MS03a-22 Design of Buck Regulator IC

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ZHENG, Zheyang
January 18, 2023 2:32 pm
  1. What is the relation between CCM and stable output?
  2. You mentioned 3rd Type compensation is complicated. Why is it essential in your design?
  3. Have you changed the load to verify the “stable output regardless of the load impedance”?
  4. Is it normal to use pMOS in the power stage? Pros and Cons?
KIM, Seonghyun
January 18, 2023 3:11 pm
Reply to  ZHENG, Zheyang

Thank you for the question Prof. Zheng,

-CCM is an abbreviation of the term “Continuous Current Mode” and it means that the inductor in LC filter will always conducting in the steady-state operation. Compared to that, DCM is another name of “Discontinuous Current Mode” which means that the inductor is not always conducting its current. In these term, CCM and DCM are the two ways of operating the buck converter ,and the stable output can be generated in any of these two operation modes. The reason that CCM is chosen is that it provides better overall efficiency under the lower duty cycle (out design has low duty cycle value which is less than 0.5), and stable output is actually depends on the values of LC which attenuates the ripple output voltage and its whole closed loop gains but not depends on the mode of operations.

-The 3rd type compensation is complicated since it provides the two extra poles and zeros on its error amplifier open loop, which makes the designer harder to construct it. However, the phase drop occurs on the “voltage-controlled” type buck converter is significant, and the 3rd compensator can provides the large phase enhancement more than 90 degrees compared to the 2rd compensator to strongly compensate the significant drop in the phase.

-Not yet. We have decided the topologies and did the hand calculation processes in the previous semester. However as professor said, the various load must be tested in the simulation process which is planned to be done in the next semester.

-usage of PMOS is essential in our 1st power transistor, because this transistor will be used to pump the input power to the load. If NMOS is used instead, the switch will only charges the inductor to the value of (input voltage – NMOS threshold voltage.)
Of course, Con also exists. The hole mobility of PMOS is lower than NMOS, so that the (W/L) ratio of PMOS will be very high, so that it charges a lot of space. This part is quite critical in IC designing process which requires us to minimize the IC chip as much as possible.

Again, appreciated sir!