MIC2844A Datasheet, PDF (11/14 Pages) Micrel Semiconductor – High Efficiency 6 Channel WLED Driver with DAM™ and Single Wire Digital Control

Micrel Inc.
MIC2844A
(2µs to 32µs). Figure 15 illustrates the proper timing for
execution of a One-Step Brightness Increase.
Figure 12. Down Counter Roll-Over
Similarly, when the counter mode is set to Count Up and
a programming pulse forces the brightness level to step
up from level 48, then the counter will roll-over to level 0
as illustrated in Figure 13.
Figure 13. Up Counter Roll-Over
One-Step Brightness Changes
The “One-Step” brightness change procedure relieves
the user from keeping track of the MIC2844A’s up/down
counter mode. It combines a Mode Change with a
programming edge; therefore, regardless of the previous
Count Mode, it will change the brightness level by one.
Figure 15. One-Step Brightness Increase
Presetting Brightness
Presetting the brightness will allow the MIC2844A start-
up at any brightness level (0 to 48). The MIC2844A does
not turn on the linear LED driver until the DC pin is kept
high for t_{START_UP} (140µs). This grants the user time to
preset the brightness level by sending a series of
programming edges via the DC pin. The precise timing
for the first down edge is between 5µs to 75µs after the
DC pin is first pulled high. The 70µs timeframe between
5µs and 75µs is the t_{PROG_SETUP} period. The first
presetting pulse edge must occur somewhere between
the timeframe of 5µs to 75µs, otherwise the MIC2844A
may continue to start up at the full (default) brightness
level.
Figure 14. One-Step Brightness Decrease
The One-Step Brightness Decrease method is quite
simple. First, the DC pin is pulled low for a period equal
to the t_{MODE_DOWN} (420µs to 500µs) and immediately
followed by a falling edge within t_{PROG_HIGH} (2µs to 32µs)
as shown in Figure 14. This will decrease the brightness
level by 1. Similarly a One-Step Brightness Increase can
be assured by first generating a DC down pulse whose
period is equal to the t_{MODE_UP} (100µs to 160µs) and
immediately followed by a falling edge within t_{PROG_HIGH}
Figure 16. Presetting Timing
Figure 16 shows the correct presetting sequence to set
the MIC2844A brightness to level 39 prior to start up.
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 t_{PROG_HIGH} and t_{PROG_LOW} pulse width must
still be between 2µs to 32µs.)
August 2009
11
M9999-080309-D