MIC2298_11 Datasheet, PDF (9/13 Pages) Micrel Semiconductor – 3.5A Minimum, 1MHz Boost High Brightness White LED Driver

Micrel, Inc.
Figure 7. LED Current vs. DC (on BRT pin)
Should the SS/DIM pin be used for voltage programming
the LED current, note that there will be a small offset due
mismatches between the 30k FB input and the
impedance driving the SS/DIM pin.
Soft Start Functionality
The soft start time is dependant up on both C_SS and the
comp capacitor values. C_COMP is fixed for stable
operation (typically 33nF); therefore, if any increases in
soft start are desired, this should be done using the C_SS
capacitor. The approximate total startup time is given by
the larger of: -
T_SS = 1ms + 175k ⋅ C_SS
Or
T_SS = 1ms + C_COMP / 44 ⋅ 10 ^−6
E.g. for C_COMP = 33nF, use values of C_COMP > 4.3nF to
increase startup time from 1.75ms. The soft start
capacitor should be connected from the SS/DIM pin to
ground.
MIC2298
October 2007
9
M9999-101707-B