TPS92641: Tj calculation

K.Shidara

Expert 3225 points

Part Number: TPS92641

Hi team,

Would you advise that Tj calc below is correct?

In case of Iin=50mA, Vin=50V, Ta=25 deg

Tj = Ta + (RθJA(effective) x Power )

= Ta + Rθja x (Vin - Vcc) x Iin

= 25 + 38.7 x (50 - 8.5) x 50m

= 105.3 deg

Thanks

Best regards,

Shidara

over 6 years ago

0 Tuan Tran74 over 6 years ago

TI__Mastermind 18890 points

Hello,

Where are you getting Iin from? Is it the current into the TPS92641 or is it the current into everything including power stage?

Thanks Tuan

0 user5989296 over 6 years ago in reply to Tuan Tran74

Prodigy 50 points

Hi Tuan-san

It is the current of the VIN pin of the TPS92641.

Best regards,

Komiya

0 K.Shidara over 6 years ago in reply to user5989296

TI__Expert 3225 points

Komiya-san

Thank you so much for the information.

Tuan-san

Komiya-san is my customer who is asking.

Please advise about the Tj calculation inquiry on this.

Thanks

Best regards,

Shidara

0 Tuan Tran74 over 6 years ago in reply to K.Shidara

TI__Mastermind 18890 points

Komiya-san,

Your equation is a first approximation of the temperature. Please see the following report for this.

http://www.ti.com/lit/an/spra953c/spra953c.pdf

The junction temperature also depends your layout and components that are around the TPS92641.

Thanks Tuan

0 user5989296 over 6 years ago in reply to Tuan Tran74

Prodigy 50 points

Hi Tuan-san

Thank you for reply.

I have a more question.

What is the heat factor of the TPS92641?

Where should I reduce the loss to reduce the temperature?

Best regards,

Komiya

0 Tuan Tran74 over 6 years ago in reply to user5989296

TI__Mastermind 18890 points

Hi Komiya,

The heat dissipation on the TPS92641 comes from Vin and Iin of the part. If you reduce Vin or Iin you will accomplish that. Are you using VCC to run any other circuit in your design beside the switching FET's? The main current into the TPS92641 is used to drive the external switching FET's so by reducing the switching frequency or Gate charge of the FET's you will accomplish this.

Thanks Tuan

0 user5989296 over 6 years ago in reply to Tuan Tran74

Prodigy 50 points

Hi Tuan-san

Thank you for your reply.
No other circiut connect for the Vcc pin.
I will change the following conditions and confirm the heat.
FETs gate capacitance:33nC→10.6nC
Switching frequency:500kHz→300kHz

Best regards

Komiya

0 Tuan Tran74 over 6 years ago in reply to user5989296

TI__Mastermind 18890 points

Hi Komiya,

We have not heard back from you so we believe you have solved the issue. The thread will close now but will reopen if you reply.

Thanks Tuan

0 user5989296 over 6 years ago in reply to Tuan Tran74

Prodigy 50 points

Hi Tuan-san

Unfortunately the problem has not been resolved.

The temperature of the IC could be lowered to 120 degrees.

However, the specification is below 95 degrees.

Please let me know if there is any other way to lower the temperature.

Best regards

Komiya

0 Tuan Tran74 over 6 years ago in reply to user5989296

TI__Mastermind 18890 points

Hi Komiya,

Is temperature measured on the part or are you using math? If you are using math then I suggest you measure the temperature on the part.

Thanks Tuan

0 user5989296 over 6 years ago in reply to Tuan Tran74

Prodigy 50 points

Hi Tuan-san

I measured the temperature on the part.

The temperature of IC was 120 degrees.

Best regards

Komiya

0 Shashank Kulkarni over 6 years ago in reply to Tuan Tran74

TI__Expert 3640 points

Hello Komiya-san,

Do you require further help on this? If so, can you please provide the information Tuan asked for so that we can proceed?

If you do not need help, please let us know so that we can close the thread.

Thanks

Sumeet

0 Tuan Tran74 over 6 years ago in reply to Shashank Kulkarni

TI__Mastermind 18890 points

Hi Komiya-san,

The only way to reduce the temperature is better heat-sinking of the part, reduce the voltage on the part or the power FET gate charge.

Thanks Tuan

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TPS92641: Tj calculation