Datasheet LM2406 Datasheet (NSC)

LM2406
Monolithic Triple 9 ns CRT Driver

LM2406 Monolithic 9 ns Triple CRT Driver

June 1995

General Description

The LM2406 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. The gain of
each channel is internally set at

b

14.5 and can drive CRT
capacitive loads as well as resistive loads presented by oth­er applications, limited only by the package’s power dissipa­tion.

The IC is packaged in an industry standard 11 lead TO-220
molded plastic power package. See thermal considerations
on page 4.

Schematic and Connection Diagrams

Features

Y

Output swing capability: 50 VPPfor V

Y

Pinout designed for easy PCB layout

Y

1V to 7V input range

Y

Stable with 0 pF –20 pF capacitive loads

Y

Convenient TO-220 staggered lead style package

40 V
30 V

PP
PP

for V
for V

CC
CC
CC

e

80

e

70

e

60

Applications

Y

CRT driver for 1024 x 768 (Non-interlaced) and SVGA
display resolution color monitors

Y

Pixel clock frequency up to 80 MHz

Note: Tab is at GND

TL/H/12327– 2

Top View

FIGURE 1. Simplified Schematic Diagram (One Channel)

TL/H/12327– 1

C

1995 National Semiconductor Corporation RRD-B30M115/Printed in U. S. A.

TL/H/12327

Absolute Maximum Ratings (Notes 1, 3)

a

BIAS

95V

a

16V

a

0.5V

Supply Voltage, V

Bias Voltage, V

Input Voltage, V

Storage Temperature Range, T

BIAS

IN

CC

STG

b

0.5V to V

b

65§Ctoa150§C

Lead Temperature (Soldering,k10 sec.) 300§C

ESD Tolerance 2 kV

Operating Range (Note 2)

V

CC

V

BIAS

V

IN

Case Temperature, T

Do not operate the part without a heat sink

CASE

a

60V toa85V

a

8V toa15V

a

1V toa7V

b

20§Ctoa100§C

Electrical Characteristics

Unless otherwise noted: V

CC

ea

80V, V

Symbol Parameter Conditions

I

V

t

t

A

CC

OUT

R

F

V

Supply Current (Per Channel) No Output Load 18 30 mA

Output Voltage No Input Signal 45 50 55 V

Rise Time 10%–90%, fe1 MHz 9 nS

Fall Time 90%–10%, fe1 MHz 9 nS

Voltage Gain

LE Linearity Error (Note 4) 8 %

DA

V

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: Linearity Error is defined as the variation in small signal gain from

Note 5: Calculated value from Voltage Gain test on each channel.

Note 6: Input signal, V

Gain Matching (Note 5) 1.0 dB

k

2 nS.

IN:tr,tf

BIAS

ea

12V, V

IN

ea

3.3V, C

e

8 pF, Outpute40 VPPat 1 MHz, T

L

Min Typical Max

b

13

a

30V toa70V output with a 100 mV AC, 10 kHz input signal.

LM2406

b

14.5

e

A

b

16 V/V

25§C.

Units

DC

AC Test Circuit

Note: 8 pF is total load including parasitic capacitance.

TL/H/12327– 3

FIGURE 2. Test Circuit (One Channel)

Figure 2

shows a typical test circuit for evaluation of the LM2406. This circuit is designed to allow testing of the LM2406 in a 50X
environment, such as a pulse generator, oscilloscope or network analyzer. The two series resistors at the output form a 100:1
voltage divider when connected to a 50X load.

2

FIGURE 3. V

OUT

vs V

IN

TL/H/12327– 4

FIGURE 4. Power Dissipation vs V

TL/H/12327– 5

CC

FIGURE 5. Large Signal Frequency Response

TL/H/12327– 6

Theory of Operation

The LM2406 is a high voltage monolithic triple CRT driver
suitable for VGA and SVGA display applications. The
LM2406 features
tion. The part is housed in the industry standard 11-lead
TO-220 molded plastic power package.

The circuit diagram of the LM2406 is shown in
and R2 provide a conversion of input voltage to current,
while Q2 acts as a common base or cascode amplifier stage
to drive the load resistor R1. Emitter followers Q3 and Q4
isolate the impedance of R1 from the capacitance of the
CRT cathode, and make the circuit relative insensitive to
load capacitance. The gain of this circuit is
and is fixed at
the collector time constant formed by the resistor R1 and

a

80V operation and low power dissipa-

Figure 1.

b

b

14.5. The bandwidth of the circuit is set by

R1/(R2llR3)

Q1

FIGURE 6. Pulse Response

associated capacitance of Q2, Q3, Q4 and stray layout ca­pacitance. Transistor Q6 and resistors R7 and R8 provide
biasing to the output emitter-follower stage to reduce cross­over distortion at low signal levels, while R3 provides a DC
bias offset to match the output level characteristics of the
preamplifier stage.

