FAN5333A Datasheet, PDF (9/11 Pages) Fairchild Semiconductor – High Efficiency, High Current Serial LED Driver with 30V Integrated Switch

3. Dimming Using Filtered PWM Signal
This method allows the use of a greater than 1kHz PWM fre-
quency signal with minimum impact on the battery ripple. The
filtered PWM signal Table 8 on page 9 acts as an adjustable DC
voltage as long as its frequency is significantly higher than the
corner frequency of the RC low pass filter.
FAN5333A
FB
20KΩ 15KΩ
1.6KΩ
5Ω
0.1µF
FAN5333B
FB
20KΩ ^15KΩ
4.7KΩ
15Ω
0.1µF
Thermal Shutdown
When the die temperature exceeds 150°C, a reset occurs and
will remain in effect until the die cools to 130°C, at that time the
circuit will be allowed to restart.
PCB Layout Recommendations
The inherently high peak currents and switching frequency of
power supplies require careful PCB layout design. Therefore,
use wide traces for high current paths and place the input
capacitor, the inductor, and the output capacitor as close as
possible to the integrated circuit terminals. The FB pin connec-
tion should be routed away from the inductor proximity to pre-
vent RF coupling. A PCB with at least one ground plane
connected to pin 2 of the IC is recommended. This ground plane
acts as an electromagnetic shield to reduce EMI and parasitic
coupling between components.
Figure 8. Dimming Using Filtered PWM Signal
9
FAN5333A/FAN5333B Rev. 1.0.1
www.fairchildsemi.com