Datasheet LM2469TA Datasheet (NSC)

LM2469
Monolothic Triple 9nS High Gain CRT Driver

LM2469 Monolothic Triple 9nS High Gain CRT Driver

October 2000

General Description

The LM2469 is an integrated high voltage CRT driver circuit
designed for use in color monitor applications. The IC con­tains 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, limitedonly by the package’s power dissipation.

The IC is packaged in an industry standard 9 lead TO-220
molded plastic package.

n 0V to 3.75V input range
n Stable with 0-20pF capacitive loads and inductive

peaking networks

n Maintains standard LM243X Family Pinout which is

designed for easy PCB layout

n Convenient TO-220 staggered 9 lead package style

Applications

n Up to 1024 X 768 at 70Hz
n Pixel clock frequencies up to 75MHz
n Monitors using video blanking

Features

n Higher gain to match LM126X CMOS preamplifiers

Schematic Diagram Connection Diagram

DS200006-2

Note: Tab is at GND.

DS200006-1

FIGURE 1. Simplified Schematic Diagram (One

Channel)

© 2000 National Semiconductor Corporation DS200006 www.national.com

FIGURE 2. Top View

Order Number: LM2469TA

NS package Number: TA09A

Absolute Maximum Ratings (Notes 1, 3)

If Military/Aerospace specified devices are required,

LM2469

please contactthe National Semiconductor Sales Office/
Distributors for availability and specifications.

Supply Voltage, V
Bias Voltage, V
Input Voltage, V
Storage Temperature Range, T

CC

BB

IN

STG

-65˚C to +150˚C

+90V
+16V

0V to 4.5V

Limits of Operating Ranges (Note 2)

V

CC

V

BB

V

IN

V

OUT

Case Temperature -20˚C to +100˚C

Do not operate the part without a heat sink.

+60V to +85V

+8V to 15V

0V to +3.75V

+15V to +75V

Lead Temperature (Soldering,

<

10sec.) 300˚C

ESD Tolerance, Human Body Model 2kV

Electrical Characteristics

(See Figure 3 for Test Circuit)
Unless otherwise noted: VCC= +80V, VBB= +12V, CL= 8pF, TC= 50˚C.
DC Tests: V
AC Tests: Output = 40VPP(25V - 65V) at 1MHz

Symbol Spec Parameter Conditions Min Typ Max Units

I

CC

I

BB

V

OUT

A

V

∆A

V

LE Linearity Error Note 4, 5, No AC Input Signal 5 %
t

R

t

F

OS Overshoot Note 6 5 %

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

the 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
Note 6: Input from signal generator: t

= +2.25VDC

IN

Supply Current Per Channel, No Input Signal, No

Output Load

812mA

Bias Current All three Channels 15 25 mA
DC Output Voltage No AC Input Signal, VIN= 1.25V 62 65 68 V
DC Voltage Gain No AC Input Signal -18 -20 -22
Gain Matching Note 4, No AC Input Signal 1.0 dB

Rise Time Note 6, 10% to 90% 9.5 nS
Fall Time Note 6, 90% to 10% 10.5 nS

= 1.0 volts to Vin= 3.5 volts.

in

R,tF

<

1nS.

DC

AC Test Circuit

FIGURE 3. Test Circuit (One Channel)

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DS200006-3

Typical Performance Characteristics

(VCC= +80VDC,VBB= +12VDC,CL= +8pF, V

Figure 9: V

out

vs V

in

= 40VPP(25-65V), Test Circuit - Figure 3 unless otherwise specified.

OUT

DS200006-4

LM2469

DS200006-7

Figure 10: Power Dissipation vs Frequency

DS200006-5

Figure 11: Speed vs Temperature

DS200006-6

Figure 13: LM2469 Pulse Response

DS200006-8

Figure 12: Speed vs Offset

DS200006-9

Figure 14: Speed vs Load Capacitance

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THEORY OF OPERATION

The LM2469 is a high voltage monolithic three channel CRT

LM2469

driver suitable for color monitor applications. The LM2469
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 LM2469 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 amplifier from the
capacitive load on the output of the amplifier, decreasing the
sensitivity of the device to changes in load capacitance. Q6
provides biasing to the output emitter follower stage to re­duce crossover distortion at low signal levels.

