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MIC2844AYMT Datasheet(PDF) 8 Page - Micrel Semiconductor |
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MIC2844AYMT Datasheet(HTML) 8 Page - Micrel Semiconductor |
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8 / 14 page  Micrel Inc. MIC2844A August 2009 8 M9999-080309-D Application Information Brightness Level (0 - 48) Average Duty Cycle (%) Average ILED (mA) IPEAK (mA) 0 100 12 1 80 9.6 2 60 7.2 3 48.33 5.8 4 36.67 4.4 5 29.17 3.5 6 21.67 2.6 7 16.67 2 8 11.67 1.4 9 9.17 1.1 10 6.67 0.8 11 5 0.6 12 3.33 0.4 13 2.5 0.3 14 1.67 0.2 15 0.83 0.1 60% of IPEAK RSET = 20.5kΩ IPEAK = 12mA 16 0 0 0 17 0.83 0.1 60% of IPEAK 18 0.83 0.17 19 1.25 0.25 20 1.67 0.33 21 2.08 0.42 22 2.5 0.5 23 2.92 0.58 24 3.33 0.67 25 4.17 0.83 26 5 1 27 5.83 1.17 28 6.67 1.33 29 7.92 1.58 30 9.17 1.83 31 10.42 2.08 32 11.67 2.33 33 14.17 2.83 34 16.67 3.33 35 19.17 3.83 36 21.67 4.33 37 25.42 5.08 38 29.17 5.83 39 32.92 6.58 40 36.67 7.33 41 42.5 8.5 42 48.33 9.67 43 54.17 10.83 44 60 12 45 70 14 46 80 16 47 90 18 48 100 20 100% of IPEAK RSET = 20.5kΩ IPEAK = 20mA Table 1. Digital Interface Brightness Level Table Dynamic Average Matching™ (DAM™) The Dynamic Average Matching™ architecture multiplexes four voltage references to provide highly accurate LED current and channel matching. The MIC2844A achieves industry leading LED channel matching of 1.5% across the entire dimming range. High Current Parallel Operation RSET VIN C1 Low Dropout Linear Driver Digital Control VIN U1 MIC2844AYMT DC Figure 3. High Current LED Driver Circuit The linear drivers are independent of each other and can be used individually or paralleled in any combination for higher current applications. A single WLED can be driven with all 6 linear drivers by connecting D1 through D6 in parallel to the cathode of the WLED as shown in Figure 3. This will generate a current 6 times the individual channel current and can be used for higher current WLEDs such as those used in flash or torch applications. Digital Dimming The MIC2844A utilizes an internal dynamic pulse width to generate an average duty cycle for each brightness level. By varying the duty cycle the average current achieves 49 logarithmically spaced brightness levels. This generates a brightness scale similar to the perception of brightness seen by the “human eye.” Figure 4 shows the LED current for a single channel at different brightness levels. When dimming, the D1 through D6 pins are 60° out of phase from each other to reduce electromagnetic interference. The MIC2844A uses an internal frequency of approximately 700Hz to dim the WLEDs. With the period of approximately 1.43ms, the 60° phase shift equates to a timing offset of 238μs. As shown in Figure 5, brightness level 32 was selected to show the phase shift across the channels. |
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