LM2413T National Semiconductor, LM2413T Datasheet - Page 4

IC DRIVER MONOLITHIC TO-220-11

LM2413T

Manufacturer Part Number
LM2413T
Description
IC DRIVER MONOLITHIC TO-220-11
Manufacturer
National Semiconductor
Datasheet

Specifications of LM2413T

Display Type
CRT
Current - Supply
16mA
Voltage - Supply
60 V ~ 85 V
Operating Temperature
-20°C ~ 100°C
Mounting Type
Through Hole
Package / Case
TO-220-11 (Bent and Staggered Leads)
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
Interface
-
Configuration
-
Digits Or Characters
-
Other names
*LM2413T
www.national.com
Theory of Operation
The LM2413 is a high voltage monolithic three channel CRT
driver suitable for very high resolution display applications,
up to 1600 x 1200 at 70 Hz refresh rate. The LM2413 oper-
ates using 80V and 12V power supplies. The part is housed
in the industry standard 11-lead TO-220 molded plastic
power package.
The simplified circuit diagram of one channel of the LM2413
is shown in Figure 1 . A PNP emitter follower, Q5, provides in-
put buffering. This minimizes the current loading of the video
pre-amp. R9 is used to turn on Q5 when there is no input.
With Q5 turn on, Q1 will be almost completely off, minimizing
the current flow through Q1 and Q2. This will drive the output
stage near the V
with no inputs. R6 is a pull-up resistor for Q5 and also limits
the current flow through Q5. R3 and R2 are used to set the
current flow through Q1 and Q2. The ratio of R1 to R2 is
used to set the gain of the LM2413. R1, R2, and R3 are all
related when calculating the output voltage of the CRT
driver. R
Q2 are in a cascode configuration. Q1 is a low voltage and
very fast transistor. Q2 is a higher voltage transistor. The
cascode configuration gives the equivalent of a very fast and
high voltage transistor. The two output transistors, Q3 and
Q4, form a class B amplifier output stage. R4 and R5 are
used to limit the current through the output stage and set the
output impedance of the LM2413. Q6, along with R7 and R8
set the bias current through Q3 and Q4 when there is no
change in the signal level. This bias current minimizes the
crossover distortion of the output stage. With this bias cur-
rent the output stage now becomes a class AB amplifier with
a crossover distortion much lower than a class B amplifier.
Figure 2 shows a typical test circuit for evaluation of the
LM2413. Due to the very wide bandwidth of the LM2413, a
specially designed output circuit is used with the required se-
ries resistor and C
when evaluating the performance of the LM2413 in a 50
environment without the use of an expensive FET probe.
The combined resistors of 4950
voltage divider when connected to a 50 load. The input sig-
nal from the generator is ac coupled to the input of the CRT
driver. V
LM2413.
Application Hints
INTRODUCTION
National Semiconductor (NSC) is committed to providing ap-
plication information that assists our customers in obtaining
the best performance possible from our products. The follow-
ing information is provided in order to support this commit-
ment. 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
b
ADJ
limits the current through the base of Q2. Q1 and
input sets the DC operating range of the
CC
LOAD
rail, minimizing the power dissipation
to emulate the actual application
at the output form a 200:1
4
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 pur-
poses. When working with high bandwidth circuits, good lay-
out practices are also critical to achieving maximum perfor-
mance.
POWER SUPPY BYPASS
Since the LM2413 is a very high bandwidth amplifier, proper
power supply bypassing is critical for optimum performance.
Improper power supply bypassing can result in large over-
shoot, ringing and oscillation. A 0.1 µF capacitor should be
connected from the supply pin, V
the supply and ground pins as is practical. Additionally, a 10
µF to 100 µF electrolytic capacitor should be connected from
the supply pin to ground. The electrolytic capacitor should
also be placed reasonably close to the LM2413’s supply and
ground pins. A 0.1 µF capacitor should be connected from
the bias pin, V
part.
ARC PROTECTION
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 volt-
age, but to a value that is much higher than allowable on the
LM2413. This fast, high voltage, high-energy pulse can dam-
age the LM2413 output stage. The application circuit shown
in Figure 9 is designed to help clamp the voltage at the out-
put of the LM2413 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. D1 and D2 should
have short, low impedance connections to V
respectively. The cathode of D1 should be located very close
to a separately decoupled bypass capacitor. The ground
connection of the diode and the decoupling capacitor should
be very close to the LM2413 ground. This will significantly re-
duce the high frequency voltage transients that the LM2413
would be subjected to during an arc-over condition. Resistor
R2 limits the arc-over current that is seen by the diodes while
R1 limits the current into the LM2413 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. Inductor L1 is critical to reduce the inital
high frequency voltage levels that the LM2413 would be sub-
jected to during an arc-over. Having large value resistors for
R1 and R2 would be desirable, but this has the effect of in-
creasing rise and fall times. The inductor will not only help
protect the device but it will also help optimize 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 values of L1 and R1 may need to be
adjusted for a particular application. The recommended mini-
mum value for R1 is 110 , with L1 = .12 µH.
BB
, to ground, as close as is practical to the
CC
, to ground, as close to
CC
and ground

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