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TPS2413 based ORing application question

Kepcoate
Prodigy 140 points
Other Parts Discussed in Thread: TPS2413, TPS2412

Hi,

I have a high current ORing application. Where a set of each 3.3V,5V and 12V, PSUs are ORed and fed to backplane ( cPCI, VME etc) . The current on these PSU can range between 10A to 120A on 3.3V and 5V. For 12V, it is less than 10A. The question I have is:

1. To handle the power dissipation on FET without heatsink (only PCB pad) I want to use four FETS in parallel ( 8 for bidirectional blocking). Is TPS2413 designed to drive multiple FETs that require fast turn OFF?

2. Is there a way to use multiple TPS2413 in sync so that paralleled FETs can be controlled by individual device and high current handling setup be achieved?

Any other devices that can be used in this kind of application. It seems TPS2413 like devices are geared for board level use.

Thanks

  • 0
    TI__Genius 9415 points

    Is the 120A total or per channel or both?

    We regularly handle 4 FETS (2 back to back pairs). Eight is a lot of gate capacitance turn on and turn off  will be slower than the fast turn off specification for the part.

    I don't know your system requirements and wondered if we could use the 12volts with drivers to the gates of the 3V and 5V FET groups. the Gate output from the TPS2413 could switch the 12V drivers.

  • 0 in reply to Bob Kando
    Prodigy 140 points

    Bob,

    The requirement is 120A per channel.

    Do you have a specific driver in mind?

    Another thing I wanted to ask is, in this ORing topology when 4 FETs are in parallel, then in order to establish reverse voltage across the FETs on the PSU that is slightly lower, to turn off the TPS2413 gate drive, wouldn't it take 4X times more reverse current? Then the PSU that is of lower voltage will have to sink all that current. I am not sure how different Vendor PSUs will handle sink current. Any comments.

    Thanks for the reply.

     

  • 0 in reply to Kepcoate
    TI__Genius 9415 points

    I've attached a schematic of a driver for fast turn off that has been used in other applications. I don't have a proven high going drive circuit but I thought we may be able to switch the +12 V through to the gate of the power FETs with a small fet driven from the TPS241x gate.

    You're right about the higher reverse current through the lower impedance of the multiple FETs. It may be better fory ou to use the TPS2412 which does not need reverse current to turn off. There is more about the operation of these two controllers in the datasheet and there is an app note on the TPS241x product pages that describes the two control systems used in these parts.

    FET Driver.doc
  • 0 in reply to Bob Kando
    Prodigy 140 points

     

    Thanks Bob.

    The reason I was going for TPS2413 vs TPS2412 was these notes from datasheet. My application is the second one.

    "The TPS2412 is a better solution for a mid-rail bus that is re-regulated."

    "The TPS2413 is a better solution for low-voltage buses that are not re-regulated, and
    that may see large load steps transients."