• State Resolved
  • Locked Locked
  • Replies 11 replies
  • Subscribers 64 subscribers
  • Views 5748 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS7A47: About current limit

Yuto Sakai
Mastermind 6100 points
Part Number: TPS7A47

Hi,

Q1,

According to P.7 of the datasheet, Minimum I(CL) is 1A, and Typical I(CL) is 1.26A.

But , According to Figure 10 on P.9 , I(CL) is more than 1.5A over recommended operating range.

Could you tell me which is correct I(CL)?

And I would like to know the maximum value of I(CL). Could you let me know the infomation?

Q2,

Could you let me know the method of overcurrent protection?

Is this foldback overcurrent protection?

Q3,

Could you tell me know the time "from overcurrent to detection" and "from the start of current limit operation until the output voltage reaches 0 V"?

Best Regards,

Yuto Sakai

  • 0
    TI__Mastermind 23361 points
    Hi Yuto,

    Q1, I did a bench measurement with the EVM for this part, I was seeing around 1.7A current limit at room temperature at 90% * 0.5V.
    Q2, it's not foldback current protection. Regardless of the voltage you apply on the Vout, the current limit stay roughly at 1.5 - 1.7A with one of the EVMs. For a foldback current LDO, the current limit is voltage dependent. We have a application note that provides more details explanations on constant current limit and foldback current limit. Please see it here: www.ti.com/.../snva558.pdf (page 13-17)
    Q3, overcurrent can cause thermal shutdown. In thermal limiting, the output voltage drops and the load current can be reduced to any value(including zero). No performance characteristic specifications apply when a part is operating in thermal shutdown mode. From past experience, the part could enter thermal shutdown mode within tens of micro seconds after it hits thermal temperature.

    Thanks,
    Jason Song
  • 0 in reply to Jason Song
    Mastermind 6100 points

    Hi Jason-san,

    Thank you for your kind reply.

    Q1,

    I think that the value of electrical characteristic (min 1A, typ 1.26 A) is due to variation, is it correct?

    Q2,

    I understand that the method of overcurrent protection looks like Figure 8 on p.12 of application notes,

    Is that really okay?

    Best Regards,

    Yuto Sakai

  • 0 in reply to Yuto Sakai
    TI__Mastermind 23361 points
    Hi Yuto-San,

    Q1, yes, you are right, we only used a small number of units to generated the char curves, so there could be some difference between the datasheet typical value and the values in the char curves.
    Q2, this chart shows a typical current limit profile. There is another application note that has more detailed explanations on this kind of current limit. Please see here: www.ti.com/.../snva736.pdf

    Regards,
    Jason Song
  • 0 in reply to Jason Song
    Mastermind 6100 points
    Hi Jason-san,

    Thank you for your kind reply.
    I will return to Q3,I would like to know the time from becoming overcurent condition to current limit detection.
    Please let me know the value if it has.
    I don't require guaranteed value, reference value is OK.

    Best Regards,
    Yuto Sakai
  • 0 in reply to Yuto Sakai
    TI__Mastermind 23361 points

    Hi Yuto-San, 

    Q3, the value is different for each different part, but roughly the time is tens of microseconds. 

    Regards, 
    Jason Song

  • 0 in reply to Jason Song
    Mastermind 6100 points
    Hi Jason-san,

    Thank you for your reply.
    I have additional queation.
    Could you tell me the maximum and minimum value of thermal shutdown temperature if it has.
    Reference value is OK, too.

    Best Regards,
    Yuto Sakai
  • 0 in reply to Yuto Sakai
    TI__Mastermind 23361 points

    Hi Yuto-San, 

    The temperature for the device to enter thermal shutdown is 170C; the recovery temperature is 150C. We actually listed the thermal shutdown numbers in our datasheet, please see its datasheet on Page 7. 

    Regards, 
    Jason Song

  • 0 in reply to Jason Song
    Mastermind 6100 points

    Hi Jason-san,

    Is it possible to teach how the temperature variation entering the thermal shutdown is?

    Also, could you tell me the max and min value of the temperature entering thermal shutdown?

    It's OK even if it is the reference value.

    Best Regards,

    Yuto Sakai

  • 0 in reply to Yuto Sakai
    TI__Mastermind 23361 points
    Hi Yuto-San,
    From my past experience, usually for the same device, the thermal shutdown does not vary that much from part to part(difference usually is smaller than +/-2C). We don't have min and max spec for thermal shutdown. If you only need a reference value, I would suggest you to use the typical number as your reference.

    Regards,
    Jason Song
  • 0 in reply to Jason Song
    Mastermind 6100 points

    Hi Jason-san,

    Is there a relational expression between "junction temperature (TJ) of the main pass-FET"(It is written on page 22 of the data sheet) and "Operating virtual junction temperature, TJ"(It is written on page 5 of the data sheet)?

    I think that "junction temperature (TJ) of the main pass-FET" is the same as "Operating virtual junction, TJ".

    However the absolute maximum rating of the junction temperature is 125°C(<170°C),

    If "junction temperature (TJ) of the main pass-FET" is the same as "Operating virtual junction, TJ",

    I think that it will be broken before it reaches 170°C.

    I would like to know if there is a relational expression between these two temperatures.

    Best Regards,

    Yuto Sakai

  • 0 in reply to Yuto Sakai
    TI__Mastermind 23361 points
    Hi Yuto-san,

    The Tj junction temperature discussed in "10.3 Thermal Protection" section is the temperature that the device would shutdown its own output when excessive heat is dissipated in the LDO such as a short circuit scenario. This is a protection mechanism that usually happen without a very short period of time that can help prevent permanent damage to the device . Thermal shutdown protection also allows device to recover when excessive heat condition has been removed or improved.

    The device may or may not work when junction temperature exceeds the absolute maximum ratings. The Tj junction temperature in the "6.1 Absolute Maximum Ratings" describes the maximum temperature of the junction at which the device is still operational within its specifications and without deteriorating device reliability. System level design should consider to let the part operate within its maximum rated temperature. Operating at Maximum Junction Temperature or higher may reduce device expected operational life time.

    Regards,
    Jason Song