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LM5069: LM5069

Stuart Linzer
Intellectual 260 points
Part Number: LM5069

Hi Power Group,  

Working with LM5069 in our three channel 28V power supply.  

When the 28V output turns on, load draws 45 amps for 300usecs.  

Nominal output current is 5amps with the output limit set at 6Amps (Rsenss = 0.009 ohms). 

What I would like to do is increase the Circuit Breaker response time to 1mS.  

My thought is to add an RC circuit to the sense pin (resistor in series with Sense pin and capacitor from Sense to Vin).  

Please let me know your thoughts on doing this.  

Regards, 

Stuart

  • 0
    TI__Guru* 89026 points

    Hi Stuart,

    Thanks for reaching out!

    I understood that you would like to add RC on the Rsense to allow 45A for 300usec but it also causes delay in turning OFF the MOSFET for short-circuit event, which is risk for the MOSFET

    Is 45A the inrush current from the load ? we can manage/ limit the inrush current by controlling the slew-rate of GATE of LM5069. Please refer 3.2.2.7 Choosing the VOUT Slew Rate in https://www.ti.com/lit/an/slva673a/slva673a.pdf

    Best Regards,

    Rakesh

  • 0 in reply to Rakesh
    Intellectual 260 points

    Hi Rakesh,  

    My load is an LED light fixtures which is digitally controlled.  The inrush event happens about 10ms after power is applied.  Vout slew rate control is not an ideal solution as the load has under-voltage monitoring an doesn't turn on until a 20V threshold is crossed. .  It seems the inrush looks more like a high current event rather than inrush.  +28V is stable for about 10ms after which the LED load wakes up and the high current pulse is presented.

    We made some changes on the load side and current pulse is now 15A for 300uS.  Nominal current is 5A so short current detection hits at about 10A.  

    My goal is to delay short circuit response so the circuit beaker acts more like a slow blow rather than a fast blow.  

    Regards, 

    Stuart

  • 0 in reply to Stuart Linzer
    TI__Guru* 89026 points

    Hi Stuart,

    Understood. As I mentioned earlier, it is risk for the FET to delay the short circuit response. You may able to design with stronger SOA FET like psmn4r8-100bse. 

    The other option is to design 10A solution so that the circuit breaker threshold will be 10A*1.9 = 19A

    Best Regards,

    Rakesh