NSC LM2433

220V Monolithic Single Channel 16 MHz EDTV CRT
General Description
The LM2433 is a single channel high voltage CRT driver
circuit designed for use in Rear-Projection and Direct-View
EDTV applications. The IC contains a high input impedance,
wide band amplifier which can be DC coupled to a cathode
of a CRT. The amplifier has its gain internally set to −53 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 a staggered 7-lead TO-220 molded
plastic power package designed specifically to meet high
voltage spacing requirements. See the section “Power Dissipation and Heatsink Calculation” for more information.
n For Rear-Projection and Direct-View DC coupled CRT
applications using EDTV formats
n Compatible with RGB video processors with IK feedback
for automatic cathode calibration
Pinout Diagram
Schematic Diagram
16 MHz bandwith at 110VPP output swing
0V to 4V input range
Greater than 110VPP output swing capability
IK Current Output (pin 5) for IK feedback systems
Emitter (pin 6) access to increase voltage gain
Note: Tab is at GND.
Top View
Order Number LM2433TE
FIGURE 1. Simplified Connection and Pinout Diagram
FIGURE 2. Simplified Schematic Diagram
© 2005 National Semiconductor Corporation
LM2433 220V Monolithic Single Channel 16 MHz EDTV CRT Driver
November 2005
Absolute Maximum Ratings
Operating Ranges (Note 2)
(Notes 1,
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
+7V to +13V
0V to +4.25V
Supply Voltage (VCC)
Bias Voltage (VBB)
-0.5V to VBB+0.5V
IK Voltage (VIK)
Input Voltage (VIN)
0V to VBB+1V
+45V to VCC–5V
Case Temperature
-0.5V to +16V
Storage Temperature Range (TSTG)
+130V to +230V
See Figure 10. Derate power for
TC above 110˚C.
Do not operate the part without a heat sink.
-65˚C to +150˚C
Lead Temperature
(Soldering, < 10 sec.)
ESD Tolerance,
Human Body Model
2 kV
Machine Model
Junction Temperature
θJC (typ)
Electrical Characteristics (See Figure 3 for Test Circuit)
Unless otherwise noted: VCC = +220V, VBB = +12V, CL = 10 pF, TC = 40˚C, pin 6 floating (REM = open).
DC Tests: VIN = 2.75VDC
AC Tests: Output = 110VPP (80V - 190V) at 1 MHz
Supply Current
Bias Current
DC Output Voltage
DC Output Voltage
No AC Input Signal, VIN = 1.25VDC
DC Voltage Gain
No AC Input Signal
Linearity Error
(Note 4), No AC Input Signal
Rise Time
(Note 5), 10% to 90%
(Note 5)
Fall Time
(Note 5), 90% to 10%
(Note 5)
IK Current Output Error
(Notes 6, 7), VCC = 210V, VOUT =
No AC Input Signal, No Output Load
No AC Input Signal, VIN = 2.75VDC
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. Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. 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
Note 3: All voltages are measured with respect to GND, unless otherwise specified.
Note 4: Linearity Error is the variation in DC gain from VIN = 1.15V to VIN = 4.35V.
Note 5: Input from signal generator: tr, tf < 2 ns. Slower inputs to the LM2433 will change the transient response and reduce power dissipation.
Note 6: IKERROR = IK – IOUT, where IK is the IK current output from pin 5 (IK) and IOUT is the cathode current into pin 2 (VOUT). IK can be measured with a precision
ammeter or calculated by measuring VIK across a known resistor value between pin 5 and GND. Refer to the “Cathode Current Output for IK Feedback Systems”
section for more information.
Note 7: Refer to the RGB Video Processor data sheet for IK leakage compensation, feedback operation, and adjustment range information.
AC Test Circuit
Note: 10pF load includes parasitic capacitance.
FIGURE 3. Test Circuit
Figure 3 shows a typical test circuit for evaluation of the LM2433. This circuit was designed to test the transient response of the
LM2433 in a 50Ω environment without the use of an expensive FET probe. On the input side, a 50Ω pulse generator output can
be AC coupled and biased with an external supply via the VADJ input. On the output side, the two 4990Ω resistors form a 400:1
divider with the 50Ω resistor and the oscilloscope. A test point can be included for easy use of an oscilloscope probe. A
compensation capacitor can be used to compensate the network to achieve a flat frequency response.
