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LP2998: LP2998

Mohamed Yashar
Prodigy 40 points
Part Number: LP2998
Other Parts Discussed in Thread: LM2831

Hi, 

We have used LP2998MR for DDR3 termination whose inputs are 1.5V for PVIN and VDDQ, 3.3V for AVIN. Could you please review the attached schematics? Also, I need to know what is required input current for AVIN and PVIN, VDDQ. Please let me know your comments.

Thanks,

Yashar

  • +1
    TI__Mastermind 18185 points

    Hi Yashar,

    The schematic looks good to me. It looks like 47uF is sometimes recommended on PVIN when PVIN and AVIN are supplied separately but I don't see anything in the datasheet the says you can't use a 22uF. The main goal is to prevent your input voltage from dropping during a worst case transient load at VTT.

    The LP2998MR is designed to support +/- 3A transient loads so you need to make sure that your PVIN supply can handle the loading conditions you are expecting.

    VDDQ input impedance is typically 100k so if your VDDQ voltage is 1.5V you can expect a typical current of 15uA on this pin.

    For AVIN I'm not sure what the max current could be but 10mA would likely be more than enough as an estimate. There's really nothing in the datasheet to suggest you need more than 10mA capability. Since this device can work even without input capacitance, I can't imagine the AVIN current input being very high. 10mA may even be an overestimate.

    Regards,

    James

  • 0 in reply to James Steenbock
    Prodigy 40 points

    Thank you for your comments,

    Also, can you please review the below schematics?

    I have used LM2831 regulator for powering DDR3 and VTT VREF termination regulator LP2998 and For LM2831 given input is 3.3V and required output is 1.5V@400mA, I have given enable EN to other regulator's output side for sequence power on. Kindly provide your feedback on this and 22uf in Vin is sufficient for the input capacitance and Input current required for LM2831?

    Regards,

    Yashar

  • 0 in reply to Mohamed Yashar
    TI__Mastermind 18185 points

    Hi Yashar,

    Please create a separate post for this device review so that it goes to the correct team.

    Regards,

    James