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LM5116: Pre bias function

user4979999
Prodigy 690 points
Part Number: LM5116

Hi,

customer has question below, thanks.

1.      Can LM5116 buck solution support pre-bias startup?

example : LM5116 buck to 12.5V and Vout pre-bias 12V, can LM5116 work normal?

  • 0
    TI__Mastermind 25590 points

    Lynn,

    Yes, check section 7.4.1 of the datasheet.

    "During this initial charging of CSS to the internal reference voltage, the LM5116 will force diode emulation. ..... Forcing diode emulation during soft-start allows the LM5116 to start up into a pre-biased output without unnecessarily discharging the output capacitor"

    You may also need to adjust your UVLO resistors. Your circuit will allow current to flow through the body diode of the high-side FET (unless you add something to block it). That means with VOUT=12V pre-bias, your VIN may see up to 12V through that body diode. If you set your UVLO to turn on above 12V, you should not have an issue.

    -Sam

  • 0 in reply to Samuel Jaffe
    Prodigy 10 points
    Hi Sam,
    Thanks for reply, Can I just make sure the LM5116 VIN voltage is higher than VOUT 12V pre-bias, and it will no current to flow through the body diode of the high-side FET? my application LM5116 VIN should be 48V.

    And one more question, when VOUT=12V pre-bias, and VIN is 48V, LM5116 Vout setup to 12.5V, then to enable LM5116 and set the soft-start time very fast( <100us),my think it should like ZVS switch, will LM5116 still have a large inrush current when enable? anything need to be cared for this application?
  • 0 in reply to Aaron Shih
    TI__Mastermind 25590 points
    Aaron,

    Yes, if VIN>VOUT, you will have no current through the body diode of the high-side FET. This is fine.

    If VOUT = 12V, then the IC turns on and regulates to 12.5V, there should not be a very large inrush current. But if the current is too large, add a cap on SS.

    -Sam