MIC2843 Datasheet, PDF (12/15 Pages) Micrel Semiconductor – High-Efficiency 6-Channel Linear WLED Driver with Ultra-Fast PWM™ Control

Micrel Inc.
High-Current Parallel Operation
The linear drivers are independent of each other, and
can be used individually or paralleled for larger current.
A single WLED can be driven with all six linear drivers by
connecting D1 through D6 together with the cathode of
the WLED as shown in Figure 11. This will generate a
current six times the LED current setting and can be
used for higher current WLEDs such as those used in
flash or torch applications.
MIC2843
Figure 12. Current Response Time to Enable Signal
Turning On (Six Paralleled Channels)
Figure 11. Six-Channel (Parallel) Application Circuit
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.
Figure 13. Current Response Time to Enable Signal
Turning Off (Six Paralleled Channels)
Input Capacitor
The MIC2843 is a high-performance, high-bandwidth
device. Stability can be maintained using a ceramic input
capacitor of 1µF. Low-ESR ceramic capacitors provide
optimal performance at a minimum amount of space.
Additional high-frequency capacitors, such as small-
valued NPO dielectric-type capacitors, help filter out
high-frequency noise and are good practice in any noise-
sensitive circuit. X5R or X7R dielectrics are
recommended for the input capacitor. Y5V dielectrics
lose most of their capacitance over temperature and are
therefore, not recommended.
November 2010
12
M9999-110810-B