LM2678 Heating

Andi Zaganjori

Other Parts Discussed in Thread: LM2678

Hi,

I am using the LM2678 to convert a 12V input to a 8V (5A). The problems I have is heat and noise. When I apply a load of 3Amps or more the IC heats up switches off. Any suggestions? I used the same components and schematic as the schematic from WEBENCH below.

Regards
Andi

over 10 years ago

0 Peter Meaney over 10 years ago

TI__Mastermind 31580 points

Hi Andi,

I have moved your post the non-isolated dc/dc forum.

Regards

Peter

0 Akshay Mehta over 10 years ago

TI__Genius 15810 points

Hello,
What package are you using for LM2678? Have you soldered the thermal pad of the IC to the ground plane? Would you please share your layout?
Regards,
Akshay

0 Andi Zaganjori over 10 years ago in reply to Akshay Mehta

Prodigy 80 points

Hi,

Thnx for the fast reply. I am using a TO-263 package. It seems like I solve the heating problem, at least for the moment (I added a bigger heatsink). Another problem I have is that from the design posted above I don't get 5A, I get 3A. Any idea whats the problem there?

Thanks a lot and Regards
Andi

0 Andi Zaganjori over 10 years ago in reply to Andi Zaganjori

Prodigy 80 points

ps: I don't have a layout for the moment. I am testing my Idea on a Stripboard (picture below). The voltage divider and the output capacitor are on the bottom side :) The IC is on the left side of the picture connected by the yellow wires.

0 Akshay Mehta over 10 years ago in reply to Andi Zaganjori

TI__Genius 15810 points

Hello,

The LM2678 and other DCDC regulators have high switching frequencies. This makes it important to have a good layout. When you have long wires and bigger loops, the act as antennae and can couple a lot of noise on the sensitive nodes as the FB. Please look at the EVM for examples of good layout. You need to absolutely keep the diode and the input bypass cap close to the VIN and GND pins of the IC and on the same plane. Do not introduce vias there. The SW node should be short, fat and wide. Long wire connections will introduce parasitic inductance and cause spiking which could potentially harm the device.

Regards,

Akshay

0 Andi Zaganjori over 10 years ago in reply to Akshay Mehta

Prodigy 80 points

Hello,

Thank you for the helpful reply:

Regards
Andi

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LM2678 Heating