LM2467TA [ROCHESTER]

3 CHANNEL, VIDEO AMPLIFIER, PZFM9, TO-220, 9 PIN;


型号：	LM2467TA
厂家：	Rochester Electronics
描述：	3 CHANNEL, VIDEO AMPLIFIER, PZFM9, TO-220, 9 PIN 局域网放大器商用集成电路
文件：	总13页 (文件大小：1132K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

October 2000

LM2467

Monolithic Triple 7.5 ns CRT Driver

General Description

Features

n Higher gain to match LM126X CMOS preamplifiers

n 0V to 3.75V input range

The LM2467 is an integrated high voltage CRT driver circuit

designed for use in color monitor applications. The IC con-

tains three high input impedance, wide band amplifiers

which directly drive the RGB cathodes of a CRT. Each

channel has its gain internally set to −20 and can drive CRT

capacitive loads as well as resistive loads present in other

applications, limited only by the package’s power dissipation.

n Stable with 0–20 pF capacitive loads and inductive

peaking networks

n Convenient TO-220 staggered lead package style

n Maintains standard LM243X Family pinout which is

designed for easy PCB layout

The IC is packaged in an industry standard 9-lead TO-220

molded plastic power package. See Thermal Considerations

section.

Applications

n 1024 x 768 displays up to 85 Hz refresh

n Pixel clock frequencies up to 95 MHz

n Monitors using video blanking

Schematic and Connection Diagrams

DS200078-2

Note: Tab is at GND

Top View

Order Number LM2467T

DS200078-1

FIGURE 1. Simplified Schematic Diagram

(One Channel)

DS200078

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Absolute Maximum Ratings (Notes 1, 3)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Lead Temperature

(Soldering, 10 sec.)

300˚C

2 kV

ESD Tolerance, Human Body Model

Machine Model

250V

Supply Voltage (V_CC

)

+90V

+16V

Operating Ranges (Note 2)

Bias Voltage (V_BB

)

Input Voltage (V_IN

0V to 4.5V

V_CC

+60V to +85V

+8V to +15V

Storage Temperature Range (T_STG

)

−65˚C to +150˚C

V_BB

V_IN

+0V to +3.75V

+15V to +75V

−20˚C to +100˚C

V_OUT

Case Temperature

Do not operate the part without a heat sink.

Electrical Characteristics

(See Figure 2 for Test Circuit)

Unless otherwise noted: V_CC= +80V, V_BB= +12V, C_L= 8 pF, T_C= 50˚C

DC Tests: V_IN= 2.25VDC

AC Tests: Output = 40V_PP(25V - 65V) at 1MHz

LM2467

Typical

Symbol

Parameter

Supply Current

Conditions

Units

Min

Max

I_CC

All Three Channels, No Input Signal,

No Output Load

I_BB

V_OUT

A_V

Bias Current

DC Output Voltage

DC Voltage Gain

Gain Matching

Linearity Error

Rise Time

All Three Channels

−20

1.0

No AC Input Signal, V_IN= 1.25V

No AC Input Signal

V_DC

−18

−22

∆A_V

(Note 4), No AC Input Signal

(Notes 4, 5), No AC Input Signal

(Note 6), 10% to 90%

(Note 6), 90% to 10%

(Note 6)

t_R

7.5

t_F

Fall Time

Overshoot

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur.

Note 2: Operating ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. For guaranteed specifications and

test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics may

change when the device is not operated under the listed test conditions.

Note 3: All voltages are measured with respect to GND, unless otherwise specified.

Note 4: Calculated value from Voltage Gain test on each channel.

Note 5: Linearity Error is the variation in dc gain from V = 1.0V to V = 3.5V.

Note 6: Input from signal generator: t , t

1 ns.

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AC Test Circuit

DS200078-3

Note: 8 pF load includes parasitic capacitance.

FIGURE 2. Test Circuit (One Channel)

Figure 2 shows a typical test circuit for evaluation of the LM2467. This circuit is designed to allow testing of the LM2467 in a 50Ω

environment without the use of an expensive FET probe. The two 2490Ω resistors form a 200:1 divider with the 50Ω resistor and

the oscilloscope. A test point is included for easy use of an oscilloscope probe.The compensation capacitor is used to

compensate the stray capacitance of the two 2490Ω resistors to achieve flat frequency response.

