• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 63 subscribers
  • Views 405 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS43060 efficiency and MOSFET selection

York
Prodigy 180 points
Other Parts Discussed in Thread: TPS43060, LM5002, LM5001

I'm experiencing low efficiency when boosting 24V to 50V @0.25A via TPS43060. The chip gets hot and the efficiency never exceeds 80%, and especially low at lower current. And the chip gets very hot after a while.

After some research, i decided it was my MOSFET's gate driver sinks some of the current. The mosfet i choose is Vishay's SUD25N15, which has a total gate charge of 30nC at 7V, and i used it for both high-side and low side.

The frequency is about 600KHz and here's how i calculate the gate drive current:

Igdrv = 600kHz * 30nC * 2  = 36mA.

and this current comes from VCC pin of the chip, which regulates at 7V from the 24V supply. This alone will contribute the chip's power dissipation:

(24-7)V * 36mA = 0.612W

which i think, is why the chip gets very hot.

Talking about MOSFET selection, i get too little details from the datasheet.  I want to know how the selection of High-side and Low-side MOSFET differs?

  • 0
    TI__Genius 13700 points

    Hello York,

    You can adjust your MOSFET section based on expected duty cycle but rather than discuss MOSFET selection. Yes it looks like you are dissipating a considerable amount on power on your control compared to the power you are converting.

    I would recommend looking at the FETs with a lower gate charge especially since you are switching at 600kHz. You also need to take into account that the TPS43060 has to sink the power output of the gate capacitance which makes the power calculation that the driver is dissipating even greater. 

    But based on the parameters of your converter and the cost and size of the SUD25N15 would you be open to considering an integrated switch solution? You could look at something like the LM5002 which has integrated switches and reduce your solution cost, increase your efficiency 10%, reduce your component count and power supply size with no external switches and smaller inductor. 

    You can also look to see what other options are available. Have you tried using WEBENCH for a solution? This tool lets you define you input and output parameters and then provides with solutions that either focus on price, solution size, or efficiency. These designs then provide you with a recommended BOM for the converter and allow you to adjust the components and looks at supply simulations. 

    Ryan May

  • 0 in reply to Ryan May
    Prodigy 180 points

    Thanks, Ryan, for your detailed answers.

    Yes i did consider using an intergrated switch version like LM5001, but when i type my requirements in the TIs Webench, this chip give me the best efficiency, which, of course, is based on a very low gate charge MOSFET and an ideal "CUSTOM" inductor (only a few mili-ohms DCR, which would be impossiblly bulky) . which i neglet at first glance.

    Another reason i choose TPS43060 is this chip gives higher temperature tolerance, 150 celcius compared to 125 of LM5001.

    The cost is not too sensitive in my application, but efficiency really matters.

    I also tried to lower the switching frequency as low as 50Khz of my TPS43060 circuit, but it still didn't offer much improvement. The chip's still very hot.

    In order to be able to use the same circuit board, i decided to try a different MOSFET, the fairchild's FDD86252, which as the lowest possible gate charge with the same package, TO-252

    I'm coming back soon...