Typical Performance Characteristics (VCC = +220V, VBB = +12V, CL = 10 pF, VOUT = 110VPP (80V
− 190V), pin 6 floating, Test Circuit - Figure 3, unless otherwise specified)
FIGURE 7. Speed vs Offset
FIGURE 5. LM2433 Pulse Response
FIGURE 8. Speed vs Case Temperature
FIGURE 6. Bandwidth
FIGURE 9. Power Dissipation vs Frequency
FIGURE 10. Power Derating Curve
FIGURE 11. Cathode Pulse Response
Typical Performance Characteristics (VCC = +220V, VBB = +12V, CL = 10 pF, VOUT = 110VPP (80V
− 190V), pin 6 floating, Test Circuit - Figure 3, unless otherwise specified) (Continued)
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.
Theory of Operation
The LM2433 is a high voltage monolithic single channel CRT
driver suitable for EDTV applications. The LM2433 typically
operates with +220V and +12V power supplies. The part is
housed in a staggered 7-lead TO-220 molded plastic power
The circuit diagram of the LM2433 is shown in Figure 2. 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 −53. 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.
The LM2433 performance is targeted for the EDTV market.
The application circuits shown in this document to optimize
performance and to protect against damage from CRT arcover are designed specifically for the LM2433. If another
member of NSC’s DTV CRT Driver family is used, please
refer to its data sheet.
Since the LM2433 is a wide bandwidth amplifier, proper
power supply bypassing is critical for optimum performance
and for robustness against arcover. Improper power supply
bypassing can result in large overshoot, ringing or oscillation, and even arcover failure. 0.1 µF capacitors should be
connected from the supply pins, VCC and VBB, to ground
using very short traces. Additionally, a 10 µF or larger electrolytic capacitor should be connected from both supply pins
to ground reasonably close to the LM2433.
The emitter of Q1 is accessible via pin 6 and enables a
higher voltage gain, if needed. The gain improvement can be
helpful in applications where a channel’s gain needs to be
increased to compensate for a limited preamplifier drive
register adjustment. An external resistor, REM, can be connected between pin 6 and GND, so it’s in parallel with
internal emitter resistor, R2. A properly chosen resistor will
decrease the total emitter resistance to produce a higher
voltage gain. Figure 4 shows typical transfer curves for
various values of REM. To determine the value of REM for the
new voltage gain, AV’, use the following approximation:
REM = 10.6 / ( |AV’| – 53 ), where REM is in kΩ. If the
application does not require higher gain, then pin 6 should
be left floating.
The LM2433 has an IK current output (pin 5) that produces a
replica of the actual cathode current into VOUT (pin 2). The IK
output pin is internally connected to the collector of Q4. The
IK output can be connected through an interface circuit to a
RGB video processor with IK feedback for automatic cathode calibration. Note: During the non-blanking period, video
current levels can be as high as several mA, which is much
higher than the reference currents (in µA range) produced
during the IK measurement interval. These high currents
have the potential to produce large voltages at the IK output
pin. To avoid damage to Q4, the IK output pin should be
protected with a clamp diode to VBB so it’s voltage, VIK, does
not exceed +16V (VIKMAX). Please see the section “Cathode
Current Output for IK Feedback Systems” for more information on the usage and protection of the IK output. If the IK
output is not used in the application, it should be connected
to the same ground as pin 3 (GND).
During normal CRT operation, internal arcing may occasionally occur. This fast, high voltage, high energy pulse can
damage the LM2433 output stage since it is DC coupled to
the cathode. In a DC coupled application, an external spark
gap with an arcover voltage rating of 200 to 300VDC on the
cathode is NOT recommended. The internal CRT socket
spark gap (1 to 2 kVDC rating) can sufficiently reduce the
initial arcover voltage seen at the cathode. The output circuit
shown in Figure 12 is designed to help clamp the voltage at
the output of the LM2433 to a safe level during an arcover.
External arc protection clamp diodes, D1 and D2, should
have a fast transient response, high peak current rating, low
series impedance and low shunt capacitance. 1SS83 or
equivalent diodes like BAV21 are recommended. D1 and D2
should have short, low impedance connections to VCC and
ground respectively. The cathode of D1 should have a very
short connection to a separate VCC bypass capacitor, C3.
The ground connection of D2 and the C3 should have a
short, direct path to ground. This will significantly reduce the
high frequency voltage transients that the LM2433 would be
subjected to during an arcover.
