Motore di ricerca datesheet componenti elettronici |
|
LM2403 Scheda tecnica(PDF) 5 Page - National Semiconductor (TI) |
|
|
LM2403 Scheda tecnica(HTML) 5 Page - National Semiconductor (TI) |
5 / 11 page Application Hints (Continued) will also help optimize rise and fall times as well as minimize EMI. For proper arc protection, it is important to not omit any of the arc protection components shown in Figure 10. OPTIMIZING TRANSIENT RESPONSE Referring to Figure 10, there are three components (R1, R2 and L1) that can be adjusted to optimize the transient re- sponse of the application circuit. Increasing the values of R1 and R2 will slow the circuit down while decreasing over- shoot. Increasing the value of L1 will speed up the circuit as well as increase overshoot. It is very important to use induc- tors with very high self-resonant frequencies, preferably above 300 MHz. Ferrite core inductors from J.W. Miller Mag- netics (part # 78FR12M) were used for optimizing the perfor- mance of the device in the NSC application board. The val- ues shown in Figure 10 can be used as a good starting point for the evaluation of the LM2403. The NSC demo board also has a position open to add a resistor in parallel with L1. This resistor can be used to help control overshoot. Using vari- able resistors for R1 and the parallel resistor is a great way to help dial in the values needed for optimum performance in a given application. Pull-up Resistors Optimizing the performance of the LM2403 does require the use of pull-up resistors at the outputs of the CRT driver. These resistors are shown as R100, R101, and R102 in the schematic. If you have a demo board form National please note that these resistors have been added on the back of the board since there is no PCB location for the pull-up resistors. Because of the improved performance with these resistors, all demo boards have been shipped with the added pull-up resistors. The LM2403 does have some crossover distortion, normal for any AB amplifier such as the LM2403. Adding the pull-up resistors does add more bias to Q3 ( Figure 1) thus minimizing the crossover distortion. The LM2403 is normally used in high end monitors, so it is highly recommended that the 12k pull-up resistors be used in any design using the LM2403. Selecting a 12k resistor provides the needed pull-up current and limits the worst case power dissipation to 1/4W (white level at 25V). In some applications pull-down resistors may be preferred. Using 12k resistors gives acceptable performance, but this will require the use of 1/2W resistors. Normally the power save mode establishes whether pull-up or pull-down resis- tors are preferred. If the setup of the power save mode in the monitor gives a low output at the LM2403, then the pull-down resistors would be preferred, if the 80V supply is still turned on. Effect of Load Capacitance The output rise and fall times as well as overshoot will vary as the load capacitance varies. The values of the output cir- cuit (R1, R2 and L1 in Figure 10) should be chosen based on the nominal load capacitance. Once this is done the perfor- mance of the design can be checked by varying the load based on what the expected variation will be. For example, suppose you needed to drive a 10 pF (±20%) load with a 40V p-p waveform. First, you would pick the values of R1, R2 and L1 that give the desired response with a 10 pF load. Then you would test the design when driving an 8 pF load and a 12 pF load. The table below summarizes the re- sults from doing this exercise in a test board in the NSC lab. The output signal swing was 40V p-p from 65V to 25V. Parameter 8 pF 10 pF 12 pF Rise Time 4.1 4.2 4.3 Overshoot 1% 5% 10% Fall Time 4.4 4.6 4.7 Overshoot 1% 2% 5% The example above clearly demonstrates the importance of having a good estimate of the range of 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 30 V DC to 50 VDC. The rise time shows about twice as much variation as the fall time, however the maximum variation relative to the center data point (40 V DC) is less than 10%. Operation with V CC = 70V The closed loop topography of the LM2403 allows operation down to 10V above ground. If the user can limit the white level between 10V and 20V, then operation with V CC = 70V is possible. Operating the LM2403 with V CC = 70V will re- quire the same current even though the supply voltage has dropped by 12.5%. This results in a power savings of 12.5% (as high a 1.5W), allowing a reduction in the size of the heat- sink. Figure 8 shows the output waveform of the LM2403 op- erating at a white level of 15V, and a peak-to-peak output swing of 40V. Below is a summary of the LM2403 rise and fall times with various output offset levels with V CC = 70V. DS100082-10 FIGURE 10. One Channel of the LM2403 with the Recommended Arc Protection Circuit www.national.com 5 |
Codice articolo simile - LM2403 |
|
Descrizione simile - LM2403 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEETIT.COM |
Lei ha avuto il aiuto da alldatasheet? [ DONATE ] |
Di alldatasheet | Richest di pubblicita | contatti | Privacy Policy | scambio Link | Ricerca produttore 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 |