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TPS51916 V5IN current and maximum DDR3 LDO support

Dan Andersen
Genius 11460 points
Other Parts Discussed in Thread: TPS51916

We are looking to use the TPS51916 in a 3.3V-1.5V (plus VTT) DDR3 application.  It will be supporting 2 banks of 72 bit DDR3 (9 devices).

First:  It appears the V5VIN current is always <1mA regardless of load or temp.  Since we do not have a 5V rail available (and want to minimize cost/size), can this be supplied from a reference voltage (say 12V->5V reference or zener)?

Second:  Is the 2A limit on the LDO VTT supply enough to support 2 banks? 

Thanks!

  • 0
    TI__Guru**** 191445 points

    It looks like those V5VIN specs are all for no load.  The internal circuits should not demand much current variation over load, but I'm not sure about the MOSFET drivers.  I bet they will draw more current under load.  The specs are based on how the device is tested at AT, which is probably no load and open loop.

    What is the current requirement for 2 banks?  You will have to answer that.  It will depend on the requirements for the actual DDR that you use.

  • 0 in reply to JohnTucker
    TI__Genius 11460 points

    We've calculated +/-1.5A on the DDR - which this appears able to handle.

    I was afraid of that on the V5VIN.  Any way we can get some current numbers on this over load?  We've got to figure out what we'll need to supply this....

  • 0 in reply to Dan Andersen
    TI__Guru**** 191445 points

    I don't directly support that device.  I usually monitor posts on DCAP2 control devices, as that control topology is one of my areas of expertise.  I'll see what I can find out, but you may have to wait for someone else to comment.

  • 0 in reply to JohnTucker
    TI__Mastermind 49450 points

    Hi Dan,

    John is right. The current on V5IN pin is for no load in the datasheet. The actually current based on the EVM is around 15mA in 12Vin, 1.5V/20A. Please review attached test report. You also can see the load regulation for VTT at +/-2A in attached report.

    Thanks,

    Nancy

    7776.TPS51916EVM-746Efficiency.xls