MIC2843 Datasheet, PDF (10/15 Pages) Micrel Semiconductor – High-Efficiency 6-Channel Linear WLED Driver with Ultra-Fast PWM™ Control

Micrel Inc.
Application Information
Ultra Fast PWM™ Dimming Interface
The MIC2843 can receive PWM signals from the END
pin for WLED dimming. Dimming is generated by pulsing
the WLEDs on and off in synchronization with the PWM
signal. The MIC2843 supports PWM frequencies from
200Hz to 500kHz. For PWM frequencies between 200Hz
– 20kHz the MIC2843 supports a duty cycle range from
1% to 100%. The MIC2843 supports Ultra Fast PWM™
frequencies from 20kHz to 500kHz with a duty cycle of
10% and greater. MIC2843 incorporates an internal
shutdown delay to ensure that the internal control
circuitry remains active during PWM dimming for
optimum Ultra Fast PWM™ performance. Due to input
PWM signal propagation delay Ultra Fast PWM™
signals have a non-linear relationship between the duty
cycle and the average LED current (Figures 3 and 4).
With the Ultra Fast PWM™ frequencies, lower duty
cycles may degrade the matching between LEDs, and
should be limited to the minimum duty cycle, as
indicated in Figure 5. Due to the shutdown-to-on delay of
60µs, at Ultra Fast PWM™ frequencies above 15kHz, a
logic high enable signal is required to first wake up prior
to PWM dimming. Figures 6 through 10 illustrate the
WLED current response when a PWM signal is applied
to the END pin.
MIC2843
Figure 3. Average Current per LED Dimming by Changing
PWM Duty Cycle for PWM Frequencies up to 20kHz
Figure 4. Average Current per LED Dimming by Changing
PWM Duty Cycle for PWM Frequencies from 50kHz to
500kHz
November 2010
Figure 5. Minimum Duty Cycle for Varying PWM
Frequency
10
M9999-110810-B