Micrel Inc.

MIC2860-2D

July 2010

9

M9999-072010-A

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

be between 0.3µs to 75µs.

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 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 5. Brightness Programming Pulses

Multiple brightness levels can be changed as shown in

Figure 6. When issuing multiple brightness level

To maintain operation at the current brightness level

simply maintain a logic level high at the SC pin.

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.