Resistor R2, which limits the arcover current that is seen by
the diodes, should be a 1⁄2W solid carbon type resistor. R1
limits the current into the LM2433 as well as the voltage
stress at the outputs of the device and can be a 1⁄4W 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 LM2433 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 12.
Application Hints
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
Application Hints
FIGURE 12. Recommended Application Circuit
A Practical Approach to Power Dissipation
Figure 7 shows the variation in rise and fall times when the
DC offset of the 110VPP output swing is varied between
120V and 150VDC. The rise time and fall time show a maximum variation of about 6% relative to the center data point
(135VDC), which is a relatively small variation in speed over
the 30V DC offset range.
The power curve (Figure 9) mentioned previously shows the
LM2433 power dissipation for square wave frequencies
ranging from 1 to 50 MHz at 110VPP swing. In practice, it is
uncommon for a TV to display average frequency content
over the entire picture exceeding 20 MHz. Therefore, it is
important to establish the worst-case picture condition under
normal viewing to give a realistic maximum power dissipation for the LM2433. Here is one approach:
An EDTV signal generator pattern that yields a practical
worst-case picture condition is a “multi-burst” pattern that
consists of a 1-to-30 MHz sine wave sweep over each of the
active lines. The power dissipated by the LM2433 as a result
of this picture condition can be approximated by taking the
average of the power between 1 to 30 MHz in Figure 9. This
average is 5.1W. Because a square wave input was used to
generate this power curve, a sine wave would cause the
LM2433 to dissipate slightly less power, say 5.0W. This is
one common way to determine a practical figure for maximum power dissipation. It is the system designer’s responsibility to establish the worst-case picture condition for his
particular application and measure dissipation under that
condition to choose a proper heatsink.
Heatsink Calculation Example
Once the maximum dissipation is known, Figure 10 can be
used to determine the heatsink requirement for the LM2433.
If the 1-to-30 MHz multi-burst test described previously is
assumed to be worst-case picture condition that yields maximum dissipation, then the LM2433 will dissipate about 5.0W.
The power derating curve shows that the maximum allowed
case temperature is 127.5˚C when 5.0W is dissipated. If the
maximum expected ambient temperature is 65˚C, then the
maximum thermal resistance from device case-to-air (θCA)
can be calculated:
Figure 8 shows the performance of the LM2433 as a function
of case temperature. The figure shows that the rise and fall
times of the LM2433 increase by approximately 4.5% and
6.5%, respectively, as the case temperature increases from
40˚C to 90˚C. This corresponds to a speed degradation of
about 0.9% and 1.3% for every 10˚C rise in case temperature, which is very stable performance over the temperature
Worst-Case Power Dissipation
Figure 9 shows the maximum power dissipation of the
LM2433 vs. square wave frequency when the device uses
VCC of 220V and is driving a 10 pF load with 110VPP swing
alternating one pixel on, one pixel off signal. Note that the
frequency range shown in the power dissipation figure is
one-half the actual pixel frequency. The graph assumes 80%
active time (device operating at the specified frequency),
which is typical in an EDTV application. The other 20% of the
time the device is assumed to be sitting at the black level
(190V in this case). Under this worst-case condition, the
maximum power dissipated by the LM2433 is about 6.8W at
around 40 MHz. It is important to note that this power dissipation is a result of a high frequency square wave input,
which is unrealistic in practical TV applications. The bandwidth of the input source used to drive the LM2433 was over
300 MHz. Using a RGB video processor or preamplifier with
less bandwidth will cause the LM2433 to dissipate less
power than shown in Figure 9 at the same conditions.
θCA = (127.5˚C – 65˚C) / 5.0W = 12.5˚C/W.
θCS is the thermal resistance of the thermal compound at the
case-to-heatsink interface and θSA is the thermal resistance
of the heatsink at the rated conditions.
This example assumes a capacitive load of 10 pF and no
resistive load. The designer should note that if the VCC
supply voltage, output swing, input bandwidth, or load capacitance is increased, then the power dissipation will also
Application Hints
back circuit in detail. For more information, please refer to
the RGB processor data sheet or contact your local National
Semiconductor Sales Office with your specific application
Tips for Reducing Power Dissipation
The following methods can be used to reduce the power
dissipated by the LM2433 in order to optimize heatsink size
and cost:
• Use a lower VCC supply voltage while maintaining sufficient operating range for cutoff, brightness, and drive
• Lower the maximum VPP swing while maintaining acceptable picture contrast and brightness.
