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Inverting Buck Boost toporogy of 300W

Ryuji
Guru 20090 points
Other Parts Discussed in Thread: LM25119, LM5119, LM5088

Hello,

Our customer request the following specification inverging buck-boost.
Could you please let me know the recommend DCDC and FET for the following requirement?
---------------
Vin:12V
Vout : -10.5V
Iout: 30A
---------------
I found the PMP8928 which is 65W inverging buck-boost reference design as maximum output power in PowerLab. 
> http://www.ti.com/tool/PMP8928
If we can't achieve above requirement , please let me know the problem.( inductor or diode ?)

 


Also I simulated these requirement by Power Stage designer.
As a result, we need the inductor about 0.5uH/63A. I think that this value is




Best Regards,
Ryuji Asaka

  • 0
    TI__Intellectual 1435 points

    Ryuji,

    I would consider a 2-phase buck controller for 30A output (15A per phase).  LM25119 reference designs are a good place to start.   See the link below for a 20A design that could be stretched to 30A with adjustments to current sense resistor, inductors and possilby the FETs.

       http://www.ti.com/tool/pmp7428

  • 0 in reply to David Pace
    TI__Guru 58941 points

    Hi Ryuji

    One of LM5119 reference design can deliver 30A. Please refer the schematic at http://www.ti.com/tool/pmp7990. 

    Regards,

  • 0 in reply to EricLee
    Guru 20090 points
    Hello,

    Thank you for the reply.
    I understood that the reference design which have maximum output power.
    I refer these schematics.

    Also I have another question about LM5088 in webench.
    I think that LM5088 can output maximum power for inverting buck-boost toporogy in Webench.
    LM5088 webench setting is the following.
    Vin range : 4.5V ~ 75V
    Vout range : -65V ~ 0V
    Iout/Isw : 10A

    I simulated with Vin:12V, Vout:-10.5V, Iout:10A.
    Then LM5088 is not listed with the comment of " Can't find any suitable couple FET/Diode for the Design".

     <Qusetion 1>
    Could you please let me know the reason of  "Iout/Isw:10A" ?
    Since LM5088 is DCDC controller, we can use this device with more current depending on Power Staage.

    <Question 2>  
    Could you please let me know the reason of " Can't find any suitable couple FET/Diode for the Design" ?
    According to Power Stage Designer , FET / Diode current is the following. (ripple current is 25%)

    FET: Max Current 21.75A, RMS current : 13.47A
    Diode : Max Current 21.75A, RMS current :  13.94A ,Diode Losses 7W
    I think that there are the FET/Diode for above current. Are there any concerning without current , powe rlosses?

    Best Regards,
    Ryuji Asaka
  • 0 in reply to Ryuji
    TI__Intellectual 1435 points

    Hello Ryuji,

     <Qusetion 1>

    Could you please let me know the reason of  "Iout/Isw:10A" ?
    Since LM5088 is DCDC controller, we can use this device with more current depending on Power Stage.

    The 10A limitation is somewhat arbitrary and based on two considerations:

    a) strength of gate drivers -  Higher current requires larger FET and more gate drive current.  Higher than 10A current  is possible  if a low  gate charge FET is selected or if discrete emitter follower transistors are added between driver and FET gate to boost gate current

    b) non-synchronous bucks are seldom used above 10A because of the power dissipation in the free-wheeling diode.  Synchronous controllers are preferred to reduce the heat generated by the rectifier.

    <Question 2>  
    Could you please let me know the reason of " Can't find any suitable couple FET/Diode for the Design" ?
    According to Power Stage Designer , FET / Diode current is the following. (ripple current is 25%)

    The Webench library of discrete elements is limited.  It does not link to all available discrete components.  If you have a power stage that works at 10A in the buck configuration, the same power stage will work in the inverting buck-boost configuration.