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LM2466 Arkusz danych(PDF) 6 Page - Texas Instruments |
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LM2466 Arkusz danych(HTML) 6 Page - Texas Instruments |
6 / 14 page OBSOLETE LM2466 SNOSA14B – SEPTEMBER 2003 – REVISED APRIL 2013 www.ti.com THEORY OF OPERATION The LM2466 is a high voltage monolithic three channel CRT driver suitable for high resolution display applications. The LM2466 operates with 80V and 12V power supplies. The part is housed in the industry standard 9-lead TO-220 molded plastic power package. The circuit diagram of the LM2466 is shown in Figure 1. 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 −20. 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. Figure 2 shows a typical test circuit for evaluation of the LM2466. This circuit is designed to allow testing of the LM2466 in a 50 Ω environment without the use of an expensive FET probe. In this test circuit, the two 2.49kΩ resistors form a 200:1 wideband, low capacitance probe when connected to a 50 Ω coaxial cable and a 50Ω load (such as a 50 Ω oscilloscope input). The input signal from the generator is ac coupled to the base of Q5. APPLICATION HINTS Introduction Texas Instruments (TI) 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 TI. 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. When working with high bandwidth circuits, good layout practices are also critical to achieving maximum performance. Important Information The LM2466 performance is targeted for the VGA (640 x 480) to XGA (1024 x 768, 85 Hz refresh) resolution market. The application circuits shown in this document to optimize performance and to protect against damage from CRT arcover are designed specifically for the LM2466. If another member of the LM246X family is used, please refer to its datasheet. Power Supply Bypass Since the LM2466 is a wide bandwidth amplifier, proper power supply bypassing is critical for optimum performance. Improper power supply bypassing can result in large overshoot, ringing or oscillation. 0.1 µF capacitors should be connected from the supply pins, VCC and VBB, to ground, as close to the LM2466 as is practical. Additionally, a 47 µF or larger electrolytic capacitor should be connected from both supply pins to ground reasonably close to the LM2466. Arc Protection During normal CRT operation, internal arcing may occasionally occur. Spark gaps, in the range of 200V, connected from the CRT cathodes to CRT ground will limit the maximum voltage, but to a value that is much higher than allowable on the LM2466. This fast, high voltage, high energy pulse can damage the LM2466 output stage. The application circuit shown in Figure 9 is designed to help clamp the voltage at the output of the LM2466 to a safe level. The clamp diodes, D1 and D2, should have a fast transient response, high peak current rating, low series impedance and low shunt capacitance. FDH400 or equivalent diodes are recommended. Do not use 1N4148 diodes for the clamp diodes. D1 and D2 should have short, low impedance connections to VCC and ground respectively. The cathode of D1 should be located very close to a separately decoupled bypass capacitor (C3 in Figure 9). The ground connection of D2 and the decoupling capacitor should be very close to the LM2466 ground. This will significantly reduce the high frequency voltage transients that the LM2466 would be subjected to during an arcover condition. Resistor R2 limits the arcover current that is seen by the diodes while R1 limits the current into the LM2466 as well as the voltage stress at the outputs of the device. R2 should be a 6 Submit Documentation Feedback Copyright © 2003–2013, Texas Instruments Incorporated Product Folder Links: LM2466 |
Podobny numer części - LM2466 |
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Podobny opis - LM2466 |
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