• Reduce the input bandwidth to the LM2433 while maintaining acceptable picture performance.
• Minimize capacitive load on the LM2433 output by using
good PCB layout practices.
Feedback Topologies
RGB processors that use voltage feedback require the
LM2433 IK current to be converted to voltage via a resistor
(RIK) to ground. This IK voltage, VIK, will be fed back to the IK
input of the RGB processor through an interface circuit,
which will be AC or DC coupled depending on the processor’s IK input requirement. For proper feedback operation,
some processors may require an emitter follower to isolate
the IK input from the high impedance of the resistor. During
the closed-loop IK measurement interval, the IK input voltage will be sampled and compared with the processor’s
internal reference voltage to automatically calibrate the video
levels for the next field. The value of RIK is crucial, since it
establishes the IK voltage and consequently, the operating
point of the CRT. Once a stable operating point is established with a properly chosen resistor, this point can be
fine-tuned using the adjustment range of the processor’s
RGB cut-off and/or gain controls via the I2C-bus. After the IK
measurement interval (usually at the end of blanking), normal video will resume and high currents will flow out of the IK
output. These high video currents will produce large IK voltages across the resistor that can exceed the maximum
voltage rating for VIK. Therefore, it is recommended to use a
high-speed diode (DPROT) to clamp the LM2433 IK output to
a safe level (preferably VBB or a lower supply). If a zener
diode is used instead, it may be necessary for the RGB
processor to have IK leakage compensation for the leakage
current attributed to the zener. Lastly, it is possible to use a
single RIK resistor to set the IK voltage for all three LM2433s.
See a simplified voltage feedback interface circuit in Figure
Referring to Figure 12, 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 # 78FR_ _k) were used for optimizing the
performance of the device in the NSC application board. The
values shown in Figure 15 can be used as a good starting
point for the evaluation of the LM2433. Using a variable
resistor for R1 will simplify finding the value needed for
optimum performance in a given application. Once the optimum value is determined, the variable resistor can be replaced with a fixed value.
Figure 11 shows a typical cathode pulse response with an
output swing of 110VPP using a RGB video processor that
provides input speeds with 12 ns rise and fall times. Note:
The RGB processor’s sharpness feature adds emphasis
(pre-shoot and over-shoot) to the rising and falling edges of
the input pulse, which consequently adds emphasis to the
cathode pulse response.
IK Feedback Systems
IK feedback was developed to accurately bias the CRT and
continuously calibrate it to the correct cut-off and/or drive
levels over the useful life of the CRT. RGB video processors
that use IK feedback to automatically adjust only cut-off, or
black level, are realized by a 1-point calibration system. A
few trade names for this system are Auto Kine Bias (AKB)
and Black Current Stabilization (BCS). RGB processors that
can automatically adjust both cut-off and drive, or white
level, are realized by a 2-point calibration system. This is
commonly known as Continuous Cathode Calibration
(CCC). For convenience, some 2-point RGB processors may
be programmed to 1-point operation if drive calibration is not
required. The LM2433 is compatible with both 1- and 2-point
To be compatible with various RGB processors, an interface
circuit may be needed in the feedback path between the
LM2433 IK output and the processor’s IK input. This feedback circuit depends on the RGB processor and feedback
topology (voltage or current) used. Because each processor
has its own IK input signal and topology requirements, it is
outside the scope of this data sheet to describe each feedwww.national.com
FIGURE 13. Simplified IK Interface for Voltage
Feedback Systems
RGB processors that use current feedback do not require
voltage conversion. The LM2433 IK current can be fed back
directly to the IK input of the RGB processor, although some
protection circuitry will be needed to protect the RGB processor and LM2433. During the closed-loop IK measurement interval, the voltage of the RGB processor’s IK pin will
be internally clamped, and the IK current will be sampled and
compared with the processor’s internal reference current to
calibrate the video levels. The operating point of the CRT
can be fine-tuned using the adjustment range of the processor’s RGB cut-off and/or gain controls via the I2C-bus. When
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 LM2433 and
from the LM2433 to the CRT cathode should be as short as
possible. The following references are recommended:
normal video resumes, a protection element should shunt
high video current away from the IK input of the RGB processor. Since the processor’s IK pin is not clamped during
normal video, VIK of the LM2433 must not exceed +16V
(VIKMAX). A properly chosen high speed, low-leakage zener
diode (DPROT) can be used to protect both the RGB processor input and LM2433 IK output in this case. Again, it may be
necessary for the RGB processor to have IK leakage compensation for the leakage current attributed to the zener. See
a simplified current feedback interface circuit in Figure 14.
