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WEBENCH® Tools/LM5175: 19 LM5175PWPR 12V-30V to 28.00V @ 15A

Orfeo Milani
Prodigy 20 points
Part Number: LM5175
Other Parts Discussed in Thread: LM5157

Tool/software: WEBENCH® Design Tools

Dear Sirs


Use LM5175 in the following project:

I enclose schematic and pcb in pdf format

VIN range 12-30V Vout 28V 15A 100Khz with a parallel of two inductor wurth 7443641000 10uH 37A 2.4 mOhm equivalent inductor 5uH 74A 1.2 mOhm.

With 13.5 V in input and 28 V in output the card works in buck-boost instead of working only in boost mode.


I think the main problem is that we developed it on 4-layer FR4, therefore the mosfet dissipation area does not allow to have short gate tracks.


One thing I checked between redoing the same project with the "LM5175 Buck-Boost Quickstart Tool - r9.xlsm" and with the "WBdesign" I get different results.


For example the compensation components (COMP pin) with the "WBdesign" I get 10Kohm + 15nF // 330pF with the "Buck-Boost Quickstart Tool - r9.xlsm"


I get 3K16 Kohm + 12nF // 39pF (NB by entering data of the inductance 5uH 1,2mOhm).


Another mistake we made is that of not having drawn tracks SW1 // HDRV1 and SW2 // HDRV2 side by side.


I would appreciate you to report any corrections before producing the next sample.

Best Regards

Orfeo MilaniSchematic Power.pdfPCB layout.pdf

  • 0
    TI__Guru* 76785 points

    Hi,

    We will reply tomorrow.

    Thanks,

    Youhao Xi, Applications Engineering

  • 0 in reply to Youhao Xi
    Prodigy 20 points

    Hi Youhao Xi


    I modified the circuit like the new diagram attached because with the oscilloscope I detected a cross-conducting problem between Q32 // Q33 and Q35 // Q36 that damaged the LM5175 chip.


    I replaced the LM5157 chip and I inserted R = 10 Ohm and a schottky diode to increase the dead times.


    I'm testing the Boost CCM mode circuit so I disabled Q30, Q31, Q34.


    The circuit is working with Vin = 13.5 V and Vout = 29V @ 15A.


    Are the changes I have made possible or can they cause problems?


    Is there any better solution?

    Thanks,

    Orfeo MilaniSchematic Power revB.pdf

  • 0 in reply to Orfeo Milani
    TI__Guru* 76785 points

    Hi Orfeo,

    Thank you for the updating.  What you did is the right way to create a dead time: slowing down the turn-on by the resistor, and speeding up the turn off throuth the diode.

    To make sure no more shoot-through would occur again, please monitor the high side and low side FET's Vgs and see there at least 20ns~30ns dead time between the two FET, measured at the FET's Vth level.  Please avoid excessive dead time.

    We do recommend to add 1 Ohm or so gate resistor before the FET is paralleled.  So in this case, you should have the following configuration:

                                         1 Ohm --> Gate1 

    DRV -->  (D//R)  -->  <

                                        1 Ohm --> Gate2

    The "<" sign above means split into two lines, one to each 1Ohm to gate;  "-->" is the signal flow direction.  (Sorry the Webench does not allow me to draw in the window).

    Thanks,

    Youhao