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LM5001: The soft start time of LM5001

takahiko yokota
Mastermind 7135 points
Part Number: LM5001

Hi


I think the soft start time of LM5001 calculate using comp sink current.
Could you tell me the formula to calculate soft start time?
Best regards,
Yokota
  • 0
    TI__Intellectual 1010 points
    Hello Yokota,

    An internal COMP pull-up resistor (typical 5k) supplies the charging current to the soft-start capacitor at the COMP pin. The charge current is about (5V-1.3V)/5k when Vout starts to ramp up. It is not easy to calculate the soft start time because this soft-start control scheme only makes the COMP voltage increase gradually. The total soft start time is not only related to the SS cap and charging current but also related to the output capacitor and load current during startup. I would recommend using an EVM to measure the soft start time per your application condition.

    thanks

    Gavin
  • 0 in reply to Gavin Jin
    Mastermind 7135 points

    Hello Gavin-san

    Thank you for the reply.
    I tried to measure the soft start time using EVM.
    But I couldn't set up Tss=4ms under Vin=12V, Vout=51V and Iout=100mA.
    Can LM5001 set up 4ms on specification?

    Best regards,
    Yokota

  • 0 in reply to takahiko yokota
    TI__Intellectual 2645 points
    Hi Yokota
    You can try to change soft-start capacitor to change SS time. increase C to increase SS time. (you can take the Figure 17 in datasheet as reference).