LM70840-Q1: Overheating to over 100 degrees C

Hi Alfredo, 

What is the switching frequency of the application? What is the thermal resistance of the PCB? Below is the quickstart calculator for this device.

https://dr-download.ti.com/design-tools-simulation/calculation-tool/MD-LuIrFjvWzJ/A0/LM70XX0_quickstart_calculator_A0.xlsm

Can you please fill out the spreadsheet? It will give us a better understanding of your application. Thanks,

Ben

Hi Alfredo,

I see that the switching frequency is 2.2MHz, which is the cause of the IC running hot. Is it possible to lower the switching frequency, like operating at 400kHz?

Ben

Attached is the filled out spreadsheet...

0830.LM70XX0_quickstart_calculator_A0.xlsm

I did try reducing the switching frequency to 450 kHz, but it only reduced the temperature to about 75 degrees C.

Ok so I just discovered that the inductor is actually getting hotter than the chip.  I reduced the switching frequency to 290 kHz and chip gets to about 70 deg C, the inductor gets to about 100 deg C.

Hi Alfredo,

In the LM70880-Q1 EVM user guide, figure 3-11 shows a thermal performance image that is similar to what you are seeing. The design specs are:

VIN=48V, VOUT=5V, Fsw=400kHz, IOUT=8A

Similarly, LM706A0-Q1 EVM user guide, figures 3-14 and 3-15 has the thermal performance images of:

It seems that the thermals for the IC is reasonable at 400kHz and room temp.

Ben