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ADD8708 Scheda tecnica(PDF) 10 Page - Analog Devices |
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ADD8708 Scheda tecnica(HTML) 10 Page - Analog Devices |
10 / 16 page ADD8708 Rev. 0 | Page 10 of 16 APPLICATION NOTES The ADD8708 is a mask-programmable gamma reference generator that allows source drivers to be optimized for the different combinations of liquid crystals, glass sizes, etc. in large LCD panels. It generates 18 gamma reference outputs that can be mask-programmed in 0.2% increments using the 500 matched internal resistors (see Figure 20), so that every point on the curve can be targeted within 0.1% of the desired value. TAP POINT 4 TAP POINT 3 TAP POINT 2 TAP POINT 1 TAP POINT 500 TAP POINT 499 TAP POINT 498 TAP POINT 497 EACH R = 30 Ω TYPICALLY Figure 20. 500 Mask-Programmable Resistor String In a typical panel application, the selected source drivers have an internal gamma curve that is not ideal for the specific panel (see Figure 21). The ADD8708 allows the gamma curve in the source drivers to be adjusted appropriately, and also ensures that all the source drivers have the same gamma curve. 16 14 12 10 PANEL GAMMA CURVE CORRECTED BY ADD8708 ORIGINAL GAMMA CURVE IN SOURCE DRIVERS 8 6 4 2 0 GAMMA REFERENCE INPUT POINTS Figure 21. Original and Corrected Gamma Curves The matching and tracking accuracy of the internal resistors is typically 0.1% with worst-case deviation from the desired curve within 0.4% of the ideal gamma curve, over temperature. The ADD8708 also includes a low-dropout linear regulator to provide a stable reference level for the gamma curve for optimum panel performance. TAP POINT SELECTION The ADD8708 uses a single resistor string consisting of 500 individual elements. The tap points are mask programmable and completely independent of each other. See the Tap Point and Regulator Voltage Request Form in this data sheet. VREG OUT VOUTX VINX 500–TPX TPX Figure 22. Gamma Buffers Tap Point Circuit Tap point voltages can be derived from the following equation: OUT REG X OUT V TP X V × = 500 where TPX is the desired tap point for the Xth channel. Table 5. Typical Mask Implementation1 VDD = 16 V, VREG OUT = 14.4 V, 0 ≤ X ≤ 500 Tap Point (X) Voltage Units VOUT18 500 14.400 V VOUT17 396 11.405 V VOUT16 369 10.627 V VOUT15 361 10.397 V VOUT14 354 10.195 V VOUT13 350 10.080 V VOUT12 341 9.821 V VOUT11 317 9.130 V VOUT10 299 8.611 V VOUT9 225 6.480 V VOUT8 211 6.077 V VOUT7 177 5.098 V VOUT6 167 4.810 V VOUT5 163 4.694 V VOUT4 154 4.435 V VOUT3 146 4.205 V VOUT2 118 3.398 V VOUT1 7 0.202 V _______________________________ 1ADD8708 release samples do not have these typical values. The values on the samples are nonmonotonic and can be provided upon request. |
Codice articolo simile - ADD8708_15 |
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Descrizione simile - ADD8708_15 |
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