Datenblatt-Suchmaschine für elektronische Bauteile |
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ADD8709 Datenblatt(PDF) 10 Page - Analog Devices |
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ADD8709 Datenblatt(HTML) 10 Page - Analog Devices |
10 / 16 page ADD8709 Rev. A | Page 10 of 16 APPLICATION NOTES The ADD8709 is a gamma reference generator that allows source drivers to be optimized for the different combinations of liquid crystals, glass sizes, etc. in large LCD panels. In a typical panel application, the selected source drivers have an internal gamma curve that is not ideal for the specific panel, as shown in Figure 19. The ADD8709 allows the gamma curve in the source drivers to be adjusted appropriately, and also ensures that all of the source drivers have the same gamma curve. 16 14 12 10 PANEL GAMMA CURVE CORRECTED BY ADD8709 ORIGINAL GAMMA CURVE IN SOURCE DRIVERS 8 6 4 2 0 GAMMA REFERENCE INPUT POINTS Figure 19. Original and Corrected Gamma Curves The ADD8709 also includes a low dropout linear regulator to provide a stable reference level for the gamma curve for best panel performance. VOLTAGE REGULATOR The on-board voltage regulator provides a regulated voltage to the external resistors to set different gamma voltages. The output of the regulator is set by the two resistors, R1 and R2, and an internal reference voltage of 1.2V. In the ADD8709, R1 and R2 are external components. The output voltage can is found by VREG OUT = VREF × (R2/R1 + 1) VREF 1.2V + – R2 55k Ω R1 5k Ω VREG OUT Figure 20. Voltage Regulator MAXIMUM POWER DISSIPATION The maximum safe power dissipation in the ADD8709 package is limited by the associated rise in junction temperature (TJ) on the die. At approximately 150°C, the glass transition temper- ature, the properties of the plastic change. Even temporarily exceeding this temperature limit may change the stresses that the package exerts on the die, permanently shifting the para- metric performance of the ADD8709. Exceeding a junction temperature of 175°C for an extended period can result in changes in the silicon devices, potentially causing failure. OPERATING TEMPERATURE RANGE The junction temperature is TJ = TAMB + θJA × PDIS where: TAMB = ambient temperature. θJA = junction-to-ambient thermal resistance, in °C/watt. PDIS = power dissipated in the device, in watts. For the ADD8709, PDIS can be calculated by PDIS = VDD × IDQ + Σ(IOUT X(+) × (VDD − VOUT X)) + Σ(−IOUT X(-) × VOUTX) + (VDD – VREG OUT) × ILOAD where: VDD × IDQ = nominal system power requirements. IOUT X(+) × (VDD − VOUT X) = positive-current amplifier load power dissipation (current comes from VDD). −IOU XT(-) × VOUT X = negative-current amplifier load power dissipation (current goes to GND). (VDD – VREG OUT) × ILOAD = regulator load power dissipation. Example 1 To calculate an estimated power consumption of the ADD8709 assume: VDD × IDQ = 16 V × 15 mA = 0.240 W. (VDD – VREG OUT) × ILOAD = (16 V – 14.4 V) × 5 mA = 0.008 W. |
Ähnliche Teilenummer - ADD8709_15 |
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Ähnliche Beschreibung - ADD8709_15 |
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