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TPS61088: TPS61088 Theta JA/JC question

Redick Lee
Prodigy 570 points
Part Number: TPS61088
Other Parts Discussed in Thread: TPS55340, TPS61175, BQ40Z50-R1

Hi Team,

 

Sorry to bother you.

As we can see from below table, may I know why the data of theta_JA is lower than theta_JC?

Per our understanding, most of theta_JA data is higher than theta_JC. Thanks for your help and time.

 Yours Faithfully

Redick Lee

  • 0
    TI__Mastermind 40080 points

    Hi Redick,

    Very good question, we'll consult the related expert for the detailed information. Please wait in patience.

  • 0
    TI__Mastermind 40080 points

    Hi Redick,

    For the parts which have big thermal pad at the bottom side, like TPS61088, the Theta Ja is lower than Theta Jc. Because the heat can be directly dissipated through the bottom side thermal pad, which means the thermal is mainly handled by the bottom side thermal pad.

    You can check the datasheet of some other IC, like TPS61175 or TPS55340, they have no thermal pad at the bottom side, therefore the heat could only mainly be dissipated though the pins.  For those ICs, the Theta Ja is > Theta Jc.

  • 0 in reply to Helen chen
    Prodigy 50 points

    For the parts which have big thermal pad at the bottom side?

    Assume chipset power=1W , Tj=100’c

    From spec thermal information, and Tc=Tj-(P*Rjc) , Ta=Tj-(P*Rja), Tb=Tj-(P*Rjb)

    Tj=100’c

     Tc=100-(1*39.8)=60.2

     Ta=100-(1*38.8)=61.2

     Tb=100-(1*15.5)=84.5

    Show as below….

    I don’t understand, why Ta can higher than Tc

  • 0 in reply to Helen chen
    Prodigy 50 points
    For the parts which have big thermal pad at the bottom side?
    Assume chipset power=1W , Tj=100’c
    From spec thermal information, and Tc=Tj-(P*Rjc) , Ta=Tj-(P*Rja), Tb=Tj-(P*Rjb)
    Tj=100’c
     Tc=100-(1*39.8)=60.2
     Ta=100-(1*38.8)=61.2
     Tb=100-(1*15.5)=84.5
    Show as below….
    I don’t understand, why Ta can higher than Tc
  • 0 in reply to Jesse Liu
    TI__Mastermind 40080 points

    Hi Jesse,

    From your calculated data, you can see that the board temperature is very high, 84.5C, therefore the air temperature near the board can be a number below 84.5C. so 61.2C is reasonable value.  For the IC's with big thermal pad, the heat is hard to be dissipated from the top side, so it is reasonable that the Ta >Tc

  • 0 in reply to Helen chen
    Intellectual 285 points

    Hi,

     two questions ask:

    1. About OperationStatus register ,from the BQ40Z50-r1 Technical Reference,i knwon that,it has two way to access,one is used   0x54 register  ,another way is ManufacturerBlockAccess() or ManufacturerData(),

         These two way can read the same results?

    2.How to read ManufacturerAccess() 0x0054 OperationStatus register? is the same as below? First write command 0x00,data sent 0x0054,then read command 0x23?

    Thanks!

  • 0 in reply to Helen chen
    Prodigy 50 points

    Hi Helen

    If follow your spec.Please refer to attached. 

    Rja=Rjc+Rca right??  this is why I can't undrerstand Ta can highrt than Tc

    Thanks!

    B/R

    Jesse 

  • 0 in reply to Jesse Liu
    TI__Mastermind 40080 points

    Hi Jesse,

    Your model only fit for the ICs which mainly dissipate thermal through the pins and the top case. For the ICs with big thermal pad at the bottom side, this model doesn't fit,  which means Rja≠Rjc+Rca . I'll attach the model picture if I could find it.

  • 0 in reply to Helen chen
    Prodigy 50 points
    Rja≠Rjc+Rca ??
    Please help to provide model picture.
    Heat source is inside the chipset. right?
    I think even "with big thermal pad at the bottom side"
    Tc value should bigger than Ta.
  • 0 in reply to Jesse Liu
    TI__Mastermind 40080 points
    There's a special team develop the model. But be sure the data on the datasheet is right. I didn't get the model from that team yet. And need some time. Please discuss this off line. Thanks!