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FAN5702UMP20X Datasheet(PDF) 11 Page - Fairchild Semiconductor |
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FAN5702UMP20X Datasheet(HTML) 11 Page - Fairchild Semiconductor |
11 / 17 page © 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com FAN5702 • Rev. 1.0.3 11 Circuit Description The FAN5702 is a white LED driver system based on an adaptive 1.5x charge pump capable of supplying up to 180mA of total output current. The tightly matched current sinks ensure uniform brightness between the LEDs. Each LED has a common anode configuration with its peak drive current set during manufacturing (see Ordering Information and ISET). An I 2C-compatible interface is used to vary the brightness within the individual current sinks as well as configure the grouping. Each LED is controlled with 64 exponentially spaced analog brightness control levels through I 2C, as indicated in Table 1. For maximum flexibility, the FAN5702 can be programmed with five independently controlled LED banks; by default, arranged as 2,1,1,1,1 (first two LEDs represent Group A). Through I 2C, the device can be reconfigured to add up to six LEDs to Group A as needed by application requirements. Charge Pump The charge pump operates in either 1x mode, where VOUT is connected to VIN through a bypass switch, or in 1.5x mode. The circuit operates in 1x mode until the LED with the highest forward voltage (VLED(MAX)) can no longer maintain current regulation. At that point, 1.5x mode begins. If the lowest active cathode voltage is greater than 1.8V, the charge pump switches back to 1x mode. IC Enable By default the General Purpose register bit 7 = 0, the EN pin functions as enable/disable. When the EN pin is LOW, all circuit functions, including I 2C, are disabled and the registers are set to their default values. When the EN pin HIGH, I 2C interface is enabled. The LEDs can be turned on/off by writing to the General Purpose register. The user can always communicate via I 2C with the device to change register settings regardless of whether any LED is on or off. PWM Dimming By programming the General Purpose register bit 7 = 1, the EN pin is reappropriated to a PWM dimming input. Applying a PWM signal to this pin controls the LED current waveform to be ON when the PWM dimming pin is HIGH and OFF when the PWM dimming pin is LOW. By using this pin in conjunction with the I 2C register dimming, the part can achieve higher dimming resolution. For instance, an 8-bit PWM dimming signal applied along with the 6-bit register dimming yields better than 14 bits of resolution To change the PWM dimming pin back to the EN function, set the General Purpose register bit 7 to 0. Register Controlled Brightness The DC value of the LED current is modulated according to the values in Table 1. Current is expressed as a percentage of the full scale current and is illustrated with a 20mA ISET. Table 1. Brightness Control Dimming Code (Bx5-Bx0) Current Level ILED (mA) (ISET=20mA) 000000 0.125% 0.025 000001 0.188% 0.038 000010 0.249% 0.050 000011 0.312% 0.063 000100 0.374% 0.075 000101 0.438% 0.088 000110 0.499% 0.100 000111 0.560% 0.113 001000 0.622% 0.125 001001 0.692% 0.138 001010 0.750% 0.150 001011 0.810% 0.163 001100 0.875% 0.175 001101 0.938% 0.188 001110 1.004% 0.200 001111 1.124% 0.225 010000 1.250% 0.250 010001 1.375% 0.275 010010 1.499% 0.300 010011 1.625% 0.325 010100 1.750% 0.350 010101 1.881% 0.375 010110 2.063% 0.413 010111 2.249% 0.450 011000 2.438% 0.488 011001 2.687% 0.538 011010 2.939% 0.588 011011 3.186% 0.638 011100 3.562% 0.713 011101 3.936% 0.788 011110 4.310% 0.863 011111 4.813% 0.963 100000 5.314% 1.063 100001 5.936% 1.188 100010 6.565% 1.313 100011 7.313% 1.463 100100 8.059% 1.613 100101 8.938% 1.788 100110 9.876% 1.975 100111 10.874% 2.175 101000 12.005% 2.400 101001 13.253% 2.650 101010 14.618% 2.925 101011 16.124% 3.225 101100 17.881% 3.575 101101 19.875% 3.975 101110 22.121% 4.425 101111 24.621% 4.925 110000 27.376% 5.475 110001 30.373% 6.075 110010 33.623% 6.725 110011 37.124% 7.425 110100 40.873% 8.175 110101 44.875% 8.975 110110 49.124% 9.825 110111 53.624% 10.725 111000 58.375% 11.675 111001 63.378% 12.675 111010 68.625% 13.725 111011 74.122% 14.825 111100 79.874% 15.975 111101 85.873% 17.175 111110 92.373% 18.475 111111 100.000% 20.000 |
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