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Typical Performance Characteristics (V_CC= +80 V_DC, V_BB= +12 V_DC, C_L= 8 pF, V_OUT= 40 V_PP

(25V−65V), Test Circuit - Figure 2 unless otherwise specified)

DS200078-4

DS200078-7

FIGURE 3. V_OUTvs V_IN

FIGURE 6. Power Dissipation vs Frequency

DS200078-5

DS200078-8

FIGURE 4. Speed vs Temp.

FIGURE 7. Speed vs Offset

DS200078-6

FIGURE 5. LM2467 Pulse Response

DS200078-9

FIGURE 8. Speed vs Load Capacitance

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ARC PROTECTION

Theory of Operation

During normal CRT operation, internal arcing may occasion-

ally occur. Spark gaps, in the range of 200V, 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 LM2467. This fast, high voltage, high energy pulse can

damage the LM2467 output stage. The application circuit

shown in Figure 9 is designed to help clamp the voltage at

the output of the LM2467 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. 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_CCand

ground respectively. The cathode of D1 should be located

very close to a separately decoupled bypass capacitor (C3 in

Figure 9). The ground connection of D2 and the decoupling

capacitor should be very close to the LM2467 ground. This

will significantly reduce the high frequency voltage transients

that the LM2467 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 LM2467 as

well as the voltage stress at the outputs of the device. R2

The LM2467 is a high voltage monolithic three channel CRT

driver suitable for high resolution display applications. The

LM2467 operates with 80V and 12V power supplies. The

part is housed in the industry standard 9-lead TO-220

molded plastic power package.

The circuit diagram of the LM2467 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 −20. 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.

Figure 2 shows a typical test circuit for evaluation of the

LM2467. This circuit is designed to allow testing of the

LM2467 in a 50Ω environment without the use of an expen-

sive FET probe. In this test circuit, the two 4.95kΩ resistors

form a 200:1 wideband, low capacitance probe when con-

nected to a 50Ω coaxial cable and a 50Ω load (such as a

50Ω oscilloscope input). The input signal from the generator

is ac coupled to the base of Q5.

should be a ¹⁄

W solid carbon type resistor. R1 can be a ¹⁄

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

LM2467 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 important to not omit any of the arc protection compo-

nents shown in Figure 9.

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 LM2467 performance is targeted for the VGA (640 x

480) to XGA (1024 x 768, 85 Hz refresh) resolution market.

The application circuits shown in this document to optimize

performance and to protect against damage from CRT ar-

cover are designed specifically for the LM2467. If another

member of the LM246X family is used, please refer to its

datasheet.

POWER SUPPLY BYPASS

Since the LM2467 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_CCand V_BB, to ground, as

close to the LM2467 as is practical. Additionally, a 47 µF or

larger electrolytic capacitor should be connected from both

supply pins to ground reasonably close to the LM2467.

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Application Hints (Continued)

DS200078-10

FIGURE 9. One Channel of the LM2467 with the Recommended Arc Protection Circuit

OPTIMIZING TRANSIENT RESPONSE

cation. The designer should note that if the load capacitance

is increased the AC component of the total power dissipation

will also increase.

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

Magnetics (part # 78FR--k) were used for optimizing the

performance of the device in the NSC application board. The

values shown in Figure 10 and Figure 11 can be used as a

good starting point for the evaluation of the LM2467. Using

variable resistors for R1 and the parallel resistor will simplify

finding the values needed for optimum performance in a

given application. Once the optimum values are determined

the variable resistors can be replaced with fixed values.

The LM2467 case temperature must be maintained below

100˚C. If the maximum expected ambient temperature is

70˚C and the maximum power dissipation is 4.3W (from

Figure 6, 50 MHz bandwidth) then a maximum heat sink

thermal resistance can be calculated:

This example assumes a capacitive load of 8 pF and no

resistive load.

