MIC3289 Datasheet, PDF (10/13 Pages) Micrel Semiconductor – 1.2MHz PWM White LED Driver with Internal Schottky Diode and True 1-Wire Digital Control

Micrel, Inc.
MIC3289
as t_{PROG_LOW} and t_{PROG_HIGH} are not exceeded.
To maintain operation at the current brightness level
simply maintain a logic level high signal at the DC pin.
Figure 4. Mode Change to Count Up
To return the programming pulse counter to the Count-
Down Mode, apply a negative going pulse to the DC pin
with a period equal to t_{MODE_DOWN}. Now each pair of
programming pulses will cause the LED brightness to
decrease one level.
tMODE_DOWN
DC
MODE
COUNT DOWN
Figure 5. Mode Change to Count Down
Programming the Brightness Level
When it is powered up and the DC pin is at a logic level
high for greater than t_{START_UP}, the MIC3289 will begin
regulating LED drive current at the maximum brightness
level (Level 15). The internal control logic is set to
decrease the LED brightness upon receiving
programming pulses (falling edges of the DC input pin).
Applying a pair of clock signals as shown in Figure 6
below, decreases the brightness one level. Notice that
the first clock pulse is ignored. This is done so that Mode
Change pulses do not produce brightness changes. The
user may also elect to send a Mode Change as shown in
Figure 4 to set the MIC3289 to increment the brightness
level with subsequent programming pulses.
Figure 7. Decreasing Brightness Several Levels
As mentioned, the MIC3289 can be programmed to set
LED drive current to produce one of 16 distinct
brightness levels. The MIC3289s internal logic keeps
track of the brightness level with an Up/Down counter
circuit. The following section explains how the MIC3289s
brightness counter functions with continued
programming pulses.
Counter Roll-Over
The MIC3289 internal up/down counter counts from 0 to
15. When counting DOWN, and brightness level 0 is
reached, the counter will roll-over to level 15. This is
illustrated in Figure 8 below.
DC
tPROG_LOW
tPROG_HIGH
LEVEL n
BRIGHTNESS
LEVEL
PULSE
IGNORED
LEVEL n + 1
LEVEL n - 1
Figure 8. Down Counter Roll-over
When the counter Mode is set to count Up and
brightness level 15 is reached, the counter will roll-over
to level 0. Figure 9 shows that continuing to send
programming pulses will cause the brightness level to
start over at level zero.
Figure 6. Brightness Programming Pulses
Brightness programming pulses are not restricted to just
one pair at a time. Multiple level changes can be set as
shown in Figure 7 below. Just remember that the first
falling edge of the DC input clock will be ignored so long
March 2007
10
M9999-030407
[phone]