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Original question:

LM5116: Could LM5116 start up when output is already have a 50V votage.

LM5116: About LM5116 applicaiton

Gabriel Wang1
Genius 4725 points
Part Number: LM5116
Other Parts Discussed in Thread: UCC27714, , LM5146

Dear Expert

Our operation condition is :Input 73~80VDC, output 71.5/20A.

At present, there are some problems with insufficient driver of LM5116. Totem pole was added before. Now we want to add half bridge driver chip UCC27714 between LM5116 and MOS.

Our current schematic diagram is as follows, may I ask how to connect it? Can THE SW pin of LM5116 be disconnected?Or is the SW foot connected to the HS foot of UCC27714?We do not plan to connect the HB of LM5116 to UCC27714, which will have separate power supply.

Please confirm whether this is feasible and how to connect the SW foot?

  • 0
    TI__Guru 74572 points

    Hi Gabriel,

    This seems excessively complicated. Take a look at the LM5146 100V controller if you need more drive capability.

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Genius 4725 points

    Dear Expert

    1：Adjustable output voltage from 0.8 V to 60 V

    ----LM5146 has a maximum output of 60V, ours has a maximum output of 72V, which cannot be satisfied.

    2: the problem we are facing now is that the original circuit with 12V power supply will break down LM5116;If we remove the external power supply and use the 7.4V power supply inside the chip, the driving voltage will only be 5V (G pole of MOS), the driving voltage is not enough, and the pit will fall, so we want to add a half bridge drive.

    If there is no better recommendation, please reply to my following questions:

    3.Please confirm the following reply:

    At present, there are some problems with insufficient driver of LM5116. Totem pole was added before. Now we want to add half bridge driver chip UCC27714 between LM5116 and MOS.

    Our current schematic diagram is as follows, may I ask how to connect it? Can THE SW pin of LM5116 be disconnected?Or is the SW foot connected to the HS foot of UCC27714?We do not plan to connect the HB of LM5116 to UCC27714, which will have separate power supply.

    Please confirm whether this is feasible and how to connect the SW foot?

  • 0 in reply to Gabriel Wang1
    TI__Guru 74572 points

    Hi Gabriel,

    Can you use lower gate charge 100V FETs? 150V FETs should not be required for a 100V controller as the SW voltage is effectively limited to 100V. Just make sure that the DC current from VCC to drive the FETs is less than the VCC current limit (15mA min, 26mA typ), where Igate for each FET is Qg*Fsw.

    If you use an external driver and the SW voltage is < 100V, then it's okay to connect it to the controller (this keeps SW voltage sensing for deadtime control and zero-cross detection).

    Regards,

    Tim