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LM5161: VCC Bias

Stefano Infante
Expert 2320 points
Part Number: LM5161

Hello!

I am working (again...) with LM5161; in my previous designs I always had a 10 V line to use as a bias for the VCC regulator, but this time I have not.

My input is about 48V and output is 24V (flybuck topology); the current should be about 0.6 A. Does it make sense to add an LDO to the 24V output in order to bias VCC? I would avoid using a buck converter just for that reason, but I don't like the low efficiency of the internal VCC regulator. Using a linear regulator could let me save about 50% (24V/48V) of the VCC regulator current, but I have to decide if it's worth it.

How much current is drawn by VCC in typical conditions?

Thanks in advance.

Regards,

Stefano

  • 0
    TI__Mastermind 39980 points
    Hello Stefano,

    The amount of current the VCC will draw depends on the Switch frequency. If you are switching at say 300kHz, the current draw will be approximately 2mA. The efficiency saving will be minimal, you are looking at ~ 50mW of saving...

    Calculations used.

    2mA*48V = 96mW
    2mA*24V = 48mW


    Hope this helps?

    David.
  • 0 in reply to David Baba
    Expert 2320 points
    Hi David,
    sure, it does not make sense to add an LDO for just 48 mW... when I will evaluate the power consumption of my design in details, I will keep in mind this information and choose what to do.

    Thanks,
    Stefano