I designed a DC-DC power supply, it is a buck-boost topology, the design is based on DC-DC controller LM5118, the circuit is as below picture shows:
When I am debugging the circuits, I found the output voltage level is right as expected voltage 48V under different current load, but the inductor of L16 is very hot even with a current load 1A, is there anyone can give some clues what caused the inductor hot issue and how to fix this issue?
Thanks and with best regards
Calvin

 

What is the inductor saturated current rating?

 

Your inductor may be physically too small so it is saturating as @crutschow is asking.
Is the inductor the recommended value?
Also, is the core material designed for the frequency the switcher is running at?

 

What is the inductor saturated current rating?

I attached inductor datasheet for your reference, would you have a look?
Thanks

 

Your inductor may be physically too small so it is saturating as @crutschow is asking.
Is the inductor the recommended value?
Also, is the core material designed for the frequency the switcher is running at?

Yes, the inductor was recommended by TI design tools, I attached datasheet for your reference, would you like to have a check if it is right?
Thanks

 

Did you measure the inductor’s temperature?

It is specified to operate at 125 C. That is pretty hot. Maybe you don’t have a problem.

No temperature meter? When my friends and I were teen-agers when referring to transistor case temperatures (all the cases were metal then) we used to say that if it was not hot enough to fry spit it was ok, so all you really need is a wet finger.

 

I found the output voltage level is right as expected voltage 48V

What is the input voltage?

 

The input voltage range is from DC 35V-55V

 

Did you measure the inductor’s temperature?

It is specified to operate at 125 C. That is pretty hot. Maybe you don’t have a problem.

No temperature meter? When my friends and I were teen-angers when referring to transistor case temperatures (all the cases were metal then) we used to say that if it was not hot enough to fry spit it was ok, so all you really need is a wet finger.

Yes, maybe you are right, I didn't do a temperature measurement, I just put my finger on the inductor surface and I feel it is very hot, I should do temperature measurement to see if it goes beyond 125 degree C.
Thanks for your reminding, it likes a thunder hit me

 

Hello

What is the actual value of L16?
The datasheet shows 220 uH, the schematic shows 47 uH.

Bertus

 

Hello

What is the actual value of L16?
The datasheet shows 220 uH, the schematic shows 47 uH.

Bertus

I attached a wrong datasheet at the beginning, the value is 47uH, the right datasheet is available now.

 

I attached a wrong datasheet at the beginning, the value is 47uH, the right datasheet is available now.

Available where?

 

Available where?

Here it is! can you see it? I already attached the datasheet in previous reply actually.
Thanks!

 

Yes, maybe you are right, I didn't do a temperature measurement, I just put my finger on the inductor surface and I feel it is very hot, I should do temperature measurement to see if it goes beyond 125 degree C.
Thanks for your reminding, it likes a thunder hit me

The temperature of the inductor surface is 81 degree c at room temperature 20 degree C, the highest working temperature of inductor is 125 degree C, I am sure if it has enough margin, because the board supposed to work at 50 degree C room temperature, we may need verify this by putting in temperature chamber but setting the environment temperature of 50 degree C.
Thanks
Calvin

 

The temperature of the inductor surface is 81 degree c at room temperature 20 degree C, the highest working temperature of inductor is 125 degree C, I am sure if it has enough margin, because the board supposed to work at 50 degree C room temperature, we may need verify this by putting in temperature chamber but setting the environment temperature of 50 degree C.
Thanks
Calvin

Did you measure the inductor’s temperature?

It is specified to operate at 125 C. That is pretty hot. Maybe you don’t have a problem.

No temperature meter? When my friends and I were teen-agers when referring to transistor case temperatures (all the cases were metal then) we used to say that if it was not hot enough to fry spit it was ok, so all you really need is a wet finger.

The temperature of 81 degree C I measured was done by a fluke IR image scanner, it maybe not very accurate.

 

Have you looked at what the inductor current really is? I think it is above 1A!

 

Have you looked at what the inductor current really is? I think it is above 1A!

Inductor current is not a stable value during charging and discharging, 1A is the DC-DC current load

 

Inductor current is not a stable value during charging and discharging, 1A is the DC-DC current load

Yes and the P-P current might be 3A while the DC is only 1A.

 

still less than the 4 amp rating of the inductor

 

Do you have a scope? Look at the voltage across R353/354. With a scope not a meter. I want to see the waveform.