝:帶卷 (TR) |
| LM2427 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Triple 80 MHz CRT Driver |
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