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TLC5957 Datasheet(PDF) 14 Page - Texas Instruments |
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TLC5957 Datasheet(HTML) 14 Page - Texas Instruments |
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TLC5957 SLVSCQ4 – OCTOBER 2014 www.ti.com Device Functional Modes (continued) Table 1. CC Data vs Current Ratio and Set Current Value RATIO OF OUTPUT CC DATA (CCR or CCG or CCB) CURRENT OUTPUT CURRENT (mA, RIREF = 7.41 kΩ) TO IolcMax(%, typical) BC = 7h BC = 0h BINARY DECIMAL HEX (IolcMax =25mA) (IolcMax=3.2mA) 0 0000 0000 0 00 0 0 0 0 0000 0001 1 01 0.2 0.05 0.006 0 0000 0010 2 02 0.4 0.10 0.013 — — — — — — 1 0000 0000 256 100 50.1 12.52 1.621 (Default) (Default) (Default) — — — — — — 1 1111 1101 509 1FD 99.6 24.90 3.222 1 1111 1110 510 1FE 99.8 24.95 3.229 1 1111 1111 511 1FF 100.0 25 3.235 9.3.3 Select RIREF For a Given BC The maximum output current per channel, IOLCMax is determined by resistor RIREF placed between the IREF and IREFGND pins, and the BC code in FC register. The voltage on IREF is typically 1.209V. RIREF can be calculated by Equation 2. Riref(k Ω) = Viref(V) / IOLCMax(mA) × Gain (2) Where: VIREF = the internal reference voltage on IREF (1.209V, typical) IOLCMax is the largest current for each output at CCR/G/B=1FFh. Gain = the current gain at a selected BC code (See Table 2 ) Table 2. Current Gain Versus BC Code BC DATA RATIO OF GAIN GAIN / GAIN_MAX (AT MAX BC) BINARY HEX 000 (recommend) 0 (recommend) 20.0 12.9% 001 1 39.5 25.6% 010 2 58.6 37.9% 011 3 80.9 52.4% 100 (default) 4 (default) 100.0 64.7% 101 5 113.3 73.3% 110 6 141.6 91.7% 111 7 154.5 100% NOTE: Recommend to use smaller BC code for better performance. For noise immunity purposes, suggest RIREF < 60 kΩ. 9.3.4 Choosing BC/CC For a Different Application BC is mainly used for global brightness adjustment between day and night. Suggested BC is 4h, which is in the middle of the range; thus, one can change brightness up and down flexibly. CC can be used to fine tune the brightness in 512 steps, this is suitable for white balance adjustment between RGB color groups. To get a pure white color, the general requirement for the luminous intensity ratio of R, G, B LED is 3:6:1. Depending on LED’s characteristics (Electro-Optical conversion efficiency), the current ratio of R, G, B LED will be much different from this ratio. Usually, the Red LED will need the largest current. One can choose 511d(the max value) CC code for the color group which needs the largest current at first, then choose proper CC code for the other two color groups according to the current ratio requirement of the LED used. 14 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated |
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