MIC4811_1104 Datasheet, PDF (8/12 Pages) Micrel Semiconductor – High Current 6 Channel Linear WLED Driver with DAM™ and Ultra Fast PWM™ Control

Micrel Inc.
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 MIC4811 achieves
industry leading LED channel matching of 1% across the
entire dimming range.
Ultra Fast PWM™ Dimming Interface
The MIC4811 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 END pin. For PWM frequencies between 200Hz –
20kHz the MIC4811 supports a duty cycle range from
1% to 100%, see Figure3. The MIC4811 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 MIC4811 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 MIC4811 prior to
PWM dimming.
MIC4811
Figure 4. Channel Current Response to PWM Control
Signal Frequencies from 50kHz to 500kHz
Figure 5. Minimum Duty Cycle
for Varying PWM Frequency
Figure 3. Average Current per LED Dimming
by Changing PWM Duty Cycle for PWM Frequencies
up to 20kHz
April 2011
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M9999-041411-B