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 TV 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
The high bandwidth, large swing capability, and simple application make the LM2433 ideal for Rear-Projection and
Direct-View EDTV CRT applications. The IK output can be
made compatible with any RGB video processor with IK
feedback. If the IK output is not used in the application, it
should be connected to the same ground as pin 3 (GND).
See the section “Cathode Current Output for IK Feedback
Systems” for more information.
FIGURE 14. Simplified IK Interface for Current
Feedback Systems
Figure 15 and Figure 16 show the schematic and PCB layout
for the NSC demonstration neck board for a typical RearProjection EDTV application with IK feedback. This single
channel neck board could be used for all three channels,
since each neck board receives video-related signals directly
from the RGB mainboard. The power supplies are daisychained between each channel using inboard and outboard
connectors J6 and J7. This board provides a good example
of a layout that can be used as a guide for future layouts.
Samples of the NSC demonstration neck board are available
upon request to your local National Semiconductor Sales
Input Video Interface
On the RGB mainboard, the video output of the RGB processor is buffered with a PNP transistor to drive the video
through flat cabling to the NSC neck board. The cabling from
the mainboard plugs into the neck board at connector J8 to
supply it with video, IK, GND, and other signals. Between the
video input (pin 3) of J8 and VIN (pin 7) of the LM2433 is
another buffer stage consisting of two NPN transistors. Both
NPN transistors drop the video levels from the preceding
PNP buffer by a total of two VBE. This shifts the nominal input
black level such that the LM2433 output (or cathode) black
level voltage is near the nominal cut-off voltage of the CRT.
The overall voltage shift from the processor output to the
LM2433 input is one VBE drop. Note: The same video level
shifting could have been accomplished using one NPN
buffer on the RGB mainboard to drive the processor’s video
output through cabling directly to the LM2433 input. However, it was decided to preserve the TV’s original RGB
mainboard circuitry (the PNP buffer) and use two NPN transistors on the neck board.
LM2433 IK Output and Protection Requirements
The LM2433 IK output sources a copy of the actual cathode
current to the interface circuit during the closed-loop IK
measurement interval and during normal video when the IK
feedback loop is opened. Because the cathode current during normal video is much higher than the low current being
measured during the measurement interval, VIK may exceed
it’s maximum rating. To protect and prevent improper operation of the LM2433, VIK must be maintained within the range
specified in the Section Operating Ranges .
For voltage feedback topologies, it is recommended to use a
high-speed diode to clamp the IK voltage to VBB or a lower
supply during normal video. A small series resistor (RD in
Figure 13) can be placed at the IK pin to limit the current
through the diode when clamping. See the NSC Demonstration Board for an example. For current feedback topologies,
it is recommended to use a high-speed, low-leakage zener
diode to clamp VIK to a properly chosen zener voltage and
shunt the high video current away from the RGB processor’s
IK input. The zener voltage should be higher than the clamping voltage of the processor’s IK pin and lower than the
maximum voltage rating of either the processor’s IK pin or
LM2433 VIK, whichever is the less.
In a Direct-View TV application with a single neck PCB, it is
possible for the three LM2433 IK outputs to share the one
feedback circuit and protection diode by connecting the IK
pins together on the neck PCB. This will reduce component
count. In a Rear-Projection TV application with three neck
PCBs, the IK pins can be connected on the central neck PCB
or the RGB processor mainboard through cabling. This way,
they can share the interface circuit to feed back the IK
voltage or current signal to the RGB processor. However,
each LM2433 IK output should have its own protection diode
on its PCB.
Application Hints
Application Hints
(except for replacing the original neck boards). Therefore,
the video interface and IK feedback circuits are designed to
be compatible with those original TV circuits. Referring to
Figure 15, the LM2433 IK output (pin 5) is connected to
protection circuitry before the IK current signal is routed to
pin 4 of connector J8. Diode D1 protects the LM2433 IK pin
from excessive voltage during normal video by clamping to
the VBB supply. Diode D2 isolates the IK output from the
other channels during the active IK measurement interval.