TYPICAL APPLICATION

A typical application of the LM2467 is shown in Figure 10

and Figure 11. Used in conjunction with an LM1267, a com-

plete video channel from monitor input to CRT cathode can

be achieved. Performance is ideal for 1024 x 768 resolution

displays with pixel clock frequencies up to 95 MHz. Figure 10

and Figure 11 are the schematic for the NSC demonstration

board that can be used to evaluate the LM1267/2467 com-

bination in a monitor.

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.

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_DC. The

rise time shows a maximum variation relative to the center

data point (45 V_DC) less than 5%. The fall time shows a

variation of less than 5% relative to the center data point.

PC BOARD LAYOUT CONSIDERATIONS

For optimum performance, an adequate ground plane, iso-

lation between channels, good supply bypassing and mini-

mizing unwanted feedback are necessary. Also, the length of

the signal traces from the preamplifier to the LM2467 and

from the LM2467 to the CRT cathode should be as short as

possible. The following references are recommended:

THERMAL CONSIDERATIONS

Figure 4 shows the performance of the LM2467 in the test

circuit shown in Figure 2 as a function of case temperature.

The figure shows that the rise time of the LM2467 increases

by approximately 10% as the case temperature increases

from 50˚C to 100˚C. This corresponds to a speed degrada-

tion of 2% for every 10˚C rise in case temperature.There is a

negligible change in fall time vs. temperature in the test

circuit.

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 Analog Circuits”,

Butterworth-Heinemann, 1991.

Because of its high small signal bandwidth, the part may

oscillate in a monitor if feedback occurs around the video

channel through the chassis wiring. To prevent this, leads to

the video amplifier input circuit should be shielded, and input

circuit wiring should be spaced as far as possible from output

circuit wiring.

Figure 6 shows the maximum power dissipation of the

LM2467 vs. Frequency when all three channels of the device

are driving an 8 pF load with a 40 V_p-palternating 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-

NSC DEMONSTRATION BOARD

Figure 12 shows the routing and component placement on

the NSC LM1267/2467 demonstration board. The schematic

of the board is shown in Figure 10 and Figure 11. This board

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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 D8, D9, R24 and D6 are placed

to minimize the size of the video nodes that they are at-

tached to. This minimizes parasitic capacitance in the video

path and also enhances the effectiveness of the protection

diodes. The anode of protection diode D8 is connected

directly to a section of the the ground plane that has a short

and direct path to the LM2467 ground pins. The cathode of

D9 is connected to V_CCvery close to decoupling capacitor

C19 (see Figure 13) which is connected to the same section

of the ground plane as D8. The diode placement and routing

is very important for minimizing the voltage stress on the

LM2467 during an arcover event. Lastly, notice that S3 is

placed very close to the blue cathode and is tied directly to

CRT ground.

Application Hints (Continued)

provides a good example of a layout that can be used as a

guide for future layouts. Note the location of the following

components:

•

C19—V_CCbypass capacitor, located very close to pin 4

and ground pins

C20—V_BBbypass capacitors, located close to pin 8 and

ground

C46, C47, C48—V_CCbypass capacitors, near LM2467

and V_CCclamp diodes. Very important for arc protection.

The routing of the LM2467 outputs to the CRT is very critical

to achieving optimum performance. Figure 13 shows the

routing and component placement from pin 1 of the LM2467

to the blue cathode. Note that the components are placed so

that they almost line up from the output pin of the LM2467 to

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Application Hints (Continued)

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Application Hints (Continued)

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Application Hints (Continued)

DS200078-13

FIGURE 12. LM126X/LM246X Demo Board Layout

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Application Hints (Continued)

DS200078-14

FIGURE 13. Trace Routing and Component Placement for Blue Channel Output

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Physical Dimensions inches (millimeters) unless otherwise noted

CONTROLLING DIMENSION IS INCH

VALUES IN [ ] ARE MILLIMETERS

NS Package Number TA09A

Order Number LM2467TA

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DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL

COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or

systems which, (a) are intended for surgical implant

into the body, or (b) support or sustain life, and

whose failure to perform when properly used in

accordance with instructions for use provided in the

labeling, can be reasonably expected to result in a

significant injury to the user.

2. A critical component is any component of a life

support device or system whose failure to perform

can be reasonably expected to cause the failure of

the life support device or system, or to affect its

safety or effectiveness.

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National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

LM2467TA [ROCHESTER]

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