This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LP8866-Q1: About Rfb4 and Ccomp

Part Number: LP8866-Q1

Hi All,

I have a question about LP8866-Q1.

How do you set the values for the resistor Rfb4 and the capacitor Ccomp, referring to the schematics on the "Figure 8-5" ?
There was no specific value or calculation method in the data sheet.

What are the values for Rfb4 and Ccomp? Or, please tell me the calculation method.

Best Regards,
Ishiwata

  • Ishiwata, 

    Please refer to description in 7.3.6.3.3 FB Divider Using External Compensation

    Usually Rfb4 and Ccomp are not needed for application as LP8866 has internal compensation network to keep the DC-DC control loop in good stability in most cases. 

    Regards, 

    Xiaoguang 

  • Xiaoguang,

    Thank you for your reply.

    The data sheet has the following description.

    "And boost external compensation is used to compensate the removal of the 33-µF Al-polymer electrolytic capacitor. "


    Is it okay to understand that the resistor Rfb4 and the capacitor Ccomp do not have to be connected without Al-polymer electrolytic capacitor?

    Best Regards,
    Ishiwata

  • Ishiwata

    On the contrary, esistor Rfb4 and the capacitor Ccomp might need to be connected where there is no Al-polymer electrolytic capacitor.

    Regards, 

    Xaioguang 

  • Xiaoguang

    I have been asking questions about in the case there is no Al-polymer electrolytic capacitor.

    In the case there is no Al-polymer electrolytic capacitor,
    do the values of resistor Rfb4 and capacitor Ccomp refer to 7.3.6.3.3 FB Divider Using External Compensation?
    Or, if you have any reference values such as specific values of Rfb4 and Ccomp, please let me know.

    Best Regards,
    Ishiwata

  • Ishiwata, 

    Yes, the values can refer to 7.3.6.3.3 FB Divider Using External Compensation. 

    It depends on power stage design(Inductor/output capacitance)  and R1 & R2 value. you may start with 470k+ 470pF and then fine tune the parameter according to application. 

    Regards, 

    Xiaoguang