Micrel, Inc.
MIC3291
Figure 12 shows the correct presetting sequence to set
the MIC3291 brightness to Level 6 prior to startup. The
sequence is initiated by driving the DC pin LOW for a
period exceeding t
SHUTDOWN
(1260µs) to insure that the
part has entered the power saving shutdown state
erasing all brightness level state and mode setting. Then
the DC pin is driven HIGH and the first presetting pulse
edge is entered within the t
PROG_SETUP
window. Notice
that when using the presetting feature the first
programming pulse is not ignored. This is because the
counter’s default mode is count down and a mode
change cannot be performed in the presetting mode.
(Note that the same timing requirements of standard
brightness programming also apply during presetting
brightness.)
Figure 11. One step Brightness Increase
Presetting Brightness
The brightness level can be preset before the MIC3291
begins to drive the LEDs by sending a series of
programming edges via the DC pin during the t
START_UP
(140µs) period and between 35µs to 50µs after the DC
pin is first pulled HIGH. The 15µs timeframe between
35µs and 50µs is the t
PROG_SETUP
period. The MIC3291
does not drive current into the load until DC pin is kept
HIGH for t
START_UP
(140µs) after presetting has concluded
in order to grant the user sufficient time to preset LED
brightness. The first presetting pulse edge must occur
somewhere between the timeframe of 35µs to 50µs after
DC pin is first pulled HIGH otherwise the MIC3291 may
continue to start at the full (default) brightness level.
Figure 12. Preset Timing
September 2010
12
M9999-092810
(408) 944-0800
MICREL [ MICREL SEMICONDUCTOR ]
