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LM5175: External VCC? Ground-referencing high-side drivers?

Paul Shepherd17
Intellectual 595 points

Part Number: LM5175

I am interested in using the LM5175 to drive GaN half bridges that have built-in high and low-side drivers (FBS-GAM02-P-C50). The maximum allowable voltage on the half-bridge control inputs is 5V, and I have a 5V supply on my board already. Is it acceptable to drive the LM5175 VCC pin with 5V, and not rely on the LDOs from the VIN and BIAS pins? (leave them unconnected) This would keep the output voltages on the LDRV and HDRV pins in the 0-5V range.

There is a second question, which relates to tying the High-side driver reference pins (SW1 and SW2) to ground. The FBS-GAM02-P-C50 already has a level shifter built into it, so the high-side outputs of the LM5175 do not need to be tied to the switching nodes for generating the proper gate voltages. Is it okay to tie the SW1 and SW2 pins on the LM5175 to ground, or are those pins used for some type of sensing/control other than level shifting the high-side driver outputs?

Thanks,

Paul

  • 0
    TI__Guru 72155 points

    Hello Paul,

    I never used the device with just VCC connected. So my first reaction would be to recommend connecting VIN as well to the 5V.

    I would at least create the first board with the ability to connect SW1 and SW2 to both sides of the inductor as these do have some sensing features attached to them, e.g. for DCM operation.

    As I did not find the time to check this out myself, I am curious about your experience.

    Best regards,
    Brigitte

  • 0
    Intellectual 595 points

    Hi Brigitte,

    That makes sense on trying VIN and VCC to the 5V rail. 

    As for tying SW1 and SW2 to ground, it sounds like it's less likely to cause an issue as long as the LM5175 is running in CCM mode?

    Thanks,

    Paul

  • 0 in reply to Paul Shepherd17
    TI__Guru 72155 points

    Hello Paul,

    Most probable, but as mentioned, I would recommend to have the ability to connect them to the switch nodes in case it is needed.

    Best regards,
    Brigitte