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Original question:

LM5069 and LM5068, Hot-Swap-Problem

LM5068: LM5068 output capacitance

Mason Noh
Expert 2490 points
Part Number: LM5068
Other Parts Discussed in Thread: LM5067,

Hi TI,

I'm using hot swap controllers in my schematic.

The power supply is 32~60V at 20A, and output capacitance is 390µF. 

My problem is it can not start even 1A load because of OCP.

When I moved to output capacitor to infront of sensing resistor. It can start well at full load range.

Is it normal? I attached waveforms of CS pin.

#1 CH4: VSENSE (pin5)

#2 CH4: VSENSE (pin5)

Parameters

1.input voltage: 32~60V

2.Output current: 20Amax

3.Rs: 1.3mohm

Please let me know any side effect when I moved capacitors.

Thank you

  • 0
    TI__Guru** 104276 points

    Hi Noh,

    What is the type of load? If it is DC-DC load, suggest to use PWRGD to enable the load. This helps to reduce the stress on the FET during starting a load along with large capacitive load

    Best Regards,

    Rakesh

  • 0 in reply to Rakesh
    Expert 2490 points
    Thank you for your prompt reply.
    But I can't use enable function.
    Could you explain the change in OCP level depending on cap location? Does it have any side effect?
  • 0 in reply to Mason Noh
    TI__Guru** 104276 points
    Hi Noh,

    Thank you!
    For your system specs (20A load, 390uF cap), I suggest to use LM5067 device. It offers SOA protection for the hot-swap FET though power limit function (PWR).

    If you like to continue with LM5068, please send me below test waveforms for understanding. Test at max. input voltage of 60V
    1. Vin, Vout, Timer, input current (probe actual input current)
    2. Vout, GATE, Timer, input current (probe actual input current)

    Best Regards,
    Rakesh
  • 0 in reply to Rakesh
    TI__Guru** 104276 points
    Hi Noh,

    Did you able to get test waveforms ?

    Best Regards,
    Rakesh