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TPS40170 - 24V/20A DC power supply

Hung Tran
Prodigy 50 points
Other Parts Discussed in Thread: TPS40170

Hi

I'm considering TPS40170 for 24V/20A DC power supply. Referring to PMP6703 which is a half in power, I see it has 4 Mosfet , 2 mosfet per side (low and high).

Can you tell me advantage of using double mosfet ?

Any suggestion for me to design this app?

the PCB Layout must be in 4 layer like in EVM? can I do this in 2 layer?

regards

Hung

  • 0
    TI__Mastermind 35185 points

    Hi Hung,

    This design uses two MOSFETs for the high-side and low-side to increase efficiency and reduce power dissipated in each MOSFET individually. If a single MOSFET is used the power supply will run very hot.

    I recommend using a 4 layer board with an identical layout to PMP6703 (or PMP6680, the PCB this design was built on).

    Best Regards,
    Anthony

  • 0 in reply to Anthony F
    TI__Mastermind 35185 points

    Here's a link to the layout: http://www.ti.com.cn/cn/lit/ug/slur303/slur303.pdf

  • 0 in reply to Anthony F
    Prodigy 50 points

    Hi Anthony

    Thanks for your reply PMP6703 using minimum switching frequency of 100khz

    is there any problem if it runs with 300kHz?

    in addition, my app run at 15A in 1 second then keep staying at 100mA.

    regards

  • 0 in reply to Hung Tran
    TI__Mastermind 35185 points

    At 300kHz three times the current is needed for gate drive of the FETs. This also increases loss in the internal LDO by approximately 3x. The higher switching frequency can cause the TPS40170 to operate at very high temperatures. What is the input voltage for your app?

  • 0 in reply to Anthony F
    Prodigy 50 points

    input voltage for my app is normally 48V (42V-58V) if using 100khz switching frequency the inductor very big costing much

    only temperature issue?

    current for gate driver is automatically control according to frequency?

    regards

  • 0 in reply to Hung Tran
    TI__Mastermind 35185 points

    The average gate drive current is estimated by Qg*fsw, so a higher switching frequency increases the current needed. The power loss internal to the TPS40170 due to the gate drive is VIN*Qg*fsw. With higher VIN, higher fsw and higher gate charge FETs the power loss increases.

    With these high power levels (high input voltage and high output current), a low switching frequency is often needed to ensure the components do not operate at too high of a temperature.

    Best Regards,
    Anthony