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TPS2491: Inquiry about formula(3)

Shinichi Inoue
Guru 21721 points
Part Number: TPS2491

Dear Specialists,

My customer is considering TPS2491 and has a inquiry about formula(3) of datasheet P.12.

I would grateful if you could advise.

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According to equation(3) of the datasheet,

Inquiry(1)

I cannot understand this formula

I think

Ts(max)/RθJC(max) < PLIM and Tj(max)/RθJC(max) > PLIM

transform the formula

Ts(max)/RθJC(max)<Tj(max)/RθJC(max)

PLIM : 0<(Tj(max)-Ts(max))/RθJC(max)

This is not correspond to formula(3), it seems to be typo.

Could you please let me know.

Inquiry(2)

TJ(max) is a junction temperature.

On the other hand, Ts(max) is a case temperature.

I think case temperature is not the same as junction temperature.

Could you please let me know why Ts(max) is used?

---

I appreciate your great help.

Best regards,

Shinichi

  • 0
    TI__Guru** 105811 points

    Hi Shinichi,

    I will look into this and get back tomorrow.

    BR,

    Rakesh

  • 0 in reply to Rakesh
    TI__Guru** 105811 points

    Hi Shinichi,

    TJ(max) is the junction temperature of the MOSFET

    Ts(max) or Tc(max) is the case temperature of the MOSFET

    As shown in the below simplified MOSFET thermal model, the PFET (=PLIM in this case) flows through the loop in steady state condition.

    For a given power stress across the FET (PLIM), the temperature rise above the case node can be calculated as follows.

    Temperature rise = TJ(max) - Ts(max)  = PLIM * RθJC(max)

    so PLIM = [ TJ(max) - Ts(max) ]  /  RθJC(max)

    BR, Rakesh

  • 0 in reply to Rakesh
    Guru 21721 points

    Hi Rakesh,

    Thank you for your reply.

    I understand the formula(3).

    I'll share your suggerstion with the customer.

    I appreciate your great help.

    Best regards,

    Shinichi