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LP2998-Q1: upper and lower VDDQ tolerance

Ross Parlour
Intellectual 1260 points
Part Number: LP2998-Q1
Other Parts Discussed in Thread: LP2998, TPS51200-Q1

Hi,

My customer is doing an analysis on our LP2998-Q1 DDR memory termination and came across an interesting case.

Their question is regarding the LP2998-Q1 DDR Termination Regulator and it’s upper and lower VDDQ voltage tolerances. They are are planning to use the device with a VDDQ nominal of 1.35V and AVIN and PVIN voltages at 3.3V for DDR3L memory MT41K128M16JT-125. The datasheet says, "The device also supports DDR3 and DDR3L VTT bus termination with VDDQ min of 1.35V".  This could be interpreted to mean that 1.35V is a minimum rating and the device may not work within a tolerance.  It almost sounds like 1.35V VDDQ is right near the bottom end of the device capability (never a good place to operate a device). Yet on Figure 5 from the same datasheet, one can see a stable voltage even as low as 1V, so you can probably see our confusion on the matter. I also noticed two other points that might turn out to be an issue.

I can summarize 3 questions both my customer and I now have:

  • When using the LP2998-Q1 for DDR3L with VDDQ nominal of 1.35V, what are the upper and lower VDDQ voltage tolerances the LP2998 supports?  For example, is a VDDQ voltage tolerance of 1.283V to 1.45V acceptable (this is what the DDR3L memory chip lists as the VDDQ range)?

 

  • I noticed for the input supplies in the datasheet it’s stated, “It is recommended to connect PVIN to voltage rails equal to or less than 3.3 V to prevent the thermal limit from tripping because of excessive internal power dissipation”. Are they operating “at the edge” of the device capability here?

 

  • Another small concern is the fact that looking at the revisions of the datasheet it looks like the DDR3 functionality was added at a later stage, which means the device was not originally planned to work with DDR3. Is this the case? Is the part safe to use with DD3L memory that my customer has selected? Is there a better solution, that again has an extended operating temperature range (say -40C to +95C)? I had never noticed this previously, but after some investigation, I want to be sure.

Regards,
Ross

  • 0
    TI__Mastermind 24075 points
    HI Ross,

    1. 1.35V is the typical VDDQ voltage for DDR3L application. LP2998-Q1 should work with VDDQ tolerance of 1.283V to 1.45V.

    2. LP2998-Q1 is a linear regulator. The power loss is (PVIN-VTT)*Ivtt. The recommendation of connecting PVIN to less than 3.3V is from a thermal concern, not electrical concern. The operating ragne of PVIN is up to 5.5V. This spec is available on datasheet section 7.4.

    3. The part was released in 2007. At that time DDR3L was not available yet. Later on we did qualification for DDR3L application and add related information on datasheet. It is fine to use this part for DDR3L application.

    TPS51200-Q1 is another option for DDR3L appliction. This part is being used by many autombile customers.

    Thanks
    Qian
  • 0 in reply to Qian Chen
    TI__Intellectual 1260 points
    Hi Qian,

    Thank you for your prompt response to this. I have just one final question regarding the VDDQ voltage. What is the minimum VDDQ rating for DDR3L application? Since a tolerance of 1.283V won’t work for my customer, if they take into account the voltage drop.

    Regards,
    Ross