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MIC4812 Datasheet(PDF) 8 Page - Micrel Semiconductor |
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MIC4812 Datasheet(HTML) 8 Page - Micrel Semiconductor |
8 / 12 page Micrel Inc. MIC4812 April 2011 8 M9999-041419-B Application Information Dynamic Average Matching (DAM™) The Dynamic average matching architecture multiplexes four voltage references to provide highly accurate LED current and channel matching. The MIC4812 achieves industry leading LED channel matching of 1% across the entire dimming range. Ultra Fast PWM™ Dimming Interface The MIC4812 supports a wide range of PWM control signal frequencies from 200Hz to 500kHz. This extremely wide range of control provides ultimate flexibility for handheld applications using high frequency PWM control signals. WLED dimming is achieved by pulse width modulating the linear drivers which are controlled by a PWM signal to the EN pin. For PWM frequencies between 200Hz – 20kHz the MIC4812 supports a duty cycle range from 1% to 100%, see Figure 3. The MIC4812 incorporates an internal shutdown delay to ensure that the internal control circuitry remains active during PWM dimming. This feature prevents the possibility of backlight flickering when using low frequency PWM control signals. The MIC4812 also supports Ultra Fast PWM™ frequencies from 20kHz to 500kHz. Due to input signal propagation delay, PWM frequencies above 20kHz have a non-linear relationship between the duty cycle and the average LED current, see Figures 4 and 5. Figures 6 through 10 show the WLED current response when a PWM signal is applied to the END pin (1). (1) From the low Iq sleep mode higher PWM frequencies may require a logic high enable signal for 60μs to first enable the MIC4812 prior to PWM dimming . Figure 3. Average Current per LED Dimming by Changing PWM Duty Cycle for PWM Frequencies up to 20kHz Figure 4. Channel Current Response to PWM Control Signal Frequencies from 50kHz to 500kHz Figure 5. Minimum Duty Cycle for Varying PWM Frequency |
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