Tool/software: WEBENCH® Design Tools
I am using the LM3492 to drive 2 strings of 9 LEDs per string. the LED Vf is 3.2volts and string voltage is 28.8V
Input power is 12VDC. The current is 20mA per string
The Webbanch gave me a design with inductor value of 120uH, Rf1= 402K, Rf2=16.2K, Rrt-226K. I made a sanity check based on the formulas of the LM3492 datasheet
1. I see that the Inductor value is too big. 120uH inductor causes too low switching frequency. Based on the formulas provided by the datasheet (paragraph 9.2.2.2), 12uH looks more logical
2. if Rf2 is 16.2K, and Rrt= 226K ->Rf1 should be 170K. (paragraph 8.3.8 - calculate output voltage)
Where is my mistake?