Selecting a ripple current when DC current is required through the LED string

Question: Why do I need to select a ripple current when I want DC current through the LED string?

 

Answer:

The PowerPSoC uses hysteretic control to regulate the LED string current. The control loop formed by the hysteretic control requires a minimum response time between current measured and output adjust so 0% current ripple is not possible. A small ripple current will result in a high switching frequency and higher system-level power loss; a larger ripple current will result in lower switching frequency and better system efficiency. A very large ripple current will result in visible flicker or pulsing of the LEDs, so a good ripple current will be 20-30% of the desired average output current. An example is 1A output current average, 20% ripple is 200mA current ripple. The output current will swing between 1.1A and 0.9A with the average at 1A.