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LM3406HV: heat temp

Raymond He
Expert 1990 points
Part Number: LM3406HV
Other Parts Discussed in Thread: LM3406

dear

LM3406HV turns on for 1 minute, IC heats up to 70 degrees

 

Questions are as follows:

LM3406HV applications are as follows:

Input: 60V

Output: 54V 1.3A COB LED

 When the RON resistance is set to 150K, the frequency is about 430K, and the LM3406HV heats up severely and the temperature is below 90 degrees.

 When the RON resistance is set to 300K, the frequency is about 300K, and the heating temperature of LM3406HV is about 70 degrees.

 Excuse me, can LM3406HV achieve 60W? How big should the RON resistance be set? What is the appropriate frequency setting?

 How to solve the heating temperature of this LM3606HV?

Can I set the frequency to 120KHZ?

  • 0 in reply to Raymond He
    TI__Mastermind 28655 points

    Hello Raymond,

    Lowering the switching frequency will reduce switching loss.  You also have conduction loss.  At 54V output 60V input duty cycle is high.  Rdson is 370 mohm typical 750 mohm maximum.  conduction loss at room temperature typical will be 0.37 ohm * 1.3A ^2 * duty cycle which will be over 90%, this will be over 600 mW.  At higher temperature the Rdson will get closer to 750 mohm.  At higher power levels the LM3406 heatsinking needs to be increased, more copper plane under the part with thermal vias to pull heat away from the part.  Reducing switching frequency will reduce the temperature but power will have to be dissipated.  As an example, at 95% efficiency over three watts of power will be dissipated by the buck converter components.

    As for reducing switching frequency, the design calculation need to be done to calculate the correct inductor value as well as other components.

    Best Regards,