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Webench no longer recommending ceramic caps?

Matt Church
Prodigy 20 points
Other Parts Discussed in Thread: TPS54360, TPS54329E

Hello,

I have already used the TI Webench Designer for a number of DC/DC voltage converter designs and have been generally pleased with the results.  A few days ago I used the application again to see what it suggested for getting slightly more current out of a buck regulator design it had suggested before.  To my surprise, the smallest footprint it could come up with was nearly twice as large.  I got the same results even when I put in the original parameters I had used for the first design.  It seems that the difference is that it is now only recommending electrolytic and tantalum caps and not MLCCs as it has done in the past.  Does anyone know why this has changed?  I understand that MLCCs have their issues, but they can still be significantly over specified and still be smaller than what is being recommended.  Is there something newly discovered about MLCCs that I don't know that made TI change their mind as to their suitability? 

Any advice would be much appreciated.

  • 0
    TI__Expert 3085 points

    Matt,

    To reproduce your problem we would like to know more: Could you tell us which device you are designing with and what are your design specs?

    Thanks

  • 0 in reply to Surinder Singh
    Prodigy 20 points

    Sure, no problem.  Thanks for you help.

    I used the following specs with Webench:

    VinMin = 34.0V
    VinMax = 46.0V
    Vout = 30.0V
    Iout = 1.1A

    When I use those specs today, I get a footprint of 380 mm^2 and it suggests electrolytic caps, but when I used webench in November of last year, it generated the following design: (I'm sorry if it's hard to read, but I can't seem to attach the pdf it generated for me)

    Device = TPS54360DDA
    Topology = Buck
    Created = 11/30/12 9:19:42 PM
    BOM Cost = $4.46
    Total Pd = 2.04 W
    Footprint = 234.0 mm2
    BOM Count = 12

    1. Cboot MuRata GRM155R71A104KA01D
    Series= X7R
    1 $0.01 Cap= 100.0 nF
    VDC= 10.0 V
    IRMS= 0.0 A
    0402 8mm2
    2. Ccomp MuRata GRM033R60J103KA01D
    Series= X5R
    1 $0.10 Cap= 10.0 nF
    VDC= 6.3 V
    IRMS= 0.0 A
    0201 6mm2
    3. Ccomp2 Kemet C0603C470J5GACTU
    Series= C0G/NP0
    1 $0.01 Cap= 47.0 pF
    VDC= 50.0 V
    IRMS= 0.0 A
    0603 10mm2
    4. Cin MuRata GRM32ER72A225KA35L
    Series= X7R
    1 $0.38 Cap= 2.2 µF
    ESR= 7.0 mOhm
    VDC= 100.0 V
    IRMS= 4.4 A
    1210 23mm2
    5. Cout MuRata GRM32ER72A225KA35L
    Series= X7R
    1 $0.38 Cap= 2.2 µF
    ESR= 7.0 mOhm
    VDC= 100.0 V
    IRMS= 4.4 A
    1210 23mm2
    6. D1 Diodes Inc. DFLS1100-7 1 $0.19 VF@Io= 770.0 mV
    VRRM= 100.0 V PowerDI123 22mm2
    7. L1 Coilcraft XAL5050-223MEB 1 $0.83 L= 22.0 µH
    DCR= 100.0 mOhm
    XAL5050 54mm2
    8. Rcomp Vishay-Dale CRCW04024K75FKED
    Series= CRCW..e3
    1 $0.01 Res= 4.75 kOhm
    Power= 63.0 mW
    Tolerance= 1.0%
    0402 8mm2
    9. Rfbb Vishay-Dale CRCW040210K2FKED
    Series= CRCW..e3
    1 $0.01 Res= 10.2 kOhm
    Power= 63.0 mW
    Tolerance= 1.0%
    0402 8mm2
    10. Rfbt Vishay-Dale CRCW0402374KFKED
    Series= CRCW..e3
    1 $0.01 Res= 374.0 kOhm
    Power= 63.0 mW
    Tolerance= 1.0%
    0402 8mm2
    11. Rt Vishay-Dale CRCW040268K1FKED
    Series= CRCW..e3
    1 $0.01 Res= 68.1 kOhm
    Power= 63.0 mW
    Tolerance= 1.0%
    0402 8mm2
    WEBENCH
    ®
    Design
    Copyright © 2012, Texas Instruments Incorporated 2 ti.com/webench
    WEBENCH
    ®
    Design Report TPS54360DDA : TPS54360DDA 34.0V-46.0V to 30.0V @ 1.1A November 30, 2012 21:20:17 GMT-8
    # Name Manufacturer Part Number Quantity Price Properties Footprint
    12. U1 Texas Instruments TPS54360DDA 1 $2.52 Switcher
    R-PDSO-G8 57mm2

  • 0 in reply to Matt Church
    TI__Intellectual 2510 points

    Hello Matt,

    Thank you for your interest in Texas Instruments' power management solutions and for bringing this issue to our attention.

    As a work around in the mean time, you can click "Select Alternate Part" for Cout and next, select  "Create Custom Part". Here you can add cumulative specs for the ceramic cap and quantity.

    We will provide a solution as soon as possible.

    Regards,

    Flora

    Flora

  • 0 in reply to Flora Carreto
    TI__Intellectual 2510 points

    Hello Matt,

    The revised TPS54360 WEBENCH model is already available on line.

    Best Regards,

  • 0
    Prodigy 60 points

    Not sure where to post this, but...

    I've done a webench desigh using TPS54329E 6.0-16.0Vin, 5.0Vout 0.7A.

    Webench lists 22uF ceramics for Cin & Cout.

    Do these values take into account dc-bias?

    Rick Barnich

  • 0 in reply to Rick Barnich
    TI__Intellectual 2510 points

    Hi Rich,

    Voltage derating is taken into account for Cout.

    Best Regards,

    Flora