Datenblatt-Suchmaschine für elektronische Bauteile |
|
LM2465 Datenblatt(PDF) 6 Page - National Semiconductor (TI) |
|
|
LM2465 Datenblatt(HTML) 6 Page - National Semiconductor (TI) |
6 / 12 page Application Hints (Continued) OPTIMIZING TRANSIENT RESPONSE Referring to Figure 9, there are three components (R1, R2 and L1) that can be adjusted to optimize the transient response of the application circuit. Increasing the values of R1 and R2 will slow the circuit down while decreasing overshoot. Increasing the value of L1 will speed up the circuit as well as increase overshoot. It is very important to use inductors with very high self-resonant frequencies, preferably above 300MHz. Ferrite core inductors from J.W. Miller Magnetics (part # 78FR--k) were used for optimizing the performance of the device in the NSC application board. The values shown in Figure 9 can be used as a good starting point for the evaluation of the LM2465. Using a variable resistor for R1 will simplify finding the value needed for optimum performance in a given application. Once the optimum value is determined, the variable resistors can be replaced with fixed values. EFFECT OF LOAD CAPACITANCE Figure 8 shows the effect of increased load capacitance on the speed of the device. This demonstrates the importance of knowing the load capacitance in the application. The rise time increased about 0.12nsec for an increase of 1pF in the load capacitance. The fall time increased about 0.10 nsec for a 1pF increase in the load capacitance. EFFECT OF OFFSET Figure 7 shows the variation in rise and fall times when the output offset of the device is varied from 40 to 50 V DC. The rise time increases less than 0.20nsec from its fastest point near 45V. The fall time becomes faster as the offset voltage increases, but the 45V offset is only 0.1nsec slower than the fastest fall time. THERMAL CONSIDERATIONS Figure 4 shows the performance of the LM2465 in the test circuit shown in Figure 2 as a function of case temperature. The figure shows that the rise time of the LM2465 increases by approximately 13% as the case temperature increases from 30˚C to 95˚C. This corresponds to a speed degradation of 2% for every 10˚C rise in case temperature. The fall time degrades around 0.3% for every 10˚C rise in case temperature. Figure 6 shows the maximum power dissipation of the LM2465 vs. Frequency when all three channels of the device are driving an 8pF load with a 40V p-p alternating one pixel on, one pixel off signal. The graph assumes a 72% active time (device operating at the specified frequency) which is typical in a monitor application. The other 28% of the time the device is assumed to be sitting at the black level (65V in this case). This graph gives the designer the information needed to determine the heat sink requirement for his application. The designer should note that if the load capacitance is increased, the AC component of the total power dissipation will also increase. The LM2465 case temperature must be maintained below 100˚C. If the maximum expected ambient temperature is 70˚C and the maximum power dissipation is 7.6W (from Figure 6, 75MHz bandwidth) then a maximum heat sink thermal resistance can be calculated: This example assumes a capacitive load of 8pF and no resistive load. TYPICAL APPLICATION A typical application of the LM2465 is shown in Figure 10 and Figure 11. Used in conjunction with an LM1267 and a LM2479/2480bias clamp, a complete video channel from monitor input to CRT cathode can be achieved. Performance is ideal for 1280 x 1024 resolution displays with pixel clock frequencies up to 135 MHz. Figure 10 and Figure 11 are the schematic for the NSC demonstration board that can be used to evaluate the LM1267/2465 /2480 combination in a monitor. PC BOARD LAYOUT CONSIDERATIONS For optimum performance, an adequate ground plane, isolation between channels, good supply bypassing and minimizing unwanted feedback are necessary. Also, the length of the signal traces from the preamplifier to the LM2465 and from the LM2465 to the CRT cathode should be as short as possible. The following references are recommended: Ott, Henry W., “Noise Reduction Techniques in Electronic Systems”, John Wiley & Sons, New York, 1976. “Video Amplifier Design for Computer Monitors”, National Semiconductor Application Note 1013. Pease, Robert A., “Troubleshooting Analog Circuits”, Butterworth-Heinemann, 1991. Because of its high small signal bandwidth, the part may oscillate in a monitor if feedback occurs around the video channel through the chassis wiring. To prevent this, leads to the video amplifier input circuit should be shielded, and input circuit wiring should be spaced as far as possible from output circuit wiring. DS200190-10 FIGURE 9. One Channel of the LM2465 with the Recommended Arc Protection Circuit www.national.com 6 |
Ähnliche Teilenummer - LM2465 |
|
Ähnliche Beschreibung - LM2465 |
|
|
Link URL |
Privatsphäre und Datenschutz |
ALLDATASHEETDE.COM |
War ALLDATASHEET hilfreich? [ DONATE ] |
Über Alldatasheet | Werbung | Kontakt | Privatsphäre und Datenschutz | Linktausch | Hersteller All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |