• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 82 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

TPS7A20U: TPS7A20U Thermal calculation

Murugavel S
Prodigy 115 points
Part Number: TPS7A20U

Tool/software:

Hi TI team,

We are in the process of freezing a design with a TPS7A20U regulator. We need your support with the thermal calculation to ensure that the IC does not exceed the Junction temperature maximum (Tjmax). We have done a calculation, which I have disclosed below. Can you please correct the calculation If I made any mistake in it?

Note: Kindly consider the PCBA designs are up to the mark and that all the design constraints are followed.

TPS7A20U
Vin(V) 5 E4
Vout(V) 3 E5
Iout(A) 0.1 E6
Iq(A) 0.01 E7
Pd(w) 0.21 E8
   
Tjmax(deg C) 125 E10
Ta(deg C) 25 E11
Rth 476.1905  Consider Tj =125, TA=25; (E10-E11)/E8 E13
Tj 140 Consider 40 degC ambient; (E8*E13)+40 E14

We have noticed that the maximum junction temperature in the datasheet is mentioned as 125degC. We want to know the TJ during TA= 50 degC, 60degC and 70degC

Regards,

Murugavel.S

  • 0
    TI__Expert 3805 points

    Hello Murugavel,

    The Junction-to-ambient thermal resistance of the TPS7A20U is 201.4 °C/W. The junction temperature can be calculated with equation 3 from the datasheet:

    TJ = TA + (RθJA × PD)

    Ambient Temperature (C)  Junction Temperature as per RθJA  (C)
    50 92.294
    60 102.294
    70 112.294

    Best Regards,

    Daniel

  • 0 in reply to Daniel Esparza
    Prodigy 115 points

    Hi Daniel,

    Thanks for your support. My concern is that the thermal resistance of the TPS7A20U is 201.4 °C/W.  I hope the value of the Rth is calculated for an ambient temperature of 25 °C. If the ambient temperature rises from 25degC to 50degC, whether the thermal resistance value change or not?

    Example:

    Rth= 125(Tj)-50(Ta) / 0.21W

    =357.14C/W

    Hence, Tj = 50+(357.14*0.21)

                 Tj   = 75degC

    Kindly confirm, is my understanding right or not?

    Regards,

    Murugavel.S

  • 0 in reply to Murugavel S
    TI__Expert 3805 points

    Hi Murugavel,

    The device will dissipate heat thru convection and thru the connection to the PCB. The Junction-to-ambient thermal resistance of the package is 201.4 °C/W, which is calculated based on die size, location of the heat source in the die, type of package, etc. Your calculation on Rth is not accounting for any thermal dissipation capabilities of the device, so I recommend the following application note and application report to expand on this topic:

    Semiconductor and IC Package Thermal Metrics (Rev. D)

    Using Thermal Calculation Tools for Analog Components (Rev. A)

    Best regards,

    Daniel