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Power Management IC suggestions Required (3.3V @ 6 amp, 2.5V @ 0.3 amp and 1.2 V @ 3 amp)

Kloon Janck
Prodigy 50 points
Other Parts Discussed in Thread: TPS54620, TPS75003

Hello Experts,

                 I need to ask a very simple question: I am designing a board with Spartan 3 FPGA (XC3S1000) with some interface ICS from MAX (422 and 232) and a USB micro controller. For FPGA I have designed its power circuit using TPS 75003. In this design the theoretically calculated current requirement for 3.3V (for full design) is about 6 AMP where as the output current of TPS is 3 AMP (current requirement for FPGA is 3 AMP) Please suggest any suitable power management IC for my design (having Spartan 3 FPGA and other interface IC). If I use a separate 3.3 Volt regulator (PTN series) for rest of my design and TPS 75003 for FPGA only I need to add a separate plane for it (one for VCCO and one 3.3V for rest of Interface Chip). Waiting for a quick reply or suggestion.

  • 0
    TI__Guru**** 151520 points

    At power.ti.com you can do a power quick search and find devices that meet your needs.  You didn't mention an input voltage, but the TPS54620 is an integrated 6A device that will likely work for you.  It has a PG, EN, and SS pin for easy sequencing, tracking, etc that is often required for processors.

  • 0 in reply to Chris Glaser
    TI__Expert 8890 points

    Kloon,

    Although Chris Glaser's solution is likely  the easier, more efficient solution, it is worth noting that external circuitry could be upgraded to afford 6Amp operation.  The easiest way to do this would be to, 1), find a FET replacement with similar gate capacitance and twice the current capability, 2) find a schottky diode that can support twice the current, and 3), upgrade the inductor to support the larger rms current (and saturation current).  Finding the FET replacement might be the most difficult and so I have attached an application note where an external, discrete, driver is added (that could drive virtually any reasonable gate capacitance) to the TPS75003 buck circuit to afford 5Amp operation.  You could use this application note to upgrade the circuit again to 6Amps. 

    6403.5-6Amp Buck upgrade slva164.pdf

    Bill

  • 0 in reply to Bill Stokes
    Prodigy 50 points

     

    Hello Bill,

            Thanks for your educative reply and the reference design. I am sorry but I am very immature in power circuit designing. And I know a good power design for digital design is highly crucial.

    So please help me in designing a good power solution for my digital design.

     

    Bill as per your recommendations I checked DIGIKEY site and found few replacements with my required current requirement: I have attached all the data sheets with the mail, please find some time to review my findings:

     

    In place of existing FET (existing: SI2323DS-T1-E3TR-ND) I would like to use FDC604PTR-ND.

     

    In place of existing schottky (existing: B320B-FDITR-ND) I would like to use 50WQ03FN-ND.

     

    In place of existing Inductor (existing: CDRH6D38-5R0) I would like to use 732-1074-2-ND.

     

    I need your expert opinion on my selected components for 3.3V @ 5.5 AMP.

    Please suggest me what else do I need to change like R1 (refer to the TPS 750003 example circuit).

     

    Waiting for your reply.

    Thanks again. 8424.FDC604PTR-ND.pdf5621.50WQ03FN-ND.pdf8507.732-1074-2-ND.pdf

  • 0 in reply to Kloon Janck
    TI__Guru**** 169546 points

    There is a design spreadsheet that can help you select components here: http://www.ti.com/litv/zip/sbvc002a.  The applicaiton note at http://focus.ti.com/lit/an/slva164/slva164.pdf is very similar to your design.  Your main concern is power dissipation in the FET and Schottky.  So I suggest using one of the tools to compute your maximum dissipation in each component and then choose a FET and diode that can handle the power dissipation.  The FET you choose cannot dissipate the power you need unless you plan to cool the FET with airflow.  The diode appears capable of handling the power dissipation .  When choosing an inductor, you want one with a saturation current 10-20% higher than your maximum output current to accomodate inductor current ripple and load transients.  So, I suggest finding one that has at least 6A saturation current.

  • 0 in reply to Jeff F
    Prodigy 50 points

     

    Thanks Jeff, the spreadsheet you provided is really very helpfull.

    I will get back to you after component selection. Thank you so much for your time and efforts.

    Bye

  • 0 in reply to Kloon Janck
    Prodigy 50 points

    Hello Jeff,

               With my immature experience i have selected the following components:

     

    Inductor = SRR1280-120MTR-ND
    FET = FDZ202P-ND
    schottky = 50WQ03FN-ND.

    Please review the components for my 3.3 V 5 AMP power design

    waiting for your reply. 3252.FDZ202P-ND.pdf

     8358.SRR1280-120MTR-ND.pdf

  • 0 in reply to Kloon Janck
    TI__Guru**** 169546 points

    The FET you selected can only handle 2W at 25C.  Your application will require it to dissipate about 1W.  What is your maximum ambient temperature?  You have to derate the FET package's power dissipation capability as the ambient temperature increases.  I doubt that the BGA package can handle 1W at high ambient temperatures.  I suggest a FET in a package with heat sink pad on the bottom that you solder to the board.  The inductor looks okay.

  • 0 in reply to Jeff F
    TI__Expert 8890 points

    Hi Kloon,

    I thought that I would give a few of my own comments, building on Jeff's discussion.  All the FETS that have been suggested so far have been very similar.  And, if they can be kept cool, then any of these solutions could work.  The data sheet for the FDZ202P is a good example where on the last page it shows a layout where there is a 1.5in x 1.5in square of 2oz copper to get an effective thermal resistance of 64degC/Watt - which would afford operation in your application to approx 86degC ambient.   The situation for all the fets discussed so far is approximately the same.  Many times, I have split the size of the copper thermal plane between the top and bottom layers (and sometimes I have used inner layers for cooling too) using 10 or more thermal vias, near the drain pins, to conduct heat - and this would probably be required in your application due to the fact that the copper that you use is likely 1oz or less.

    One other note, if your operating current is 5.5Amps, I would suggest finding an inductor with a saturation current of at least 20-30% higher rating and with a temperature rise at 5.5Arms of 20degC or less.

    Bill

  • 0 in reply to Jeff F
    Prodigy 50 points

    H6082.IRLMS4502TR-ND.pdfello Jeff,

             Thank you so much for your reply. Without your help I could not have come to this point.

    My ambient temperature will not increase above 50 degree centigrade. Jeff I searched another FET part number IRLMS4502TR-ND please review it as well, this FET can handle 1.1 W at 70 degree centigrade.

    I am waiting for your valuable suggestions.

    Thanks once again for your reply.

    Take Care 6011.IRLMS4502TR-ND.pdf