LM5175: Excessive temperature

Lao Hu

Intellectual 790 points

Part Number: LM5175
Other Parts Discussed in Thread: PMP10594

Hello,

The device is getting around 62°C and the inductor filter around 72°C, under no load with 12V input.

The results can be reproduced with various boards, regardless of the regulator's load (tested with no load).

I was checking similar situations:

A user changed the output capacitors to solved the issue (https://e2e.ti.com/support/power_management/non-isolated_dcdc/f/196/t/656330?LM5175-LM5175-Unstable-operation-high-current-draw-and-excessive-temperature). We already have 3 low ESR ceramic capacitors (22uF C3216X5R1V226M160AC) and two electrolytic (100uF EEE-FK1H101P, 220uF EEE-FK1H221P).
Vijay86929 (from TI) mentioned that an IC temperature could be in 10-15 degrees of ambient at no load. Cannot find the difference with LM5175 EVMs.
The board (from TI) seem to have low temperature (PMP10594 REV A) according with test results [http://www.ti.com/lit/ug/tidudy4/tidudy4.pdf].

Any idea what may causes this situation?

Attached additional info (schematic, SW1 & SW2 signals, thermal image).

Thanks

Lao Hu

over 7 years ago

0 Lao Hu over 7 years ago

Intellectual 790 points

Update:

When the input is 24V, the temperature increase to 72°C in the device and 98°C in the inductor filter.

0 Youhao Xi over 7 years ago in reply to Lao Hu

TI__Guru* 78645 points

Hi Lao,

It seems you set the circuit in CCM, and CCM will have circulating current even at no load. Your inductor looks like a small one. Please follow the quick start calculator to select the proper inductor to lower the power dissipation and temperature rise.

Thanks,
Youhao

0 Lao Hu over 7 years ago in reply to Youhao Xi

Intellectual 790 points

Hello Youhao Xi ,
Thanks for your feedback. Appreciated.
We changed the circuit to operate in DCM mode and the temperature was reduced to almost ambient. We expect to keep this mode in our application.
At the same PCB we have a second DC/DC with 24V output. We applied DCM mode and the temperature decrease, however not like the other converter. I will created another post regarding this situation.
Thanks
Lao Hu

Power management

Power management forum

LM5175: Excessive temperature