MIC2860_D Datasheet, PDF (9/12 Pages) Micrel Semiconductor – High Efficiency 2 Channel WLED Driver with Single Wire Digital Control

Micrel Inc.
33µs (t_{START_UP}) after the SC pin is first pulled high at the
maximum brightness level 1. After start up, the internal
control logic is ready to decrease the WLED brightness
upon receiving programming pulses (positive edges
applied to SC pin). The brightness level can be
decreased one level by applying a single programming
pulse as shown in Figure 5. Brightness settings can be
quickly changed by sending programming pulses one
after each other. Each programming pulse has a high
(t_{PROG_HIGH}) and a low (t_{PROG_LOW}) pulse width that must
be between 0.3µs to 75µs.
MIC2860-2D
Counter Roll-Over
The MIC2860-2D internal counter contains registers
from 0 to 31 (32 levels). When the brightness level is at
32 (minimum brightness) and a programming pulse
forces the brightness to step down, the counter will roll-
over to level 31 (maximum brightness). This is illustrated
in Figure 7.
Figure 5. Brightness Programming Pulses
Multiple brightness levels can be changed as shown in
Figure 6. When issuing multiple brightness level
adjustments to the SC pin, ensure both t_{PROG_LOW} and
t_{PROG_HIGH} are within 0.3µs and 75µs.
To maintain operation at the current brightness level
simply maintain a logic level high at the SC pin.
Figure 7. Down Counter Roll-Over
Input Capacitor
The MIC2860-2D is a high performance, high bandwidth
device. Stability can be maintained using a ceramic input
capacitor of 1µF. Low ESR ceramic capacitors provide
optimal performance at a minimum amount of space.
Additional high-frequency capacitors, such as small
valued NPO dielectric type capacitors, help filter out high
frequency noise and are good practice in any noise
sensitive circuit. X5R or X7R dielectrics are
recommended for the input capacitor. Y5V dielectrics
lose most of their capacitance over temperature and are
therefore not recommended.
Figure 6. Consecutive Brightness Level Commands
The MIC2860-2D can be programmed to set WLED
drive current to produce one of 32 distinct brightness
levels. The following section explains how the brightness
counter functions with continued programming edges.
July 2010
9
M9999-072010-A