Resistors R17 and R12 limit the current through D1 and D2,
and C12 is used for filtering. From connector J8, the IK
current signal is passed through cabling and combined with
the other two IK signals on the RGB mainboard.
The input stage from the RGB processor to the LM2433 will
be determined by the system designer for his specific application. The input stage required depends mainly on the
following system parameters:
• Nominal CRT cut-off voltage
• Nominal black level output voltage of the RGB processor
• VCC & VBB supply voltages of the LM2433
Once the nominal black level input to the LM2433 establishes a cathode black level near the CRT cut-off voltage, it
can be fine-tuned using the processor’s cut-off adjustment
and calibrated automatically using the IK feedback system, if
applicable. Lastly, some RGB processor video outputs cannot adequately drive the capacitive load introduced by the
cabling between the RGB mainboard and neck boards. To
prevent loading the processor’s output, a NPN or PNP buffer
stage can be applied close to the output on the mainboard to
sufficiently drive the video signal through cabling to the neck
board. It is important to bias the buffer stage(s) properly to
obtain optimal video performance and maintain the full video
adjustment range of the RGB processor.
Video Output and Arc Protection
The routing of the LM2433 output to the CRT is very critical
to achieve optimal video performance and robustness
against arcover. Figure 16 shows the routing and component
placement from VOUT (pin 2) of the LM2433 to the cathode
pin of the CRT socket. The components are placed so that
there is a short, direct path from the LM2433 output to the
cathode. This is done to reduce the PCB parasitic capacitance on the LM2433 output and minimize EMI. Note also
that L3, D3, D4, and R6 are placed to minimize the size of
the video nodes that they are attached to. This enhances the
effectiveness of the arc protection diodes. The anode of
protection diode D3 is connected directly to a section of the
ground plane that has a short, direct path to the LM2433
ground plane. The cathode of D4 is connected to VCC very
close to decoupling capacitor C7, which is connected to the
same section of the ground plane as D3. The diode placement and routing is very important to shunt arcover current
away from the output and minimize the voltage stress on the
LM2433. The internal CRT socket spark gap will serve to
significantly reduce the initial arcover voltage seen at the
cathode. The DAG connector should be connected to CRT
ground for arc return current.
IK Feedback Circuit
The NSC demonstration neck board was made so that no
modifications to the existing TV circuitry were necessary
Note: The following paragraph describes circuitry that is not
part of the NSC demonstration neck board. The RGB processor, which operates with a voltage feedback IK topology,
uses a single “IK resistor” on the RGB mainboard to convert
all three IK currents into a voltage signal. The IK voltage
signal is then buffered through a PNP transistor before it is
filtered and AC coupled to the RGB processor’s IK input.
This is one implementation of the IK feedback circuit based
on this TV’s specific RGB processor. The system designer
should refer to the RGB processor data sheet to determine
the appropriate feedback circuit implementation for his application.
Supply Decoupling
Note the location of the following components:
• C5 — VCC bypass capacitor with short traces to the VCC
and GND pins of LM2433.
• C7 — VCC bypass capacitor with short traces to the VCC
arc protection diode and ground. This capacitor is very
important for arc protection.
• C9 — VBB bypass capacitor with short traces to the VBB
and GND pins.
• C10 and C11 — VCC and VBB electrolytic capacitors
placed near supply pins of LM2433.
Other Items
Connector J1 and switches JP2 & JP4 can be used to
bypass the TV’s internal 200V and 12V supplies and evaluate the LM2433 with external VCC and VBB supplies. Also,
this demonstration board uses medium-sized PCB holes to
accommodate socket pins, which function to allow for multiple insertions of the LM2433 in a convenient manner. To
benefit from the enhanced LM2433 package with thin leads,
the device should be secured with solder in small PCB holes
to optimize the metal-to-metal spacing between the leads.
Application Hints
FIGURE 15. LM2433 Demonstration Board Schematic
Application Hints
FIGURE 16. LM2433 Demonstration Board Layout
(slightly enlarged for more detail)
inches (millimeters) unless otherwise noted
NS Package Number TE07A
Order Number LM2433TE
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the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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(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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LM2433 220V Monolithic Single Channel 16 MHz EDTV CRT Driver
Physical Dimensions