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LM5114: Questions about LM5114 output peak current and pullup resistance.

Kazuya Nakai59
Guru 20450 points
Part Number: LM5114
Other Parts Discussed in Thread: UCC27511A, UCC27511

Hello guys,

One of my customers is planning to replace UCC27511A with LM5114.
At this moment, they have the following questions. Could you please give me your reply for them?

Q1. Does LM5114 use the hybrid structure (PMOS+NMOS) for the high side SW placed between VDD-P_OUT same as UCC27511A?
Q2. LM5114 low side on resistance (0.23ohm typ) is lower than UCC27511A one (0.375ohm typ).
       But LM5114 sink peak current (7.6A typ) is lower than UCC27511A one (8A typ).
       What is the reason?
Q3. LM5114 Peak source current is 1.3A typ. I know this current is change depend on the high side MOS on resistance.
       If the high side MOS resistance become low, is it possible that LM5114 gets broken?
Q4. If LM5114 P_OUT/N_OUT driving capacitor become larger than 10nF, is it possible that LM5114 gets broken?
       Because I think LM5114 become hot in case of large capacitance driving. 
       What is the maximum capacitance which driven by P_OUT/N_OUT

Your reply would be much appreciated.

Best regards,

Kazuya.

  • 0
    TI__Expert 4070 points

    Hello Nakai-san,

    Thank you for reaching out!

    -------

    Here are my answers to your questions:

    1. No, LM5114 does not use a hybrid pull-up structure.
    2. The reason for different measurements is because they were tested under different test conditions.  They are tested at different VDD levels, and different current levels too.
    3. It depends.  As long as the driver is not dissipating too much heat/power, it should be fine.  This is dependent on the capacitance of the MOSFT you are driving and on the switching frequency.  With the peak source current being lower than most, you can likely use a gate resistor of a couple Ohms.
    4. It depends on the VDD, C_Load, and switching frequency.  The equations needed for this are in the "Power Dissipation" section of the datasheet.
      1. The UCC27511 also has a more thorough Power Dissipation section if you want to refer to that as well!

    -------

    I hope this helps and answers your questions!

    - Aaron

  • 0 in reply to Aaron Grgurich
    Guru 20450 points

    Hello Aaron,

    Thank you very much for your reply.

    The customer and I could understand LM5114 well because of your support.

    Thank you again and best regards,

    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Expert 4070 points

    You are welcome!  Glad I could help!

    - Aaron