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參數(shù)資料
| 型號(hào)： | LM2438T |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | Monolithic Triple 13.5 ns CRT Driver |
| 中文描述： | 3 CHANNEL, VIDEO AMPLIFIER, PZFM9 |
| 封裝： | PLASTIC, TO-220, 9 PIN |
| 文件頁數(shù)： | 6/11頁 |
| 文件大?。?/td> | 613K |
| 代理商： | LM2438T |
Application Hints
(Continued)
OPTIMIZING TRANSIENT RESPONSE
Referring to Figure 9 there are three components (R1, R2
and L1) that can be adjusted to optimize the transient re-
sponse of the application circuit. Increasing the values of R1
and R2 will slow the circuit down while decreasing over-
shoot. Increasing the value of L1 will speed up the circuit as
well as increase overshoot. It is very important to use induc-
tors with very high self-resonant frequencies, preferably
above 300 MHz. Ferrite core inductors from J.W. Miller Mag-
netics (part
#
78F1R8K) were used for optimizing the perfor-
mance of the device in the NSC application board. The val-
ues shown in Figure 9 can be used as a good starting point
for the evaluation of the LM2438. Using a variable resistor
for R1 will simplify finding the value needed for optimum per-
formance in a given application. Once the optimum value is
determined the variable resistor can be replaced with a fixed
value.
EFFECT OF LOAD CAPACITANCE
Figure 8 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. Figure 8
also shows the effect inductance has on the rise and fall
times.
EFFECT OF OFFSET
Figure 7 shows the variation in rise and fall times when the
output offset of the device is varied from 40 to 50 V
. The
rise time shows a maximum variation relative to the center
data point (45 V
) of about 2%. The fall time shows a varia-
tion of about 2% relative to the center data point.
THERMAL CONSIDERATIONS
Figure 4 shows the performance of the LM2438 in the test
circuit shown in Figure 2 as a function of case temperature.
The figure shows that the rise time of the LM2438 increases
by approximately 5% as the case temperature increases
from 50C to 100C. This corresponds to a speed degrada-
tion of 1% for every 10C rise in case temperature. The fall
time increases by approximately 7.5% as the case tempera-
ture increases from 50C to 100C. This corresponds to a
speed degradation of 1.5% for every 10C rise in case tem-
perature.
Figure 6 shows the maximum power dissipation of the
LM2438 vs. Frequency when all three channels of the device
are driving an 8 pF load with a 40 V
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 monitor application. The other 28% of the time
the device is assumed to be sitting at the black level (65V in
this case). This graph gives the designer the information
needed to determine the heat sink requirement for his appli-
cation. The designer should note that if the load capacitance
is increased the AC component of the total power dissipation
will also increase.
The LM2438 case temperature must be maintained below
100C. If the maximum expected ambient temperature is
70C and the maximum power dissipation is 2.6W (from Fig-
ure 6 30 MHz bandwidth) then a maximum heat sink thermal
resistance can be calculated:
This example assumes a capacitive load of 8 pF and no re-
sistive load.
TYPICAL APPLICATION
A typical application of the LM2438 is shown in Figure 11
Used in conjunction with an LM1279, a complete video chan-
nel from monitor input to CRT cathode can be achieved. Per-
formance is ideal for 1024 x 768 resolution displays with
pixel clock frequencies up to 60 MHz. Figure 11 is the sche-
matic for the NSC demonstration board that can be used to
evaluate the LM1279/2438 combination in a monitor.
PC BOARD LAYOUT CONSIDERATIONS
For optimum performance, an adequate ground plane, isola-
tion between channels, good supply bypassing and minimiz-
ing unwanted feedback are necessary.Also, the length of the
signal traces from the preamplifier to the LM2438 and from
the LM2438 to the CRT cathode should be as short as pos-
sible. The following references are recommended:
Ott, Henry W., “Noise Reduction Techniques in Electronic
Systems”, John Wiley & Sons, New York, 1976.
“Video Amplifier Design for Computer Monitors”, National
Semiconductor Application Note 1013.
Pease,
Robert
A.,
“Troubleshooting
Butterworth-Heinemann, 1991.
Because of its high small signal bandwidth, the part may os-
cillate in a monitor if feedback occurs around the video chan-
nel through the chassis wiring. To prevent this, leads to the
video amplifier input circuit should be shielded, and input cir-
cuit wiring should be spaced as far as possible from output
circuit wiring.
Analog
Circuits”,
DS101043-10
FIGURE 9. One Channel of the LM2438 with the Recommended Application Circuit
www.national.com
6
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
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| LM2439T | 制造商:Rochester Electronics LLC 功能描述:MONOLITHIC TRP 9.5NS CRT DRVR - Bulk |
| LM2439T/NOPB | 功能描述:IC DRIVER MONOLITHIC TO-220-9 RoHS:是 類別:集成電路 (IC) >> PMIC - 顯示器驅(qū)動(dòng)器 系列:- 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)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) |
| LM2445 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Monolithic Triple 7.5 ns CRT Driver |
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