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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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FAN5616 Fiches technique(PDF) 11 Page - Fairchild Semiconductor |
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FAN5616 Fiches technique(HTML) 11 Page - Fairchild Semiconductor |
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11 / 14 page  11 www.fairchildsemi.com FAN5616 Rev. 1.0.0 2. Digital Control A built-in 2-bit DAC is used to digitally control the LED’s brightness through the EN1 and EN2 inputs. Once the desired maximum LED current is set by the external RSET resistor, the percentage of the maximum LED cur- rent is selected, as described in Table 2, to perform the dimming operation. Table 2. LED Dimming with Internal 2-bit DAC 3. PWM Control In addition to the digital LED brightness control, the FAN5616 features a PWM control. The LED current var- ies according to the width of the PWM signal applied to the EN1/EN2 input pins. Once the desired maximum LED current (ILED-MAX) is set by the external RSET resis- tor, the percentage of ILED-MAX to perform the dimming operation depends on the configuration of the PWM sig- nal with respect to the 2-bit DAC inputs (EN1 and EN2) as described in Table 2. For example, if RSET = 7.8kΩ then ILED-MAX = 20mA. If EN1 and EN2 are tied together and a PWM signal is applied, the LED current will vary between 0% and 100% (0mA and 20mA) of the maximum LED current according to the duty cycle of the PWM signal. The PWM signal can be applied to either enable input pins (EN1/EN2) or to both tied together. Depending upon the configuration, the average LED current can be adjusted within any range limited by 0, 1/3, 2/3, 3/3 of the maximum LED current as described in Table 3. The PWM duty cycle is assumed to be between 10% and 90%. Table 3. Average LED Dimming Range The recommended PWM frequency range is 200Hz to 50kHz for an acceptable linear response. At higher frequencies, the current waveform can no longer follow the PWM signal waveform, resulting in a significant difference between the value of the average ILED and the theoretical calculation. Figure 7. Ideal PWM Dimming Response 4. Dimming with DC Voltage The brightness control using a variable DC voltage is shown in Figure 8. If R1 = 78k Ω, R2 = 7.8kΩ, adjusting VEXT in the 0V to 0.6V range results in dimming the LED current from 22mA to 2mA. Figure 8. DC Voltage Control The FAN5616’s internal circuit maintains a constant VSET = 0.6V. Adjusting VEXT changes the ISET and ILED accordingly. By selecting different values for R1, R2 and VEXT, the ILED variation range can be changed according to the fol- lowing equation: Where, 0V < VEXT < 0.6V (1+R2/R1) and R1 and R2 are in k Ω. EN2 EN1 LED Current % of Maximum 00 0% 01 33.3% (1/3) 10 66.7% (2/3) 11 100% (3/3) Enable Input Pins Average ILED Adjustment Range EN2 EN1 LOW TOGGLE 3% to 30% of ILED-MAX HIGH TOGGLE 70% to 97% of ILED-MAX TOGGLE LOW 6% to 60% of ILED-MAX TOGGLE HIGH 39% to 93% of ILED-MAX TOGGLE TOGGLE 10% to 90% of ILED-MAX 50 100 50 100 0 0 PWM Signal Duty Cycle (%) R1 R2 FAN5616 VEXT ISET () mA 2 R x V – 260 156 1 R 156 I EXT LED + = |
Numéro de pièce similaire - FAN5616 |
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Description similaire - FAN5616 |
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