LM25118: temperature for surrouding parts of LM25118

lee peng kiat

Intellectual 450 points

Part Number: LM25118

Dear Sir/Madam,

I used LM25118 in my design which output = 12V, 1.6A and Input =10V to14V.

During operating condition, I found that the 2 Diode tmeperature is about 92 degree C,

2 MOSFET is about 82 degree C and 10uH Choke Coil is about 76 degree C.

Part used for MOSFET : Vds = 60V, Id = 61A, Rds = 11.3m ohm.

Part used for Diode : VR = 40V, IF = 5A

Part used for Coil : Rated Current = 7.5A, Rdc = 12.4m ohm.

Pls help to see whether I am using the surrounding parts which is lower in spec for this application.

Thanks.

over 7 years ago

0 Youhao Xi over 7 years ago

TI__Guru* 78370 points

Hi Lee Peng Kiat,

Thank you for using the LM25118. The thermal issues may be caused inadequate cooling and also by improper package of the device received. Regarding the diodes, they should be Schottky diodes or ultra fast switching diodes. A regular diode may have much more losses owing to the slow reverse recovery.
Regarding the MOSFETs, the Qg may be high, leading to higher switching losses. For your application, you don;t need 60V FET. 20V FETs will have adequate voltage rating, and Qg can be much smaller than the 60V FETs.

Thanks,
Youhao Xi

0 lee peng kiat over 7 years ago in reply to Youhao Xi

Intellectual 450 points

Hi YouHao Xi,

Both Diodes in my application are Schottky dodes.

But diodes temperature is 92 degree C.

Both Diodes : Vds = 40V, Id =4A

Is it due to the current rating ?

Thanks.

0 Youhao Xi over 7 years ago in reply to lee peng kiat

TI__Guru* 78370 points

Hi,

What is the package that you are using? Diode losses are basically conduction losses. You can calculate the power dissipation by multipling the average current through the diode and the VF, and see if the package can handle that losses.

Thanks,

Youhao

0 lee peng kiat over 7 years ago in reply to Youhao Xi

Intellectual 450 points

Hi YouHao,

The package used diode is SOD128.
Max power dissipation can handle by diode is 750mW.
If = 1.6A & Vf = 390mW.
so the actual power dissipation = 624mW
The current rating for diode is enough ?

Thanks

0 Youhao Xi over 6 years ago in reply to lee peng kiat

TI__Guru* 78370 points

Hi lee peng kiat,

If your load current is only 1.6A, then the diode SOD128 should be okay. You may enlarge the Cathode pad size to help dissipate the heat.

Thanks,
Youhao

0 lee peng kiat over 6 years ago in reply to Youhao Xi

Intellectual 450 points

Hi Youhao,

Thanks

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LM25118: temperature for surrouding parts of LM25118