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LM2480 80V Triple Bias Clamp
December 2000
LM2480 80V Triple Bias Clamp
General Description
The LM2480 driver is an Integrated 80V 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
DS200083-2
FIGURE 2. LM2480 Package Pinout Order Number LM2480NA NS Package Number: N08E
DS200083-1
FIGURE 1. Simplified Schematic (One Channel)
(c) 2000 National Semiconductor Corporation
DS200083
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LM2480
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage, VCC Input Voltage, VIN Storage Temperature Range, TSTG Lead Temperature (Soldering, < 10sec.) +90V 0V to 5V -65C to +150C 300C
ESD Tolerance, Machine Model
200V (Note 3) 70V to 85V 10V to VCC 0 to 70C
Limits of Operating Ranges
VCC VOUT Ambient Temperature Range, TA
DC CLAMP ELECTRICAL CHARACTERISTICS TARGETS AND LIMIT
Unless otherwise noted: VCC = +80V, VIN = 2.25VDC, TA = 25C. Symbol ICC VOUT VOUT-Range AV LE RIN Spec Parameter Supply Current DC Output Voltage Output Voltage Range DC Voltage Gain Linearity Error Input Resistance See Note 1 VIN Range = 1.0V - 4.0V -16 Conditions All channels 42 Min Typ 2.1 46 53 -18 5 34K -20 % Max 3.5 50 Units mA VDC V
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.
Test Circuit
DS200083-3
FIGURE 3. Test Circuit (One Channel)
Figure 3 shows the test circuit for evaluation of the LM2480 Clamp Amplifier. A high impedance VM ( > 100M) is used for DC measurements at the output.
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LM2480
Typical Performance Characteristics
(VCC = +80V), Test Circuit - Figure 3 unless otherwise specified. the supply pin to ground. The electrolytic capacitor should also be placed reasonably close to the LM2480'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 C4 stabilizes the entire node at the anode of the clamp diode, D3, by creating a low impedance at high 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 LM2480 from arc damage.
DS200083-4
FIGURE 4. Vout vs Vin
THEORY OF OPERATION
The circuit diagram of the LM2480 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 80V. Figure 2 shows the test circuit used for evaluation of the LM2480 Clamp Amplifier. A high impedance voltmeter (100M) is used for DC measurements at the output. The DC transfer function is shown in Figure 4.
APPLICATION HINTS
Power Supply Bypass The LM2480 should have proper power supply bypassing for optimum performance. A 0.1F capacitor should be connected from the supply pin, Vcc, to ground, as close to the supply and ground pins as is practical. Additionally, a 1.0F electrolycelectrolytictic capacitor should be connected from
DS200083-7
FIGURE 5. One Channel of the LM2480 and LM246X Application Circuit Demonstration Hardware National Semiconductor has designed a demonstration neckboard for the LM126X, LM246X, and the LM2480 chipset. To obtain demonstration boards contact the National Semiconductor Sales Office in your region.
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LM2480 80V Triple Bias Clamp
Physical Dimensions
inches (millimeters) unless otherwise noted
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
LIFE SUPPORT POLICY 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 labeling, can be reasonably expected to result in a significant injury to the user.
National Semiconductor Corporation Americas Tel: 1-800-272-9959 Fax: 1-800-737-7018 Email: support@nsc.com www.national.com National Semiconductor Europe Fax: +49 (0) 180-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Francais Tel: +33 (0) 1 41 91 8790
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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National Semiconductor Japan Ltd. Tel: 81-3-5639-7560 Fax: 81-3-5639-7507
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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