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LM73606: Thermal Stress with pulsed output instead of steady-state?

Alpha H
Genius 10855 points
Part Number: LM73606

Hi team,

I have a question regarding the LM73606 power/thermal characteristics in pulsed mode.

If I'm going from Vin 28VDC, ~1.6A --> 7.5V @ 5A, but with a pulsed output ,(~0.3ms pulse), do you see any concerns overstressing the device?

I looked at the datasheet and the max junction temperature is 125C.  In steady state, it looks like I would be exceeding Tj when multiplying power loss * Rthetaja.

However, how does this change with a pulsed output?

If the device is still overstressed, do we have any sync-buck with integrated switches that could work instead?

Thanks for the help team, I really appreciate the support!

-Arthur Huang

  • 0
    TI__Mastermind 25590 points

    Arthur,

    The theta parameters are not often very reliable in any datasheet due to the standard by which it's measured and the highly variable type of IC that's available today. The best way to gauge thermal performance is to take a look at the EVM and see what it does on a real board.

    The EVM user guide shows the board is 90% efficient at 5VOUT, 6AOUT (30WOUT) and the thermal image shows an ambient of ~23C with an IC temp ~55.4C which gives us a more reasonable ~10C/W for the whole board. So provided your layout is on par with the EVM you could expect about 4W of power dissipation with an increase of about 40-50C from ambient.

    But that assumes you're running a continuous 7.5VOUT with 5AOUT. If you have a pulsed output then the effective (average) output will be what you need to consider for thermals. Take the duty cycle of the load (0.3ms / time off) and multiply it by 37.5W (7.5V*5A) to get the effective power out. Then divide the effective power by 90% (~efficiency) to get PIN. Then take PIN - POUT to find the power dissipated by the IC and multiply by ~10C/W to get your approximate temp while you're running your pulsed load.

    *Note: The number you get will be the average. You still have to consider the peak which would be right at the end of the 0.3ms pulse. But that probably won't make or break your design.

    -Sam