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Original question:

AM5718: AM571x DDR memory map of Linux SDK.

TPS51116: Revision History of TPS51116

SY Yoon
Genius 3381 points
Part Number: TPS51116

Hi, 

My customer has been using the TPS51116 for a long time.

It recently found a changes point in datasheet.

In the application schematic, The resistor value connected to the CS pin has changed.

Can I know reason why it changed?

Best regards.

  • 0
    TI__Expert 5965 points

    Hi SY,

    In the 2018 datasheet, a sensing resistor was used instead of Rdson sensing which was used in 2009 datasheet, that's why the CS resistance is different. 

    Regards,

    Weidong

  • 0 in reply to Weidong Zhu
    Genius 3381 points

    Hi,

    Why was a sensing resistor used instead of Rdson sensing?

    My customer designed schematic by referring to the application schematic in the 2009 datasheet. 

    It made 10 custom boards and there is no output voltage from two boards.

    When the resistor value changed from 5.1K to 7.15K, it worked normally.

    Below waveform is the TPS51116 output. yellow is output and green is input. 

    The red is the abnormal output.

    Best regards,

  • 0 in reply to SY Yoon
    TI__Expert 5965 points

    Hi SY,

    Can you provide customer schematic and also show how S3/S5 are controller? From the above waveform it looks like the rail powers up whenever VIN is going up. Also why VIN is going down when there is issue?

    The 2018 datasheet was updated to a new format, which we need to provide a complete design example. In this case, the TPS51116 EVM design example was used, in which resistor sense was used. 

    In any case, Rdson sense should still be working if it's configured correctly.

    Regards,

    Weidong

  • 0 in reply to Weidong Zhu
    Genius 3381 points

    Hi, 

    The previous waveform was created to show that the Vout output is strange.

    Vout output does not work occasionally when 5Kohm is connected to CS pin.

    If only the CS input resistance is replaced from 5.11K to 7.15K, it works normally.

    This phenomenon occurs more often at low temperatures than at room temperature.

    The inserted waveform measured only the Vout waveform.

    Normal 

    Abnormal

    DC-DC supports both Resistor sense and Rdson Sense. Is there a way to know which mode is operating in either mode?

    Have you ever had a case like this?

    My client is reluctant to open the schematic to E2E, but wants a review.

    Could you review schematic?

    Best regards

  • 0 in reply to SY Yoon
    TI__Expert 5965 points

    Hi SY,

    The resistor on CS pin sets the current limit. So from the waveform you are showing, it looks like sometimes the current is limited and Vout can not reach to the desired value. There could be several reasons:

    1. Rdson variation. Since Rdson sensing is use, and usually Rdson has wide tolerance between part to part, it's not surprising that some board is not showing current while other boards are. Of course it depends on the load current. What is the max load current in this application and which MOSFET they are using?

    2. Current limit threshold variation between part to part. From the datasheet you can see that the OCL voltage has some tolerance as well, and can vary between part to part. 

    I'll send you a friend request so you can send me your email address and we can review the schematic.

    Regards,

    Weidong