Datasheet LM2479NA Datasheet (NSC)

LM2479
120V Triple Bias Clamp

LM2479 120V Triple Bias Clamp

October 2000

General Description

The LM2479 is an Integrated 120V triple bias clamp circuit
for DC recovery of each of the AC coupled outputs of a CRT
driver. It is well matched with the DAC outputs of the
LM126X family of pre-amplifiers. Each amplifier has its gain
internally set to -18. The IC is packaged in an industry
standard 8 lead molded DIP package.

n High input impedance
n Single supply operation
n Matched to the LM126X family of preamplifiers

Recommended Applications

n CRT monitors requiring DC restoration at the cathodes

Features

n Wide range integrated triple bias clamp

Block Diagrams Package Pinout

FIGURE 2. LM2479 Package Pinout

Order Number LM2479NA

NS Package Number: N08E

DS101391-2

DS101391-1

FIGURE 1. Simplified Schematic (One Channel)

© 2000 National Semiconductor Corporation DS101391 www.national.com

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

LM2479

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

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

CC

IN

STG

-65˚C to +150˚C

+130V

0V to 5V

ESD Tolerance, Machine Model 200V

Limits of Operating Ranges (Note 3)

V

CC

V

OUT,VCC

= 120V 50 to 120V

Ambient Temperature Range, T

A

110 to 125

Lead Temperature (Soldering,

<

10sec.) 300˚C

DC CLAMP ELECTRICAL CHARACTERISTICS TARGETS AND LIMIT

Unless otherwise noted: VCC= +120V, VIN= 2.25VDC,TA= 25˚C.

Symbol Spec Parameter Conditions Min Typ Max Units

I

CC

V

OUT

V

OUT-Range

A

V

LE Linearity Error See Note 1 5 %
R

IN

Note 1: Linearity Error is the variation in DC gain from VIN= 1.0V to VIN= 4.0V.
Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur.
Note 3: 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 4: All voltages are measured with respect to GND, unless otherwise specified.

Supply Current All channels 2.3 3.5 mA
DC Output Voltage 83 87 91 V
Output Voltage Range VINRange = 1.0V - 4.0V 53 V
DC Voltage Gain -16 -18 -20

Input Resistance 24K Ω

0 to 70˚C

DC

Test Circuit

Figure 3

measurements at the output.

shows the test circuit for evaluation of the LM2479 Clamp Amplifier. A high impedance VM (>100MΩ) is used for DC

DS101391-3

FIGURE 3. Test Circuit (One Channel)

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Typical Performance Characteristics

(VCC= +120V), Test Circuit - Figure 3 unless otherwise specified.

DS101391-4

FIGURE 4. V

out

vs V

in

THEORY OF OPERATION

The circuit diagram of the LM2479 is shown in Figure 1. The
DC clamp circuit amplifies the input signal by -18 and the
gain is set by the resistor ratio of 18R and R. The output
requires pull-up resistor to 120V. Figure 2 shows the test
circuit used for evaluation of the LM2479 Clamp Amplifier. A
high impedance voltmeter (100MΩ) is used for DC measure­ments at the output. The DC transfer function is shown in
Figure 4.

the supply pin to ground. The electrolytic capacitor should
also be placed reasonably close to the LM2479’s supply and
ground pins.

Application Circuit

The application circuit shown in Figure 5 is designed to help
clamp the voltage at the output of the driver to the desired
level. Capacitor C
the clamp diode, D

stabilizes the entire node at the anode of

4

, by creating a low impedance at high

3

frequencies. Figure 5 also shows the standard application
circuit topology when used with an LM246X CRT driver. It
shows all the components necessary to optimize perfor­mance as well as to protect against damage from a CRT arc
event. No additional components are required to protect the
LM2479 from arc damage.

LM2479

APPLICATION HINTS

Power Supply Bypass

The LM2479 should have proper power supply bypassing for
optimum performance. A 0.1µF capacitor should be con­nected from the supply pin, V
supply and ground pins as is practical. Additionally, a 1.0µF
electrolycelectrolytictic capacitor should be connected from

, to ground, as close to the

cc

DS101391-7

FIGURE 5. One Channel of the LM2479 and LM246X

Application Circuit

Demonstration Hardware

National Semiconductor has designed a demonstration
neckboard for the LM126X, LM246X, and the LM2479
chipset. Toobtain demonstration boards contact the National
Semiconductor Sales Office in your region.

www.national.com3

Physical Dimensions inches (millimeters) unless otherwise noted

LM2479 120V Triple Bias Clamp

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

Molded Dual-In-Line Package (N)

NS Package Number N08E

Order NumbernLM2479NA

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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the

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.

labeling, can be reasonably expected to result in a
significant injury to the user.

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Corporation

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National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

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