About the calculation formula of MP1476 RT resistance value

Dear support member,

I plan to use MP1476.

(The specification conditions)

There is no description of Rt setting in the data sheet.
How do you determine the constant?
Is there a calculation formula?

Best regard.

Well there is a table showing Rt decreasing as Vout rises. Maybe draw a graph of Rt vs Vout and extend that line/curve to 8V as a starting guess. Hopefully it works, then try double the value and half the value to see if it still works. Maybe change it a whole bunch to see what goes wrong?

Looking at the block diagram ( which of course leaves out details) I don’t see a particular reason for it.

Hi hideyuki_okada,

The RT resistor affects the loop stability. Using a small RT, the loop bandwidth would be high but the phase margin would be low and may lead to instability. As shown in Table 1 and Table 2, the size of the inductor and output capacitors will also affect loop stability and the size of FB network resistors. The RT value is decided by testing the bode plot of the system and aiming to keep the phase margin above 45 degrees. For your system, I would suggest using an RT value between 0-20k and adjust accordingly.

Hi, bryan.

Thank you very much for your answer.

Best regard.