MIC2846A Datasheet, PDF (14/19 Pages) Micrel Semiconductor – High Efficiency 6 Channel Linear WLED Driver with DAM™, Digital Control and Dual Low IQ LDOs

Micrel Inc.
Count Up Mode until its mode is changed to Count Down
Mode or by disabling the MIC2846A to reset the mode
back to default.
MIC2846A
Figure 8. Mode Change to Count Up
To change the mode back to Count Down Mode, pull the
DC pin low for a period equal to t_{MODE_DOWN} (420µs to
500µs), shown in Figure 9. Now the internal circuitry will
remain in Count Down Mode until changed to Count Up
as described previously.
Figure10. Brightness Programming Pulses
Multiple brightness levels can be set as shown in Figure
11. When issuing multiple brightness level adjustments
to the DC pin, ensure both t_{PROG_LOW} and t_{PROG_HIGH} are
within 2µs to 32µs.
To maintain operation at the current brightness level
simply maintain a logic level high at the DC pin.
Figure 9. Mode Change to Count Down
Programming the Brightness Level
MIC2846A is designed to start driving the LEDs 140µs
(t_{START_UP}) after the DC pin is first pulled high at the
maximum brightness level of 48. After start up, the
internal control logic is ready to decrease the LED
brightness upon receiving programming pulses (negative
edges applied to DC pin). Since MIC2846A starts in
Count Down Mode, the brightness level can be
decreased without a mode change by applying two
programming pulses, as shown in Figure10. Note that
the extra pulse is needed to decrease brightness
because the first edge is ignored. Anytime the first falling
edge occurs later than 32µs after a Mode Change, it will
be ignored. Ignoring the first falling edge is necessary in
order that Mode Change (t_{MODE_UP}, t_{MODE_DOWN}) pulses do
not result in adjustments to the brightness level. Each
programming pulse has a high (t_{PROG_HIGH}) and a low
(t_{PROG_LOW}) pulse width that must be between 2µs to
32µs. The MIC2846A will remember the brightness level
and mode it was changed to. For proper operation,
ensure that the DC pin remains high for at least t_DELAY
(140µs) before issuing a mode change command.
Figure11. Decreasing Brightness Several Levels
As mentioned, MIC2846A can be programmed to set
LED drive current to produce one of 49 distinct
brightness levels. The internal logic keeps track of the
brightness level with an Up/Down counter circuit. The
following section explains how the brightness counter
functions with continued programming edges.
Counter Roll-Over
The MIC2846A internal up/down counter contains
registers from 0 to 48 (49 levels). When the brightness
level is at 0 and a programming pulse forces the
brightness to step down, then the counter will roll-over to
level 48. This is illustrated in Figure 12.
April 2010
Figure 12. Down Counter Roll-Over
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