Figure 3 shows a typical test circuit for evaluation of the
LM2469. This circuit is designed to allow testing of the
LM2469 in a 50Ω environment without the use of an expen­sive FET probe. In this test circuit, two low inductance resis­tors in series totalling 4.95KΩ form a 200:1 wideband, low
capacitance probe when connected to a 50Ω load (such as
50Ω oscilloscope input). The input signal from the generator
is AC coupled to the base of Q5.

APPLICATION HINTS

INTRODUCTION

National Semiconductor (NSC) is committed to provide ap­plication information that assists our customers in obtaining
the best performance possible from our products. The fol­lowing information is provided in order to support this com­mitment. The reader should be awarethat theoptimization 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 com­ponent value changes might be required in order to optimize
performance in a given application. The values shown inthis
document can be used as a starting point for evaluation
purposes. When working with high bandwidth circuits, good
layout practices are always critical to achieving maximum
performance.

supply and ground pins. A 0.1uF capacitor should be con­nected from the bias pin (V

) to the ground, as close as is

bb

practical to the part.

ARC PROTECTION

During normal CRToperation, internal arcing may occasion­ally 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 LM2469. This fast, high voltage, high energy pulse can
damage the LM2469 output stage. The application circuit
shown in Figure 4 is designed to help clamp the voltage at
the output of the LM2469 to a safe level. The clamp diodes,
D1 andD2, should have a fast transient response, high peak
current rating, low series impedance and low shunt capaci­tance. 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

and

cc

ground respectively. The cathode of D1 should be located
very close to aseparately decoupledbypass capacitor(C3 in
Figure 4). The ground connection of D2 and the decoupling
capacitor should be very close to the LM2469 ground. This
will significantlyreduce the high frequency voltagetransients
that the LM2469 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 LM2469 as
well as the voltage stress at the outputs of the device. R2
should be a 1/2W solid carbon type resistor. R1 can be a
1/4W metal or carbon film type resistor. Having large value
resistors for R1 and R2 would be desirable, but has the
effect of increasing rise and fall times. Inductor L1 is critical
to reduce the initial high frequency voltage levels that the
LM2469 would be subjected to. The inductor will not only
help protect the device, but will also help optimize rise and
fall times as well as minimizeEMI. For proper arc protection,
it is important to not omit any of the arc protection compo­nents shown in Figure 4.

IMPORTANT INFORMATION

The LM2469 performance is targeted for the VGA (640 x

480) to XGA (1024 x 768, 70Hz refresh) resolution market. It
is designed to be a replacement for discrete CRT drivers.
The application circuits shown in this document to optimize
performance and to protect against damage from CRT arc­over are designed specifically for the LM2469. If another
member of the LM246X family is used, please refer to its
datasheet.

POWER SUPPLY BYPASS

Since the LM2469 isa widebandwith amplifier, properpower
supply bypassing is critical for optimum performance. Im­proper power supply bypassing can result in large over­shoot, ringing or oscillation. A 0.1uF capacitor should be
connected from the supply pin, V

, to ground, as close to

CC

the supply and ground pins as is practical. Additionally, a
10uF to 100uF electrolytic capacitor should be connected
from the supply pin to ground. The electrolytic capacitor
should also be placed reasonably close to the LM2469’s

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DS200006-10

FIGURE 4. One Video Channel of the LM2469 with the

Recommended Arc Protection Circuit

OPTIMIZING TRANSIENT RESPONSE

Referring to

Figure 4

, 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. Increasing 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 # 78FR39K) were used for optimizing the
performance ofthe device in the NSC application board. The
values shown in

Figure 4

can be used as a good starting

point for the evaluation of the LM2469. Using variable resis-

APPLICATION HINTS (Continued)

tors for R1 will simplify finding the values needed for opti­mum performance in a given application. Once the optimum
value is determined, the variable resistors can be replaced
with fixed values.

Effect of Load Capacitance

Figure 14 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. Note that
the fall time stayed fairly constant while the rise time in­creased approximately 1.8% per pF.

