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LM5161-Q1: Device Operation after Fast Ramp of VIN

Shinichi Yokota
Genius 9715 points
Part Number: LM5161-Q1
Other Parts Discussed in Thread: LM5161

Hello,

Can a Fly-Buck converter with LM5161-Q1 start up successfully with a VIN of fast ramp of about 100 V per 20 to 30 µs? Some tests suggest the LM5161-Q1 draws a high rush current with a peak of about 1 A.

Best regards,
Shinichi Yokota

  • 0
    TI__Mastermind 23815 points

    Hi Shinichi,

    I think the amount of rush current is also related to how much capacitor that at the input of the device.

    I think it is recommended to try the fast slew rate on the Evaluation module of the LM5161. 

    Thanks

    -Arief

  • 0 in reply to Arief Hernadi
    TI__Genius 9715 points

    Arief,

    How fast of ramp rate was the design of LM5161-Q1 originally targeted for VIN? What was the fastest ramp rate of VIN under which LM5161-Q1 has ever been tested?

    Best regards,
    Shinichi Yokota

  • 0 in reply to Shinichi Yokota
    TI__Mastermind 28980 points

    We design and test for the harshest line transients. Validation testing includes many line transient test that different sectors (including automotive) most conform to.

    I recommend to observe the response of the power design on the EVM to see if it can conform to application specifications.

  • 0 in reply to Marshall_Beck
    TI__Genius 9715 points

    Marshall,

    Is it correct to understand that specific numbers for VIN's rise time are not available? I'm afraid I didn't ask for a general comment which recommends, "I try by myself." I just wanted to confirm what was seen in a circuit with LM5161-Q1.

    Best regards,
    Shinichi Yokota

  • 0 in reply to Shinichi Yokota
    TI__Mastermind 28980 points

    The LM5161 can handle the fastest of line transients, the fastest being a hot-plug, where the RC delay will dictate the slew rate of the transient.

    The COT architecture is very tolerant of line transients.

  • 0 in reply to Marshall_Beck
    TI__Genius 9715 points

    Marshall,

    Again, is a specific number on VIN's ramp rate available? Otherwise, I cannot verify the behavior I've seen in a LM5161-Q1 circuit. I already provided the VIN ramp rate I've observed in the circuit as approximately 100 V per 20 to 30 µs at the start of this thread. I just wanted to know whether the LM5161-Q1 circuit will start up successfully with this fast VIN ramp. If you insist, "I must try an EVM by myself," let's stop this discussion and I'm afraid I'll leave this thread "Unsolved."

    Best regards,
    Shinichi Yokota

  • 0 in reply to Shinichi Yokota
    TI__Mastermind 28980 points

    The inrush current will be dictated by the input loop, including the inductance in that loop. If you have large input cap and small inductance in the loop, the inrush current will be large to charge up the input cap. 

    You have a faster slew rate on the input, the inrush will be larger.

    Is the inrush current disrupting part performance? I need to understand the issue with the part before sharing details on how we validate our parts.