LM5116: Device is hot

Danilo A.

Part Number: LM5116

Hi Team,

Our customer is using LM5116 in their application but the device is hot even if the output voltage is correct. According to our customer,

I have a problem with signal form Pin LO and HO of LM5116, high side and low side MOSFET.

The yellow is LO (signal Low side) mosfet and purple is HO (High side) mosfet

Output voltage is 12V very good but IC LM5116 is so hot and buzzing sound from the inductor

I have 4 buck regulators from LM5116. 2 for 5V and 2 for 12V from 20-50V input

Attached are the schematic diagram, waveform and gerber files.

He als added,

I think the problem is in the signal on the gate G of mosfet. it's not square pulse. Can I solve this by reducing the switching frequency? Or do something to reduce the settling time of the signal.

When i connect pin 11 (DEMB) of LM5116 with resistor 10K to GND, signal in FET is square, but the IC LM5116 gets hotter when i connect it directly to ground.

Regards,

Danilo

over 2 years ago

0 EricLee over 2 years ago

TI__Guru 51881 points

Hello Danilo

Would you please let me know the IC temperature and test conditions ?

The IC temperature is always higher than your expectation ? if not, please let me know the condition when the temperature increases.

Would you please share inductor current waveform when you hear the buzzing sound? and please let me know the test conditions.

- Eric Lee

0 Danilo A. over 2 years ago in reply to EricLee

TI__Mastermind 27030 points

Hi Eric,

Please see the response of our customer.

In case Pin DEMB connect directly to GND, I used buck 5V for load 0.7 - 1 A output. IC temperature is about 70 C degree but MOSFET is not hot. I think this is not normal because other buck isn't hot with the same condition.

With inductor current waveform, I can't determine but I can record the video for you

Regards,

Danilo

0 EricLee over 2 years ago in reply to Danilo A.

TI__Guru 51881 points

Hello Danilo

Can you replace the IC ? Usually, the device temperature is high when the device switches fast at the heavy load. If it is hot when switching slowly or at the light load, there is a possibility your device might be damaged.

- Eric Lee

0 Danilo A. over 2 years ago in reply to EricLee

TI__Mastermind 27030 points

Hi Eric,

According to our customer,

I changed to another IC but this still happens. Do you have any ideas on how to fix the buzzing sound from the inductor?

He shared this video.

6038.IMG_0302 low resolution.zip

Regards,

Danilo

0 EricLee over 2 years ago in reply to Danilo A.

TI__Guru 51881 points

Hello Danilo

I suggested replacing the IC in order to check a damage is making the device hot or not.

Can you test it again after changing R10 to 3.9k and C17 to 15nF ? .

-Eric Lee

0 Danilo A. over 2 years ago in reply to EricLee

TI__Mastermind 27030 points

Hi Eric,

According to our customer, he replaced the IC but the problem still remains. He also added that when he replaced the R10 and C17, he no longer hear the buzzing on the inductor.

He would like to know if he can use the values of R10 and C17 for a 5V output. He noticed that when the input is 18V and the outputs are 12V and 5V without load, the current consumption is 0.08A. Is this normal?

Regards,

Danilo

0 EricLee over 2 years ago in reply to Danilo A.

TI__Guru 51881 points

Hello Danilo

It is good to hear that the issue is resolved by changing R10 and C17. Please download the Quick Start https://www.ti.com/lit/zip/snvu051 and send me four completed Quick Start (One per one rail.) for my review.

The current consumption can be ~0.08A. It is possible since the LM5116 is not designed for low-IQ applications.

- Eric Lee

0 Danilo A. over 2 years ago in reply to EricLee

TI__Mastermind 27030 points

Hi Eric,

According to our customer, he can't remember the MOSFET specification so that he can't complete the Quick Start.

Regards,

Danilo

0 EricLee over 2 years ago in reply to Danilo A.

TI__Guru 51881 points

Hello Danilo

MOSFET parameters are not important when checking the loop compensation design .

- Eric Lee

0 Danilo A. over 2 years ago in reply to EricLee

TI__Mastermind 27030 points

Hi Eric,

Please see the accomplished Quick Start from our customer.

6404.LM5116_quickstart.xls

Regards,

Danilo

0 EricLee over 2 years ago in reply to Danilo A.

TI__Guru 51881 points

Hello Danilo

I think the user inputs in the Quick Start doesn't match with what you told me. Almost all inputs are different. I guess you sent me a wrong file.

For example, Input range is 15-25V in the QS. Rs is 10mOhm in the schematic, but it is 53mOhm in QS.....

- Eric Lee

0 Danilo A. over 2 years ago in reply to EricLee

TI__Mastermind 27030 points

Hi Eric,

Our customer resend this file.

7140.LM5116_quickstart (2).xls

Regards,

Danilo

0 EricLee over 2 years ago in reply to Danilo A.

TI__Guru 51881 points

Hello Danilo

Inductor value in the QS doesn't match with what you told me. It can be close to 10uH by increasing the Ripple Current % to ~ 70%
The feedback resistor values are different than the schematic.
Please input de-rated output capacitor values which are typically 20-50% less than the rated capacitance values

- Eric Lee

0 Danilo A. over 2 years ago in reply to EricLee

TI__Mastermind 27030 points

Hi Eric,

According to our customer,

"Please input de-rated output capacitor values which are typically 20-50% less than the rated capacitance values". I don't understand this sentence slightly.
This is the fixed Quick Start.

LM5116_quickstart (3).xls

Regards,

Danilo

+1 EricLee over 2 years ago in reply to Danilo A.

TI__Guru 51881 points

Hello Danilo

The capacitance of the ceramic capacitor is reduced by applying a bias voltage. You have to input the practical/de-rated output capacitance values in the C24 and C25 cells.

I used 50% de-rated capacitance values and reduced Fc to 12.5kHz

Then, the recommended Rcomp becomes 7.8kΩ, Ccomp becomes ~ 16nF

Would you please try 7.8kΩ and 16nF combination and check if any improvement ?

- Eric Lee

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LM5116: Device is hot