Effect of Offset

Figure 12 shows the variation in rise and fall times when the
output offset of the device is varied from 40VDC to 50 VDC.
The rise time shows a maximum variation relative to the
center data point (45 VDC) of less than 1.3%. The fall time
shows a variation of about 3.9% relative to the center data
point.

LM2469

PC Board Layout Considerations

For optimum performance, an adequate ground plane, iso­lation between channels, good supply bypassing and the
minimization of unwanted feedback are necessary. Also, the
length of the signal traces from the preamplifier to the
LM2469 andfrom theLM2469 to the CRT cathode should be
as short as possible. 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 Analog Circuits″,
Butterworth-Heinemann, 1991.

Because of its high small signal bandwith, 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, andinput
wiring should be spaced as faras possiblefrom outputcircuit
wiring.

THERMAL CONSIDERATIONS

Figure 11 shows the performance of the LM2469 video
amplifiers in the testcircuit shown in Figure 3 as afunction of
case temperature. The figure shows that the rise time of the
LM2469 increases by approximately 9% as the case tem­perature increases from 30˚C to 100˚C. This corresponds to
a speed degradation of 1.3% for every 10˚C rise in case
temperature. The fall time degrades around 0.6% for every
10˚C in case temperature.

Figure 10 shows the maximum power dissipation of the
LM2469 vs.Frequency whenall three channels of thedevice
are driving an 8pF load with a 40 V

signal alternating one

p-p

pixel on,one pixel off. Thegraph assumes a 72% activetime
(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 application.
The designer should note that if the load capacitance is
increased, the AC component of the total power dissipation
will also increase.

The LM2469 case temperature must be maintained below
100˚C. If the maximum expected ambient temperature is
70˚C and the maximum power dissipation is 3.85W (from
Figure 10, 50MHz bandwith), then a maximum heat sink
thermal resistance can be calculated:

This example assumes a capacitive load of 8pF and no
resistive load.

TYPICAL APPLICATION

The typical application of the LM2469 is shown in Figure 5&

6. Used in conjunction with an LM126X and an LM2479/
2480 bias clamp, a complete 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 top 75MHz. Figure5&6aretheschematic for the
NSC demonstration board that can be used to evaluate the
LM126X/246X/2480 combination in a monitor.

NSC Demonstration Board

Figure 7shows therouting and component placement onthe
NSC LM126X/246X demonstration board. The schematic of
the board is shown in Figure5&6.This board provides a
good example of a layout that can be used as a guide for
future layouts. Note the location of the following compo­nents:

C16, C19

•

—VCCbypass capacitor, located very close to

pin 4 and the ground plane near the device.

C20

—VBBbypass capacitors, located close to pin 8 and

•

ground.

C46, C47, C48

•

V

clamp diodes. Very important for arc protection.

CC

—VCCbypass capacitors, near LM2469

The routing of the LM2469 video outputs to the CRT is very
critical to achieving optimum performance. Figure 8 shows
the routing and component placement from pin 3 of the
LM2469 to the blue cathode. Note that the components are
placed so that they almost line up from the output pin of the
LM2469 to 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 attached 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 ground plane that has a
short and direct path to the LM2469 ground pins. The cath­ode of D9 is connected to V

very close to decoupling

CC

capacitor C48 (see Figure 8), 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 LM2469 video outputs during an arc over
event. Lastly, notice that S3 is placed very close to the blue
cathode and is tied directly to the ground under the CRT
connector.

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APPLICATION HINTS (Continued)

LM2469

DS200006-29

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FIGURE 5. LM126X/246X Demonstration Board Schematic

APPLICATION HINTS (Continued)

LM2469

DS200006-30

FIGURE 6. LM126X/246X Demonstration Board Schematic (continued)

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APPLICATION HINTS (Continued)

LM2469

FIGURE 7. NSC LM126X/246X Demo Board Layout

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DS200006-17

APPLICATION HINTS (Continued)

LM2469

DS200006-18

FIGURE 8. Trace Routing and Component Placement for Blue Channel Video Output.

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Physical Dimensions inches (millimeters) unless otherwise noted

LM2469 Monolothic Triple 9nS High Gain CRT Driver

Note: Information contained in this data sheet is preliminary and may be subject to change without notice.

NS Package Number TA09A

Order Number LM2469TA

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