LM2481 145V Triple Bias Clamp General Description n Matched to LM2421 HDTV Driver The LM2481 driver is an Integrated 145V triple bias clamp circuit for DC recovery of each of the AC coupled outputs of a HDTV 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 -20. The LM2481 is packaged in an industry standard 14 lead molded plastic dual-in-line package. Applications n AC coupled HDTV applications using the 1080i and 720p formats Features n Wide range integrated triple bias clamp n High input impedance Schematic and Connection Diagrams 20039832 FIGURE 1. Simplified Schematic Diagram (One Channel) 20039833 Top View Order Number LM2481NA © 2002 National Semiconductor Corporation DS200398 www.national.com LM2481 145V Triple Bias Clamp June 2002 LM2481 Absolute Maximum Ratings Machine Model (Notes 1, 200V Human Body Model 3) Bias Voltage, VBB +15V Input Voltage, VIN -0.5V to VBB +0.55V Storage Temperature Range, TSTG 70˚C Limits of Operating Ranges -65˚C to +150˚C Lead Temperature (Soldering, < 10sec.) 150˚C θJA (Typ) (Note 5) +155V Supply Voltage, VCC 2KV Max Junction Temperature If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VCC 130V to 150V VBB 7V to 13V VIN 1V to 5V VOUT 25V to 140V Ambient Temperature Range, TA 300˚C (Note 3) 0˚C to 70˚C ESD Tolerance DC Clamp Electrical Characteristics (See Figure 2 for Test Circuit) Unless otherwise noted: VCC = +145V, VBB = 8V, VIN = +2.5V, TA = 30˚C Symbol Parameter Conditions ICC Supply Current All three channels, includes 100K pull-up resistor current IBB Bias Supply Current All channels VOUT DC Output Voltage VOUT-Range Output Voltage Range AV DC Voltage Gain LE Linearity Error Min Typ Max Units 4.5 7 mA 2 100 108 VIN Range = +1.5V to 4.5V mA 115 VDC -22 V/V 60 -18 -20 See Note 4 5 V % Note 1: Absolute Maximum Ratings indicate 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 the 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 conditions. 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= 1.5 volts to VIN = 4.5 volts. Note 5: Measured with 1in2 copper on PCB connected to pins 3, 4, 5, 10, 11, 12. See Thermal Considerations Section. Test Circuit 20039834 FIGURE 2. Test Circuit Figure 2 shows the test circuit for evaluation of the LM2481 Clamp Amplifier. A high impedance Voltmeter ( > 100MΩ) is used for DC measurements at the output. www.national.com 2 LM2481 Typical Performance Characteristics (VCC = +145V, VBB = +8V, VIN = +2.5V, Test Circuit - Figure 2) • The traces connecting the LM126X preamp DACs and the LM2481 input pins (pins 1, 13, and 14) should be run around the top of the LM2421. They should not go through the output circuit of the LM2421. • C43, C44, and C45 should be located close to the LM126X preamp. • R44, R45, and R46 should be located close to the LM2481. • C21, C24, and C25 on the output pins of the LM2481 (pins 6, 8, and 9) should be located close to the LM2481. The grounds of these capacitors should have a short direct return to GND (pins 3, 4, 5, 10, 11, and 12) of the LM2481. • C9 and C36 on the supply lines (pins 2 and 7) should be located close to the LM2481. The grounds of these capacitors should have a short direct return to GND (pins 3, 4, 5, 10, 11, and 12) of the LM2481. • The ground of the LM2481 should have a short direct connection to the ground of the LM2421. 20039835 FIGURE 3. Vout vs Vin Theory of Operation Thermal Considerations The simplified circuit diagram of the LM2481 is shown in Figure 1. The DC clamp circuit amplifies the input signal by -20 and the gain is set by the resistor ratio of 20R and R. The output will require a pull-up resistor to 145V. The package the LM2481 is in uses the ground pins (3, 4, 5, 10, 11, and 12) to conduct heat from the LM2481. These pins should be connected to a ground plane that acts as a heat sink. See the example ground plane connected to these pins in the National Semiconductor PCB shown in Figure 7. Figure 4 is used to determine the size of ground plane heat sink. The lines in Figure 4 represent a junction temperature of 150˚C when the size of heat sink noted by the line is used. The area under the line is the safe operating area. Using Figure 4, the following example shows how to determine the size of the ground plane. The LM2481 uses about 0.4W of quiescent power. If VCC = +145V, and each channel of the LM2481 needs to sink an average of 1mA, the LM2481 will use: 0.4W + 3 x (145V x 1mA ) = 0.835W Figure 4 shows that the LM2481 dissipating 0.835W with one sq. in. of copper ground plane heat sink is in the safe operating range for any ambient temperature up to 70˚C. Figure 2 shows the test circuit for evaluation of the LM2481 Clamp Amplifier. A high impedance voltmeter ( > 100MΩ) is used for DC measurements at the output. Application Hints INTRODUCTION 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 performance in a given application. The values shown in this document can be used as a starting point for evaluation purposes. POWER SUPPLY BYPASS The LM2481 should have proper power supply bypassing for optimum performance. A 0.1 µF capacitor should be connected from the supply pins, VCC and VBB, to ground, as close to the supply and ground pins as is practical. Additionally, a 1 µF electrolytic capacitor should be connected from the supply pins to ground. The electrolytic capacitor should also be placed reasonably close to the LM2481’s supply and ground pins. 20039836 ARC PROTECTION During normal CRT operation, internal arcing may occasionally occur. To protect the LM2481 against arcing the following steps should be done (See Figure 7): FIGURE 4. Maximum Power Dissipation vs. Ambient Temperature 3 www.national.com LM2481 Typical Application NSC Demonstration Board A typical application of the LM2481 is shown in Figures 5 and Figure 6. Used in conjunction with an LM126X Preamp and an LM2421 CRT Driver, a complete video channel from input to CRT cathode can be achieved. Performance is ideal for HDTV applications. Figure 5 and Figure 6 are the schematic for the NSC demonstration board that can be used to evaluate the LM126X/LM2421/LM2481. Figure 7 shows the routing and component placement on the NSC LM126X/LM2421/LM2481 demonstration board. The schematic of the board is shown in Figure 5 and Figure 6. This board provides a good example of a layout that can be used as a guide. www.national.com 4 LM2481 Demonstration Board Schematics 20039829 FIGURE 5. LM126X/LM2421/LM2481 Demonstration Board Schematic 5 www.national.com LM2481 Demonstration Board Schematics (Continued) 20039830 FIGURE 6. LM126X/LM2421/LM2481 Demonstration Board Schematic www.national.com 6 LM2481 Demonstration Board Schematics (Continued) 20039831 FIGURE 7. LM126X/LM2421/LM2481 Demonstration Board Layout 7 www.national.com LM2481 145V 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 Order Number LM2481NA NS Package Number N14A 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 Email: [email protected] www.national.com National Semiconductor Europe Fax: +49 (0) 180-530 85 86 Email: [email protected] Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français 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. National Semiconductor Asia Pacific Customer Response Group Tel: 65-2544466 Fax: 65-2504466 Email: [email protected] 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.