• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 62 subscribers
  • Views 87 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

LM5155: What is the minimum value of Cvcc?

Kazuya Nakai59
Guru 20100 points
Part Number: LM5155

Hello guys,

One of my customers is designing a power supply circuit using LM5155.

At this moment, they have the following questions. 

Could you please give me your reply for them?

Q1. What is the minimum value of Cvcc as actual capacitance value? The device datasheet says that the recommended VCC capacitor value is from 1 μF to 4.7 μF.

      Also TDK 1uF ceramic capacitor, GCM188R71C105MA64D is listed up as recommended parts.

      The capacitor has +/-20% variation in production and +/-15% variation in temperature range.

      So the minimum capacitance of the Cvcc is about 0.75uF. Can 0.75uF (Actual value) be used for Cvcc?

      What is the minimum actual value of Cvcc?  

Q2. Can a very small ESR ceramic capacitor be used for Cvcc. Is it no problem to use 1mohm ESR capacitor for Cvcc?

Your reply would be much appreciated.

Best regards.

Kazuya.

  • 0
    TI__Genius 11215 points

    Hello Kazuya-san, 

    Thanks for reaching out. We usually recommend ceramic capacitors with X7R dielectric for best temperature and voltage coefficient performance, low ESR is also a benefit of such capacitors. The datasheet recommendation already takes into account the tolerance of the capacitor, therefore I would not choose a value below the nominal recommended one with voltage rating of  16V or higher. 

    Kind regards, 

    EM

  • 0 in reply to EM
    Guru 20100 points

    Hello EM,

    Thank you very much for your reply.

    Could I ask you a few additional questions about COMP terminal voltage?

    (If I should ask it at new tread, please let me know.)

    Q1. What is the maximum output voltage of COMP terminal?

           I think GM amp which drives COMP terminal works with VCC voltage.

           VCC maximum voltage is 7V when VCC is not connected to VBIAS externally.

           So I think COMP terminal maximum voltage is 7V. Is my understanding correct? 

    Q2. If my understanding is correct, why the maximum voltage of Ccomp capacitor in datasheet and on EVM is 100V?

           Is 16V capacitor not enough?

    Thank you again and best regards,

    Kazuya. 

  • 0 in reply to Kazuya Nakai59
    TI__Genius 11215 points

    Hello Kazuya, 

    Thanks for your question. I would guess that in the EVM such a high voltage rating for the COMP caps was chosen due to availability issues. As you can see from section 9.3.8, page 22 and from the Electrical Characteristics table at page 7 "error amplifier -> COMP clamp voltage", the comp pin is a low voltage pin and a voltage rating of 16V is enough. Let me know if I can help you furthermore. 

    Kind regards, 

    Elisabetta