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ADM8830 Datasheet(PDF) 7 Page - Analog Devices |
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ADM8830 Datasheet(HTML) 7 Page - Analog Devices |
7 / 8 page –6– ADM8830 ADM8830 –7– SCANNING AND BLANKING A TFT LCD panel is essentially made up of a bank of capacitors, each representing a pixel in the display.These capacitors store different levels of charge, depending on the amount of lumines- cence required for a given pixel.When a picture is being displayed on the panel, a scan of all the pixel capacitors is performed, placing different levels of charge on each in order to create the image.The process of updating the display like this is called “scanning.” Once scanned, an image will be held by pixel capacitance and the con- troller and source line drivers can be put into a low power mode. This low power mode is referred to as the blanking mode on the ADM8830. Over a finite period of time, this pixel charge will leak and the capacitors will have to be refreshed in order to maintain the image. The ADM8830 caters to the two modes of operation described above as follows.When the TFT LCD panel is in scanning mode, a logic high on the SCAN/BLANK input places the device in high current power mode, providing extra power (extra current) to the LCD controller and the source line drivers. If the panel continues to be updated (as when a moving picture is being displayed), then the ADM8830 can be continually operated in scanning mode. If the same image is kept on the panel, a logic low is applied to the SCAN/BLANK input and the ADM8830 enters blanking (low current) mode. Depending on how often the image is being updated, the ADM8830 can be operated with a variable SCAN/BLANK duty cycle.This helps to maximize power efficiency and therefore extends the battery life. 90% 10% tR tF tH tT tR: RISETIME tF: FALLTIME tH tT @ 100% = DUTY CYCLE Figure 1. Duty Cycle of External Clock POWER SEQUENCING The gate drive supplies must be sequenced such that the –10 V supply is up before the +15 V supply for the TFT panel to power up correctly.The ADM8830 controls this sequence.When the device is turned on (a logic high on SHDN), the ADM8830 allows the –10 V output to ramp immediately but holds off the +15 V output. It continues to do this until the negative output has reached –3 V. At this point, the positive output is enabled and allowed to ramp up to +15 V.This sequence is highlighted in Figure 2. VCC LOAD SCAN/BLANK EXTERNAL CLOCK SHDN +5V +15V –10V tF5V tF15V tR10V tR15V tR5V tDELAY tF10V –3V 90% 10% 10% 90% Figure 2. Power Sequence TRANSIENT RESPONSE The ADM8830 features extremely fast transient response, making it very suitable for fast image updates on TFT LCD panels.This means that even under changing load conditions there is still very effective regulation of the 5 V output.TPCs 10 and 11 show how the 5.1 V output responds when a maximum load is dynamically connected and disconnected. Note that the output settles within 5 µs to less than 1% of the output level. EXTERNAL CLOCK The ADM8830 has an internal 100 kHz oscillator, but an external clock source can also be used to clock the part.This clock source must be applied to the CLKIN pin. Power is saved during blank- ing periods by disabling the internal oscillator and switching to the lower frequency external clock source.To achieve optimum performance of the charge pump circuitry, it is important that the duty cycle of the external clock source be 50% and that the rise and fall times be less than 20 ns. SOLDER MASK BOARD METALLIZATION DIMENSIONS IN MILLIMETERS 0.2 0.25 0.5 0.75 0.28 0.4 0.25 0.9 3.10 1.95 2.10 Figure 3. Suggested LFCSP 4 mm 4 mm 20-Lead Land Pattern REV. B REV. B |
Similar Part No. - ADM8830_15 |
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Similar Description - ADM8830_15 |
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