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TPS65051-Q1 minimum on time

Toshio Ushikubo
Mastermind 9620 points
Other Parts Discussed in Thread: TPS65051-Q1

Hello,

 

Customer plan to use TPS65051-Q1 and has following question.

 

Please advise the minimum on-time of DCDC1 and DCDC2.

Customer wants to confirm if their design has margin for minimum on-time.

 

Best Regards.

  • 0
    TI__Genius 16030 points
    Hello Ushikubo-san,

    We don't have any data on minimum on time since it's not a datasheet spec for this device. But TPS65051-Q1 supports 100% duty cycle mode, so even with low input voltages, it will continue to regulate the output voltage until the input voltage drops below the dropout. The minimum input voltage can be calculated by equation 3 in the datasheet.

    Regards,
    Karl
  • 0 in reply to Karl Wallinger
    Mastermind 9620 points

    Hello Karl-san,

     

    Thank you for your answer.

     

    I understand that it isn’t datasheet spec.

    But customer wants to know the minimum on time margin for their VINDCDC1/2, VOUT use case.

    So could you supply any evaluation data of minimum on time?

    Or how did TI validated the minimum on time margin for worst use case of datasheet spec (VINDCDC1/2=6V max and VOUT=0.6V min) when this device was developed?

    (Rough estimation of worst case on time is “0.6V/6V x 1/2.25MHz = 44ns”, and TI should have checked the device margin against 44ns on time.)

     

    Best Regards.

  • 0 in reply to Toshio Ushikubo
    TI__Genius 16030 points
    Hello Ushikubo-san,

    I now realize that I answered about minimum OFF time instead of minimum ON time. I apologize for the confusion.

    The device was tested at 6Vin / 0.6V out and will work, though I don't know what sort of margin analysis was done beyond that condition. However, I just tested DCDC1 and DCDC2 on an EVM at 6.5Vin / 0.6Vout and the device still regulated to 0.6V out with 38ns on time (Fsw for this device was 2.4MHz). So there is some margin to 6Vin / 0.6V out case.

    If your customer is using a higher output voltage than 0.6V, then that is additional margin beyond this case.

    Regards,
    Karl
  • 0 in reply to Karl Wallinger
    Mastermind 9620 points

    Hello Karl-san,

    Thank you for your answer.

    I want to confirm if following my understanding is correct.

    It is guaranteed that TPS65051-Q1 work correctly with Vin=6V, Vout=0.6V and following load condition.

      DCDC1:1A

      DCDC2:0.6A

    Best Regards.

  • 0 in reply to Toshio Ushikubo
    TI__Genius 16030 points
    Hello Ushikubo-san,

    Because minimum on-time is not a datasheet parameter, I cannot say that it's guaranteed. I do know that we tested units at Vin=6V, Vout=0.6V, and that I tested one EVM at Vin=6.5V and Vout=0.6V, so I have some confidence that it will work.

    Please let me look through all our characterization data, and I will let you know if I find more information.

    Regards,
    Karl
  • 0 in reply to Karl Wallinger
    TI__Genius 16030 points
    Ushikubo-san,

    What is the actual Vin/Vout condition the customer will be using?

    Regards,
    Karl
  • 0 in reply to Karl Wallinger
    Mastermind 9620 points
    Hello Karl-san,

    Customer will use following condition.
    Vin:5V
    Vout: 1.35V and 1.8V

    Best Regards.
  • 0 in reply to Toshio Ushikubo
    Mastermind 9620 points

    Hello Karl-san,

    Please answer following new question from customer.
    Please advise TI recommended value of “△IL / Maximum Current(DCDC1:1A and DCDC2:0.6A)” for example 20% to 40% for TPS65051-Q1.

    Customer wants to know this value to determine optimum inductance vale for their use case.



    Also please let me known the situation of looking through all your characterization data (minimum on time).

    Best Regards.

  • 0 in reply to Toshio Ushikubo
    TI__Genius 16030 points
    Hello Ushikubo-san,

    We don't have any char data on minimum on time for this device. Based on the customer condition of 5V in / 1.35V out @ 2.475MHz worst case, on time would need to be 109ns. In my opinion, there is sufficient margin from the < 38ns that I measured. However since it's not guaranteed in the datasheet, the customer should validate this themselves.

    Regarding max current, we specify up to 1A and 0.6A DC, so this should be the maximum continuous current. It's common to target 15% to 20% less for design margin to account for load steps, and variance from theoretical max current to actual max current.
    Note that the minimum current limit is 1.19A and 0.85A respectively, so peak current should not exceed these values.

    Regards,
    Karl