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TPS51200: Query regarding REFIN/REFOUT pins

Kaitav Sapre
Prodigy 10 points
Part Number: TPS51200

Tool/software:

Hi,

I have a couple of quick question on TPS51200.

1. If I don’t want to use the REFOUT pin in my application, can I leave REFIN pin unused? If it is allowed to leave REFIN unused, how should it be connected (pulled down/up via resistor, directly connected to VLDOIN, etc.)?

2. If REFIN is used in the design via VLDOIN and voltage divider (0.6V for DDR4), but REFOUT is not used and just tied to a 0.1uF capacitor to GND, does it have any adverse effects? I know that it should be a problem functionally, but just in case there's anything else that I should be aware of.

Thanks,

Kaitav

  • 0
    TI__Mastermind 19310 points

    Hi Kaitav,

    1) VO follows REFOUT and REFOUT requires REFIN so you need to have the recommended external components for REFIN and REFOUT even if you don't plan to connect REFOUT to an external device.

    2) The TPS51200 doesn't have an issue with REFOUT being disconnected as long as it has a 0.1uF capacitor for regulation. However, usually DDR4 needs some sort of reference voltage so double check to see if you need REFOUT or not for your DDR4 system.

    Regards,

    James

  • 0 in reply to James Steenbock
    Prodigy 10 points

    Hi James,

    Thank you so much for the clarification.

    We are not using REFOUT pin in our application for DDR4 reference voltage (VREFCA) and using a discrete voltage divider instead. However, we do have REFOUT and REFIN connected as suggested in the datasheet with the required components, except that we are using 10nF for REFIN instead of 1nF, which I think is not a concern (especially based on reading some other threads), right?

    I want to clarify my understanding gap with "The output voltage, VO, is regulated to REFOUT." With no REFIN input (for example, pulled down), will there be no VO output?

    The functional block diagram and section 7.3.8 indicate that VO and REFOUT seem to be independent in terms of voltage generation. Please correct me I got it wrong. 

    Regards,

    Kaitav

  • +1 in reply to Kaitav Sapre
    TI__Mastermind 19310 points

    Hi Kaitav,

    The 10nF should be fine, I don't see an issue with that choice.

    REFIN feeds into a voltage follower (unity gain buffer) that is responsible for generating REFOUT. Without REFIN, there's no REFOUT voltage.

    Also, VO will not be enabled unless the REFINOK internal signal is active. This signal only activates if REFIN voltage is applied. REFINOK is one of the three inputs needed to activate VO (also called VTT for termination voltage).

    The VOSNS input comes directly from VO and is referenced against the REFOUT voltage. This internal system allows VO to follow the REFOUT voltage. 

    Regards,

    James

  • 0 in reply to James Steenbock
    Prodigy 10 points

    Hi James,

    Thank you so much for your detailed and helpful reply.

    "VO will not be enabled unless the REFINOK internal signal is active..." -> Perfect! Exactly what I was trying to clarify.

    I appreciate the other information as it helped me to understand/interpret the functional block diagram better.

    Thanks again.

    Regards,

    Kaitav