MIC2845A Datasheet, PDF (13/18 Pages) Micrel Semiconductor – High Efficiency 6 Channel Linear WLED Driver with DAM™, Ultra Fast PWM™ Control and Dual Low IQ LDOs

Micrel Inc.
MIC2845A
Figure 7. PWM Signal at 20% Duty Cycle (I_avg = 4mA)
Figure 10. PWM Signal at 100% Duty Cycle (I_avg = 20mA)
High Current Parallel Operation
Figure 8. PWM Signal at 50% Duty Cycle (I_avg = 10mA)
Figure 9. PWM Signal at 80% Duty Cycle (I_avg = 16mA)
Figure 11. Six Channel (Parallel) Application Circuit
The linear drivers are independent of each other and can
be used individually or paralleled to provide larger
current. A single LED can be driven with all 6 linear
drivers by connecting D1 through D6 together with the
cathode of the LED as shown in Figure 11. This will
generate a current 6 times the LED current setting and
can be used for higher current LEDs such as those used
in flash or torch applications. The current is set by the
R_SET resistor, and can be calculated by the following
equation.
I_LED (mA) = 6 * 410 * D / R_SET (kΩ).
D is the duty cycle of the LED current during PWM
dimming. When the device is fully on the duty cycle
equals 100% (D = 1). Figure 12 shows the response
time of the six paralleled linear drivers to the enable
signal, while Figure 13 shows the turn off response. With
a R_SET resistor of 1.65k, each linear driver is set to
250mA, with all 6 linear drivers connected in parallel, the
MIC2843 is capable of driving a total current of 1.5A.
April 2010
13
M9999-041210-C