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LP2996-N: DDR3

Yuta Nishie
Genius 4945 points
Part Number: LP2996-N
Other Parts Discussed in Thread: LP2996A

Tool/software:

Hi,

I am using LP2996-N as a regulator for DDR3, and it works without any problem so far.

However, when I look at the data sheet, it says LP2996A is for DDR3, not LP2996-N.

Could you tell me why LP2996-N is not for DDR3? Is it because the VDDQ (min) value is different?

Best Regards,

Nishie

  • +1
    TI__Mastermind 21855 points

    Hi Nishie,

    You are correct. DDR3 needs a 1.5V VDDQ and LP2996-N has a minimum VDDQ of 1.8V. LP2996A is recommended for DDR3 applications.

    Regards,

    James

  • 0 in reply to James Steenbock
    Genius 4945 points

    Hi James-san,

    Thank you for your reply.

    You said VDDQ requires 1.5V, but I have been able to use LP2996-N to run DDR3.

    Is it correct to understand that LP2996A is recommended, but LP2996-N can also be used?

    Best Regards,

    Nishie

  • 0 in reply to Yuta Nishie
    TI__Mastermind 21855 points

    Hi Nishie,

    When you say that you have used LP2996-N, do you mean that you can operate the part at 1.5V VDDQ or do you mean that DDR3 is working with a higher voltage?

    Regards,

    James

  • 0 in reply to James Steenbock
    Genius 4945 points

    Hi James-san,

    I checked with the customer. I apologize for my lack of confirmation.

    VDDQ is supplied from a different power supply IC.

    Therefore, is it correct to understand that LP2996N can be used?

    Best Regards,

    Nishie

  • 0 in reply to Yuta Nishie
    TI__Mastermind 21855 points

    Hi Nishie-san,

    The LP2996-N has a minimum VDDQ input of 1.8V but DDR3 requires 1.5V. Earlier you mentioned that the LP2996-N was still working for your DDR3 so I was wondering what voltage you are currently sending to the LP2996-N to make it work for DDR3?

    I can't recommend the LP2996-N since it does not meet the DDR3 needs theoretically but your initial statement suggests that the IC is operating below the stated minimum of the datasheet. Let me know if I am misunderstanding.

    Regards,

    James

  • 0 in reply to James Steenbock
    Genius 4945 points

    Hi James-san,

    The customer's method of supplying power to the DDR3 is as follows. Does my answer below answer your question?

    VDD=1.5 V (supplied from another power supply IC)
    VDDQ=1.5V (supplied from another power supply IC)
    VREFCA=0.75 V (supplied from LP2996 N)
    VREFDQ=0.75V (supplied from LP2996 N)
    VTT=0.75V (supplied from LP2996 N)

    Best Regards,

    Nishie

  • +1 in reply to Yuta Nishie
    TI__Mastermind 21855 points

    Hi Nishie-san,

    Understood, so the customer is supplying 1.5V to the LP2996-N VDDQ pin and is not seeing any issues with their testing or their system?

    That is strange considering the datasheet says LP2996-N has a 1.8V minimum VDDQ but I haven't done extensive testing on the device.

    The only reason for not using this part for DDR3 would be that the voltage range isn't sufficient but if the customer is already using this IC and there are no issues then I don't see a problem with it.

    Another interesting point is that on the LP2996-N product page, the minimum output is listed as 0.656V which would suggest that VDDQ can go as low as 1.35V.

    After seeing all this, I believe the LP2996-N should be fine for DDR3 and it sounds like the customer is already using it successfully. The ICs themselves are fairly simple so as long as the input voltage is working and the output current is sufficient (both version use 1.5A so this is fine), you shouldn't run into issues with the DDR3 application.

    Regards,

    James

  • +1 in reply to James Steenbock
    TI__Mastermind 21855 points

    Hi Nishie-san,

    One other thing I should point out is that your AVIN should be higher according to the highlighted datasheet sections below:

    If your VDD = AVIN, then VDD should be at least 2.2V.

    Regards,

    James