Figure 2

shows a typical test circuit for evaluation of the
LM2406. This circuit is designed to allow testing of the
LM2406 in a 50X environment, such as a pulse generator
and a scope, or a network analyzer. In this test circuit, two
resistors in series totaling 4.95 kX form a 100:1 wideband
low capacitance probe when connected to a 50X cable and
load. The input signal from the generator is AC coupled to
the base of Q5, while a DC bias of
base of Q2 (See

Figure 2

).

a

12V is applied to the

3

TL/H/12327– 7

Application Hints

POWER SUPPLY BYPASS

Since the LM2406 is a wide bandwidth amplifier, proper
power supply bypassing is critical for optimum performance.
Improper power supply bypassing can result in large over­shoot, ringing and oscillation. A 0.01 mF capacitor should be
connected as close to the supply pin, V
(preferably less than (/4
a10mF– 100 m F electrolytic capacitor should be connected
from the supply pin to ground. The electrolytic capacitor
should also be placed reasonably close to the LM2406’s
supply pin. A 0.1 mF capacitor should be connected from
the bias pin to ground, as close as is practical to the
LM2406.

The LM2406 is short circuit proof to momentary shorts to

k

ground (

ARC PROTECTION

During normal CRT operation, internal arcing may occasion­ally occur. Spark gaps of 200V –300V at the cathodes will
limit the maximum voltage, but to a value that is much high­er than allowable on the LM2406. This fast, high voltage,
high energy pulse can damage the LM2406 output stage.
The addition of clamp diodes D1 and D2 (as shown in

ure 7

LM2406 to a safe level. The clamp diodes should have a
fast transient response, high peak current rating, low series
impedance and low shunt capacitance. FDH400 or equiva­lent diodes are recommended. Resistor R2 in
the arcover current while R1 limits the current into the
LM2406 and reduces the power dissipation of the output
transistors when the output is stressed beyond the supply
voltage. Having large value resistors for R1 and R2 would
be desirable, but this has the effect of increasing rise and
fall times.

1 sec.).

) will help clamp the voltage at the output of the

from the supply pin). Additionally,

×

a

, as is practical

Figure 7

Fig-

limits

IMPROVING RISE AND FALL TIMES

Because of an emitter follower output stage, the rise and fall
times of the LM2406 are relatively insensitive to capacitive
loading. However, the series resistors R1 and R2 (see

ure 7

) will increase the rise and fall times when driving the

CRT’s cathode which appears as a capacitive load. The ca­pacitance at the cathode typically ranges from 8 pF –12 pF.

To improve the rise and fall times at the cathode, a small
inductor is often used in series with the output of the amplifi­er. The inductor L
cy response at the cathode, thus improving rise and fall
times The inductor value is empirically determined and is
dependent on the load. An inductor value of 0.1 mHisa
good starting value. Note that peaking the amplifier’s fre­quency response will increase the overshoot.

THERMAL CONSIDERATIONS

Power supply current increases as the input signal increas­es and consequently power dissipation also increases.

The LM2406 cannot be used without heat sinking. Typical
‘‘average’’ power dissipation with the device output voltage
at one half the supply voltage is 2.4W per channel for a total
dissipation of 7.2W package dissipation. Under white screen
conditions, i.e., 25V output, dissipation increases to 3.5W
per channel or 10.5W total. The LM2406 case temperature
must be maintained below 100
ambient temperature is 50
thermal resistance can be calculated:

This example assumes a typical CRT capacitive load and is
without a resistive load.

TYPICAL APPLICATION

A typical application of the LM2406 is shown in
Used in conjunction with an LM1207, a complete video
channel from monitor input to CRT cathode can be
achieved. Performance is satisfactory for all applications up
to 1024 x 768 non-interlaced.

e

R

th

in

Figure 7

P

100§Cb50§C

10.5W

peaks the amplifiers frequen-

C. If the maximum expected

§

C, then a maximum heat sink

§

e

4.76§C/W.

Fig-

Figure 8.

FIGURE 7. One Section of the LM2406 with Arc Protection and Peaking Inductor L

4

TL/H/12327– 8

P

Typical Applications

TL/H/12327– 9

FIGURE 8. Typical Application LM1207–LM2406

Note: Unmarked capacitors 0.1 mF

5

Physical Dimensions inches (millimeters)

LM2406 Monolithic 9 ns Triple CRT Driver

11-Lead Molded TO-220

Order Number LM2406

NS Package Number TA11B

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