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LM1247 データシート(PDF) 8 Page - National Semiconductor (TI) |
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LM1247 データシート(HTML) 8 Page - National Semiconductor (TI) |
8 / 48 page Typical Performance Characteristics V CC = 5V, TA = 25˚C unless otherwise specified (Continued) SYSTEM INTERFACE SIGNALS The Horizontal and Vertical Blanking and the Clamping input signals are important for proper functionality of the LM1247. Both blanking inputs must be present for OSD synchronization. In addition, the Horizontal blanking input also assists in setting the proper cathode black level, along with the Clamping pulse. The Vertical blanking input initiates a blanking level at the LM1247 outputs which is programmable from 3 to 127 lines (we recommend at least 10). Both horizontal and vertical blanking can be individually disabled, if desired. Figure 2 and Figure 3 show the case where the Horizontal and Vertical inputs are logic levels. Figure 2 shows the smaller pin 24 voltage superimposed on the horizontal blanking pulse input to the neck board with R H = 4.7k and C17 = 0.1 µF. Note where the voltage at pin 24 is clamped to about 1 volt when the pin is sinking current. Figure 3 shows the smaller pin 1 voltage superimposed on the vertical blanking input to the neck board with C 4 jumpered and RV = 4.7k. These component values correspond to the application circuit of Figure 9. Figure 4 and Figure 5 show the case where the horizontal and vertical inputs are from deflection. Figure 4 shows the pin 24 voltage which is derived from a horizontal flyback pulse of 35V peak to peak with R H = 8.2K and C17 jumpered. Figure 5 shows the pin 1 voltage which is derived from a vertical flyback pulse of 55V peak to peak with C 4 = 1500 pF and RV = 120k. Figure 6 shows the pin 23 clamp input voltage superimposed on the neck board clamp logic input pulse. R 31 = 1k and should be chosen to limit the pin 23 voltage to about 2.5V peak to peak. This corresponds to the application circuit given in Figure 9. CATHODE RESPONSE Figure 7 shows the response at the red cathode for the application circuit in Figures 9, 10. The input video risetime is 1.5 ns. The resulting leading edge has a 7.1 ns risetime and a 7.6% overshoot, while the trailing edge has a 7.1 ns risetime and a 6.9% overshoot with an LM2467 driver. ABL GAIN REDUCTION The ABL function reduces the contrast level of the LM1247 as the voltage on pin 22 is lowered from V CC to around 2V. Figure 8 shows the amount of gain reduction as the voltage is lowered from V CC (5.0V) to 2V. The gain reduction is small until V22 reaches the knee anound 3.7V, where the slope increases. Many system designs will require about 3 dB to 5 dB of gain reduction in full beam limiting. Additional attenuation is possible, and can be used in special circumstances. However, in this case, video performance such as video linearity and tracking between channels will tend to depart from normal specifications. OSD PHASE LOCKED LOOP Table 3 shows the recommended horizontal scan rate ranges (in kHz) for each combination of PLL register setting, 0x843E [1:0], and the pixels per line register setting, 0x8401 [7:5]. These ranges are recommended for chip ambient temperatures of 25oCto 70oC. While the OSD PLL will lock for other register combinations and at scan rates outside these ranges, the performance of the loop will be improved if these recommendations are followed. NR means the combination of PLL and PPL is not recommended for any scan rate. 20048408 FIGURE 8. ABL Gain Reduction Curve www.national.com 8 |
同様の部品番号 - LM1247 |
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同様の説明 - LM1247 |
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