MIC2845A Datasheet, PDF (12/18 Pages) Micrel Semiconductor – High Efficiency 6 Channel Linear WLED Driver with DAM™, Ultra Fast PWM™ Control and Dual Low IQ LDOs

Micrel Inc.
Application Information
Dynamic Average Matching (DAM™)
The Dynamic Average Matching architecture multiplexes
four current references to provide highly accurate LED
current and channel matching. The MIC2845A achieves
industry leading LED channel matching of 1.5% across
the entire dimming range.
Ultra Fast PWM™ Dimming Interface
The MIC2845A 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 applying a pulse width
modulated (PWM) signal to the END pin. For PWM
frequencies between 200Hz – 20kHz the MIC2845A
supports a duty cycle range from 1% to 100%, as shown
in Figure 3. The MIC2845A 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
MIC2845A 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, as shown in Figure 4 and Figure 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 PWM frequencies above}
15kHz require a logic high enable signal for 80μs to first
enable the MIC2845A prior to PWM dimming.
MIC2845A
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
Figure 6. PWM Signal at 1% Duty Cycle (I_avg = 0.2mA)
April 2010
12
M9999-041210-C