I have designed an SMPS circuit for my host board. As the datasheet, the feedback resistors are calculated as
As per the datasheet, Feedback Voltage(Vref) is 0.6V and I want 4V Output Voltage. Therefore, feedback resistors are chosen like below after the calculation.
R15 = 5.6K
R17 = 1K
I measured the output voltage from the board; it is 1.2V.
I also measured the feedback voltage and it is 0.6V, same as in the datasheet. So, what can be the problem? Am I doing something wrong? Calculations were done with an oscilloscope.
(I can not add the datasheet link as I don't have enough reputation. The SMPS regulator is L7986 from STmicroelectronics.)
Update1: I changed feedback resistors to get the 4V output by changing the resistors ratio. Measured output was 1.2V with initial resistors. So I changed the resistor rate by multiplying it with 2.3 (4/1.2V) to get 4V output. After this change, the output voltage is about 7.8V. I had thought that I can get the desired output voltage if I modify the ratio of feedback resistors. So, any thoughts?
Update2: I guess I broke the regulator while trying to measure the output voltage with an oscilloscope. I don't know what caused this, but now the regulator outputs the input voltage directly to the output pin. I was very careful with the connections, I just connected it to voltage supply as the same before and measured voltages from the scope.