I am in the middle of a project where i want to use a mcu (ST32F3028U6 with DAC of 2.4V - 3.6V) to control the V_out voltage of a LT8494 SEPIC DC/DC Converter. I understand the basic operation of the converter and the purpose of some of the components in the application example.
I have also included a snippet from the LT8494 datasheet
In my case V_in is from a 1S Li-Po, so approx. 3.0 - 4.2 V
I understand completely the functions of and the external components belonging to pins V_in, SWEN, SS, PG, GND.
What i am having trouble with is the circuitry in the upper area of the picture. Hence, the question of this post is: What is the purpose of the circuitry in the upper section of the snippet (including components D1-D4 etc), what is the purpose of BIAS and FB pins and how do i choose the correct resistor values R1, R2, R3 (in the picture 1M, 78,7k and 26.7k) to be able to control the output voltage with the DAC of my MCU
My current understanding of the circuit is as follows: Please correct me if I am wrong at any of the following aspects/explanations
When the NPN in the SW pin is enabled the current from Vin is stored in L1 and when the NPN is disabled the current is discharged through C3 to the output, generating the desired output voltage using R1, R2, R3. I dont understand the effect of L2 and the rack of diodes and capacitors.
Sorry for the long post, i was trying to be thorough in my explanation of the problem. Any help is greatly appreciated
EDIT: My desired output voltage would be in the range of approx 1.3V - 12V