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LM25148-Q1: Power Dissipation Calculation

Muwei Zheng

Intellectual 1020 points

Part Number: LM25148-Q1
Other Parts Discussed in Thread: LM5148

Hi team,

Our customer is using attached quickstart calculator to calculate the power dissipation of LM25148-Q1. From the calculator Efficiency is calculated as 89.1% and total Pd is calculated as 6.2W. However the sum of Pd of each part is calculated as 5.27W below, which does not match the 6.2W result.

HSD : 1.7W
LSD : 1.4W
Inductor : 0.8W
IC : 1.11W
Current sense Resistor : 0.46W (=2mohm * 15.19A^2)
SUM=5.47W

Could you help check if the calculation is correct and what is the reason for the difference?

Condition:

- HSD : Infineon IAUC60N04S6L039

- LSD : Infineon IAUC100N04S6N022

- Inductor : Panasonic ETQP5MR68YLC

- Output Voltage : 3.3V

- Output Current 15.19A

LM5148-LM25148 Quickstart Calculator_rev3forPCI.zip

Thank you,

Muwei Zheng

over 1 year ago

0 Orlando Murray over 1 year ago

TI__Mastermind 22299 points

Hi Muwei,

That attachment is protected. what is the password?

I can look at the efficiency calculation details.

Did they measure 6.2W on the board?

Not there are some losses that are not accounted for in the quickstart calculator, like input inductor DCR, PCB copper losses, and other PCB parasitics.

-Orlando

0 Muwei Zheng over 1 year ago in reply to Orlando Murray

TI__Intellectual 1020 points

Hi Orlando,

Sorry I have attached the calculator result below with no password.

6.2W is coming from the calculator as customer don't have a board right now.

Pout = 3.3V * 15.19A = 50.1W

Pin = 50.1W / 89.1%(from calculator) = 56.3W

Pd = 56.3W - 50.1W = 6.2W

0 Orlando Murray over 1 year ago in reply to Muwei Zheng

TI__Mastermind 22299 points

Hi Muwei,

That second attachment is not working, can you try to reattach or email me

-Orlando

0 Muwei Zheng over 1 year ago in reply to Orlando Murray

TI__Intellectual 1020 points

Hi Orlando,

Please find if this attachment works. Apologize for the wrong attachment.

LM5148-LM25148 Quickstart Calculator_rev3forPCI.xlsm

0 Orlando Murray over 1 year ago in reply to Muwei Zheng

TI__Mastermind 22299 points

Hi Muwei,

There are some deadtime losses that are approximately 0.715W at full load.

They should be dissipated on the LS FET because of the body diode.

We didnt include it in the losses because it could potentially be dissipated by an external diode.

Hope this helps,

-Orlando

0 Muwei Zheng over 1 year ago in reply to Orlando Murray

TI__Intellectual 1020 points

Hi Orlando,

Thank you for your reply.

Orlando Murray said:
We didnt include it in the losses because it could potentially be dissipated by an external diode.

Does this "external diode" refer to the body diode of LS FET?

Should customer include the 0.715W deadtime loss to calculate the efficiency?

0 Orlando Murray over 1 year ago in reply to Muwei Zheng

TI__Mastermind 22299 points

Hi Muwei,

Yes use the 0.715W dead time losses for efficiency.

There is an option for an external Schottky on row 93-95.

-Orlando