Cirrus Logic AN368 - Manual (Page 62)

AN368
62 AN368REV2
Design Tip - Frequent re-syncing events on the second stage
Symptoms:
The current in either channel keeps changing by 1mA to 3mA in either direction and
does not stay fixed. Attaching a current probe on the output shows random large
droops in the red channel current waveforms (cyan) as shown below or non-steady
behavior in the blue-white current (purple). The droops will span across multiple
switching cycles if they are triggered by a re-sync event.
Cause: The reason for these output current deviations is most likely due to malfunctioning
of the Synchronizer Circuit. The most likely cause of this is noise on the clock input
of the Synchronizer Circuit D flip-flop.
Solution: This problem can be solved by a better designed RC filter on the D input of the flip-
flop. Refer to the Synchronizer Circuit RC Filter Design section on page 35 for
recommendations to solve this problem.
Step 7) Color System Parameters
The LED system design for the CS1630 driver was done using a simplified modeling procedure using LEDs
that were characterized in the integrating sphere. The basic specifications governing the light system design
are as follows:
1. Color temperature at full brightness = 2700k
2. Decrease color temperature as the conduction angle is reduced
Figure 22. Second-stage Synchronizer Circuit with RC Filter