LM5066I: LM5066I for 1.2k& 3.3kw application design review

Ryan Lee TW

Other Parts Discussed in Thread: LM5066I, CSD18536KTT

Hi Experts,

My customer wants to use LM5066I to design only for power switch, no need to use hotswap function.
As below layout screenshot, there are 6 MOSFETs, in light blue box in the middle...

Q1.

Can MOS be placed a little apart?
Customers think the advantage of dispersion is that there is a larger space for Via and copper paving, and it also increases the heat dissipation area. Is it right?
In other hand, when MOS gates turns on/off, will there be a time differences for the 6 switches while the MOS are placed a little apart?

Q2.
In 3.3kw design caculators, the column of Rds on must be filled in the value of a single unit(6.4 ohm) or 6 units in parallel(0.8 ohm)?
Because this column will affect the performance of temperature rise.

Q3.
Will the current design of Upper UVLO affect the start-up voltage?
Current Vin is 24V

Thanks.

LM5066I_Design_Calculator_REV_C_3.3kW.XLSX

over 2 years ago

0 Avishek Pal over 2 years ago

TI__Mastermind 30915 points

Hi Ryan,

Thanks for reaching out to us. We will get back to you by tomorrow end of the day.

0 Avishek Pal over 2 years ago in reply to Avishek Pal

TI__Mastermind 30915 points

Hi Ryan,

What does "no need to use hot swap function" mean? What are the functionalities required by the customer?

Please see the responses in the order of your queries.

1) MOSFETs can be placed a little apart. According to the datasheet of SQM120N10-3m8, RthJA is 40 °C/W with a 1" square of PCB area. Therefore, a 1" square of PCB area should be allocated for each MOSFET. This will help to improve the thermal performance as rightly pointed out by the customer.
There will not be any delay as such during turn on or off with this above MOSFET placement.

2) On resistance for a single MOSFET should be entered. However, the RDSON of SQM120N10-3m8 looks very high. It may not be suitable for this high current design. CSD18536KTT may be a viable option here. Please see the attached design calculator and let us know if there is any query. Kindly note here that as this is a high current design, a few design considerations need to be taken care of. Please share the schematic for our review.

LM5066I_Design_Calculator_3.3kW_Edited by TI.XLSX

0 Ryan Lee TW over 2 years ago in reply to Avishek Pal

Intellectual 616 points

Hi Avishek,

Thanks for your MOSFET suggestion, it has been promoted to him.

My customer think that only use LM5066I for power switch, so will not face the high current usage situation caused by hotswap.

The ambient temperature of the circuit is 25~50 degrees Celsius.

He was wondering if would face the situation of "Target Power Limit" up to 120W or not, due to the "FET Power dissapation at full load (per FET)" is 3.4W only.

In addition, what is the definition of "Maximum FET Junction Temperature" and "Target Power Limit".

Thanks for your kindly help.