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LMG3522R050: Need VNEG current vs Switching Frequency graph

Sundar Raj A
Prodigy 71 points
Part Number: LMG3522R050


Tool/software:

Please share the graph for VNEG current vs Switching Frequency, Thank You

  • 0
    TI__Expert 8553 points

    Hi Sundar,

    Using the same equation from the other thread:

    IVdd = Ivvd +Fsw*k + Igate*D

    Igate ~ 0 for LMG3522.

    k = (Ivdd-Ivddq)/Fsw

    From datasheet values k can be calculated.

    Then Vdd vs Fsw curve can be created.

    Once we have, VDD current vs frequency. About 90% of the power for the gate drive is consumed from the VNEG rail. So, and the VNEG buck-boost is about 70% efficient. So you can translate the power consumed from the VDD rail to the power consumed on the VNEG rail by P_NEG = P_VDD*0.9*0.75. Then divide P_NEG by 14V to get the current.

    To answer your question, the current is directly proportional to the frequency since all the gate drive charge comes from that rail.

    Best,

    Pratik A.

  • 0
    Prodigy 71 points

    Thank you for sharing this information

  • +1
    Prodigy 71 points

    Thank you for sharing the information. I have three more questions:

    1. If I supply power only to VDD and VNEG is internally connected, how can I measure the current on VNEG?

    2. If I provide an external negative voltage to VNEG, how can I calculate the current flowing through VNEG?

    3. In this case, the thermal pad of the MOSFET acts as the source, right? Can the all source be connected externally? If it is connected, what will happen?

  • +1 in reply to Sundar Raj A
    TI__Expert 8553 points
    Sundar Raj A said:
    If I supply power only to VDD and VNEG is internally connected, how can I measure the current on VNEG?

    In this case the VDD operating current would be the Vneg current. 

    Sundar Raj A said:
    If I provide an external negative voltage to VNEG, how can I calculate the current flowing through VNEG?

    They need to remove the buck boost inductor and supply -14.5 externally and can measure that current from the supply

    Vneg is generated internally, no need to provide external voltage or supply.

    Sundar Raj A said:
    In this case, the thermal pad of the MOSFET acts as the source, right? Can the all source be connected externally? If it is connected, what will happen?

    Yes, thermal pad always acts like a source as it's internally connected to the source.

    Hope these helps.

    Best,

    Pratik A.