MIC2289C Datasheet, PDF (8/10 Pages) Micrel Semiconductor – White LED Driver Internal Schottky Diode and OVP

Micrel, Inc.
Start-Up and Inrush Current
V_IN
During start-up, inrush current of approximately double
the nominal current flows to set up the inductor current
and the voltage on the output capacitor. If the inrush
current needs to be limited, a soft-start circuit similar to
Figure 5 could be implemented. The soft-start capacitor,
CSS, provides over-drive to the FB pin at start-up,
resulting in gradual increase of switch duty cycle and
limited inrush current.
VIN SW
OUT
EN
FB
GND
MIC2289C
2200pF
C_SS
R 10k
Figure 5. One of Soft-Start Circuit
6-Series LED Circuit without External Soft-Start
L = 10µH
C_IN = 1µF
C_OUT = 0.22µF
V_IN = 3.6V
I_OUT = 20mA
6 LEDs
TIME (100µs/dvi.)
Figure 6. 6-Series LED Circuit
without External Soft Start
6-Series LED Circuit with External Soft-Start
L = 10µH
C_IN = 1µF
C_OUT = 0.22µF
V_IN = 3.6V
I_OUT = 20mA
6 LEDs
C_SS = 2200pF
TIME (100µs/dvi.)
Figure 7. 6-Series LED Circuit
with External Soft Start
September 2006
8
M9999-090706