LM3406HV: LM3406HV: Temperature problem.

mst er

Prodigy 110 points

Part Number: LM3406HV
Other Parts Discussed in Thread: LM3406,

I'm using lm3406 in my led driver project. I'm having a temperature problem. Parameters of the circuit:

Fswitching: 500kHz

Output Current:0.7A

Input Voltage:48V DC

Output Voltage 40V DC

My circuit is LM3406 datasheet typical application. Circuit components calculated by application note. Why LM3406 IC rised temperature?

over 5 years ago

0 Irwin Nederbragt over 5 years ago

TI__Mastermind 28655 points

Hello,

What do you mean by temperature problem? At 0.7A and over 80% duty cycle there is some conduction loss. There will be switching loss as well at 500 KHz. The part is intended to do this and will rise in temperature. The LM3406 has an exposed pad for heatsinking, what have you provided for heatsinking the LM3406? How large is your PCB pad for removing heat from the LM3406. Does the pad have vias to pull heat to another plane?

Best Regards,

0 mst er over 5 years ago in reply to Irwin Nederbragt

Prodigy 110 points

Thanks for answer. My PCB properties

1-LM3406 has not via

2- My PCB temperature normal

3- I am gonna try big LM3406 thermal pad and %50 duty,200kHz

I hope this problem fix

0 Irwin Nederbragt over 5 years ago in reply to mst er

TI__Mastermind 28655 points

Hello,

If your output is 40V and input is 48V the duty cycle is determined, approximately 40V/48V (not including losses), or 83%.

It will work with your specifications if it has a decent thermal connection to the bottom pad.

You can look at the LM3406HV EVM. It runs at 500 KHz, up to 1.5A. It has thermal vias to the bottom side of the board.

Best Regards,

0 mst er over 5 years ago in reply to Irwin Nederbragt

Prodigy 110 points

My project circuit LED Driver LM3406HV still have temperature problem. Maybe the task cycle is 50% and fsw = 200kHz to troubleshoot this problem. Thanks.

0 Irwin Nederbragt over 5 years ago in reply to mst er

TI__Mastermind 28655 points

Hello,

I haven’t heard back from you, I’m assuming you were able to resolve your issue.
If not, just post a reply below (or create a new thread if the thread has locked due to time-out)

Also, make sure you are using a schottky diode for the freewheel diode, or a diode capable of high frequency operation. Using the wrong diode can cause excess heat in the LM3406, D1 in the typical application diagram 3.1 of the datasheet on page one.

Best Regards,

0 mst er over 5 years ago in reply to Irwin Nederbragt

Prodigy 110 points

Thanks for answer. I solved the problem by designing new cards

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LM3406HV: LM3406HV: Temperature problem.