Datasheet LM2467TA Datasheet (NSC)

LM2467
Monolithic Triple 7.5 ns CRT Driver

LM2467 Monolithic Triple 7.5 ns CRT Driver

October 2000

General Description

The LM2467 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, limited only by the package’s power dissipation.

The IC is packaged in an industry standard 9-lead TO-220
molded plastic power package. See Thermal Considerations
section.

Schematic and Connection Diagrams

Features

n Higher gain to match LM126X CMOS preamplifiers
n 0V to 3.75V input range
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

Applications

n 1024 x 768 displays up to 85 Hz refresh
n Pixel clock frequencies up to 95 MHz
n Monitors using video blanking

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Note: TabisatGND

Top View

Order Number LM2467T

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FIGURE 1. Simplified Schematic Diagram

(One Channel)

© 2000 National Semiconductor Corporation DS200078 www.national.com

Absolute Maximum Ratings (Notes 1, 3)

If Military/Aerospace specified devices are required,

LM2467

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

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

) +90V

CC

) +16V

BB

) 0V to 4.5V

IN

) −65˚C to +150˚C

STG

Lead Temperature

<

(Soldering,

10 sec.) 300˚C

ESD Tolerance, Human Body Model 2 kV

Machine Model 250V

Operating Ranges (Note 2)

V

CC

V

BB

V

IN

V

OUT

+60V to +85V

+8V to +15V

+0V to +3.75V

+15V to +75V
Case Temperature −20˚C to +100˚C
Do not operate the part without a heat sink.

Electrical Characteristics

(See

Figure 2

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

Symbol Parameter Conditions

I

CC

I

BB

V

OUT

A

V

∆A

V

LE Linearity Error (Notes 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

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

for Test Circuit)

= 2.25VDC

IN

LM2467

Min Typical Max

Supply Current All Three Channels, No Input Signal,

No Output Load

30 mA

Bias Current All Three Channels 18 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% 7.5 ns
Fall Time (Note 6), 90% to 10% 8 ns

= 1.0V to VIN= 3.5V.

IN

r,tf

<

1 ns.

Units

DC

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AC Test Circuit

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Note: 8 pF load includes parasitic capacitance.

FIGURE 2. Test Circuit (One Channel)

Figure 2

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.

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

LM2467

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Typical Performance Characteristics (V

(25V−65V), Test Circuit -

LM2467

Figure 2

unless otherwise specified)

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

CC

OUT

=40V

PP

FIGURE 3. V

OUT

vs V

IN

FIGURE 4. Speed vs Temp.

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FIGURE 6. Power Dissipation vs Frequency

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FIGURE 7. Speed vs Offset

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FIGURE 5. LM2467 Pulse Response

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FIGURE 8. Speed vs Load Capacitance

Theory of Operation

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
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 cross­over distortion at low signal levels.

Figure 2

LM2467. This circuit is designed to allow testing of the
LM2467 in a 50Ω environment without the use of an expen­sive FET probe. In this test circuit, the two 4.95kΩ resistors
form a 200:1 wideband, low capacitance probe when con­nected 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.

shows a typical test circuit for evaluation of the

Figure 1

. The

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 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 com­ponent 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 per­formance.

ARC PROTECTION

During normal CRT operation, 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 LM2467. This fast, high voltage, high energy pulse can
damage the LM2467 output stage. The application circuit
shown in
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 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
ground respectively. The cathode of D1 should be located
very close to a separately decoupled bypass capacitor (C3 in

Figure 9

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
should be a
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
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 compo­nents shown in

Figure 9

). The ground connection of D2 and the decoupling

is designed to help clamp the voltage at

CC

1

⁄2W solid carbon type resistor. R1 can be a1⁄4W

Figure 9

.

and

LM2467

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 ar­cover 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 over­shoot, ringing or oscillation. 0.1 µF capacitors should be
connected from the supply pins, V
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.

and VBB, to ground, as

CC

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Application Hints (Continued)

LM2467

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

OPTIMIZING TRANSIENT RESPONSE

Referring to
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
performance of the device in the NSC application board. The
values shown in
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.

EFFECT OF LOAD CAPACITANCE

Figure 8

the speed of the device. This demonstrates the importance
of knowing the load capacitance in the application.

EFFECT OF OFFSET

Figure 7

output offset of the device is varied from 40 to 50 V
rise time shows a maximum variation relative to the center
data point (45 V
variation of less than 5% relative to the center data point.

THERMAL CONSIDERATIONS

Figure 4

circuit shown in
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 degrada­tion of 2% for every 10˚C rise in case temperature.There is a
negligible change in fall time vs. temperature in the test
circuit.

Figure 6

LM2467 vs. Frequency when all three channels of the device
are driving an 8 pF load with a 40 V
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-

Figure 9

, there are three components (R1, R2

#

78FR--k) were used for optimizing the

Figure 10

and

Figure 11

can be used as a

shows the effect of increased load capacitance on

shows the variation in rise and fall times when the

) less than 5%. The fall time shows a

DC

shows the performance of the LM2467 in the test

Figure 2

as a function of case temperature.

shows the maximum power dissipation of the

alternating one pixel

p-p

DC

. The

DS200078-10

cation. The designer should note that if the load capacitance
is increased the AC component of the total power dissipation
will also increase.

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
and

Figure 11

. Used in conjunction with an LM1267, a com-

Figure 10

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.
and

Figure 11

are the schematic for the NSC demonstration

Figure 10

board that can be used to evaluate the LM1267/2467 com­bination in a monitor.

PC BOARD LAYOUT CONSIDERATIONS

For optimum performance, an adequate ground plane, iso­lation between channels, good supply bypassing and mini­mizing 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:

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.

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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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—VCCbypass capacitor, located very close to pin 4

•

and ground pins
C20—VBBbypass capacitors, located close to pin 8 and

•

ground
C46, C47, C48— VCCbypass capacitors, near LM2467

•

and V

The routing of the LM2467 outputs to the CRT is very critical
to achieving optimum performance.
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

clamp diodes. Very important for arc protection.

CC

Figure 13

shows the

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 the ground plane that has a short
and direct path to the LM2467 ground pins. The cathode of
D9 is connected to V
C19 (see
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.

Figure 13

very close to decoupling capacitor

CC

) which is connected to the same section

LM2467

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Application Hints (Continued)

LM2467

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FIGURE 10. LM126X/LM246X Demonstration Board Schematic

Application Hints (Continued)

LM2467

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FIGURE 11. LM126X/LM246X Demonstration Board Schematic (continued)

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Application Hints (Continued)

LM2467

FIGURE 12. LM126X/LM246X Demo Board Layout

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Application Hints (Continued)

LM2467

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

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Physical Dimensions inches (millimeters) unless otherwise noted

LM2467 Monolithic Triple 7.5 ns CRT Driver

CONTROLLING DIMENSION IS INCH
VALUES IN [ ] ARE MILLIMETERS

NS Package Number TA09A

Order Number LM2467TA

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