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LM5175: I have some Question about LM5175 and Dual Power Mosfet.

yoonju hwang1
Prodigy 110 points
Part Number: LM5175
Other Parts Discussed in Thread: CSD87353Q5D

Hello!, I have some Question about LM5175 and Dual Power Mosfet.

I develop the Buck-Boost Power Module using the LM5175 IC. this is very work well.

<Buck-Boost Power Module Spec of My Mainboard>

1. Input : 9V~36V

2. Output Voltage : 12V

3. Output Current : 5A

4. Mode : DCM + Hiccup Enable.

5. SW freq : 330KHz

** I have to design the Mainboard and i will on-board design the LM5175 Power System.

And the main board size I designed is a small form-factor. That's why small form-factor size components should be used to reduce the main board size.

<Question>

1. It is okay about i using the dual Power Mosfet in LM5175 Power schematic?

2. Are there any dual Mosfet (Ti Vendor) products to recommend?

** Currently, My LM5175 schematic designed single Power Mosfet *4 EA, in the my Mainboard.

so i would like exchanged single power Mosfet to Dual Power Mosfet(Ti Vendor)

If you give me a reply, i really appreciate.

Thank you!

  • 0
    TI__Guru 58215 points

    Hello Yoonju,

    1. It is ok to use 2 dual MOSFETs, as long as you make sure that the power dissipation can be handled by the package.

    2. Let me send this question to the TI expert on MOSFETs.

  • 0 in reply to Brigitte
    TI__Expert 6835 points

    Yoonju,

    Our applications expert is out until Monday, he will look at this then.

  • 0 in reply to Chris Bull
    TI__Mastermind 29525 points

    Hi Yoonju,

    Thanks again for your interest in TI products. For the buck FETs, the only dual, 60V devices in our portfolio are in an SO8 package and the on resistance is too high for your application. For the lower voltage boost FETs, we have power blocks with stacked die in a half-bridge configuration. Assuming these FETs should be roughly symmetric (same or nearly same on resistance), the only product that may work is the CSD87353Q5D with typical 2.8mOhm top FET and 2.1mOhm bottom FET. This is much higher on resistance than the FETs used on the LM5175 EVM and will result in unacceptable power loss.

    The power block has been optimized and characterized for synchronous buck applications. It has not been evaluated in a buck-boost converter with the LM5175 controller. We have tested some of our discrete FETs with this controller. Because our FETs switch very fast and have a "snappy" body diode, we were seeing negative voltage spikes that exceeded the abs max ratings of the controller. In order to protect the controller, external components had to be added to slow down the FETs which increased the power loss resulting in lower efficiency and more heat to dissipate.

    That being said, I do not believe we have good dual FET solutions to recommend for your application.

    Thanks,

    John Wallace

    TI FET Applications