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Original question:

TPS40210: PMP4540 questions

TPS40210: PMP4540 questions

Minami
Prodigy 30 points
Part Number: TPS40210
Other Parts Discussed in Thread: LM3478, LM5155, LM5122

Hi experts,

We got a question about PMP4540(Boost TPS40210)followings.
www.ti.com/.../pmp4540

Could you check it and give us feedback?

Q1)
I don't understand that VBP-pin supplies power to the MOSFET.
I think that GDRV-pin can supplies power to the MOSFET.

My idea is as follows :
Limit average current of GDRV-pin is 400mA.
Total gate charge Qg of SUP60N06-12P is 55nC.
Switching frequency fsw is 100kHz.
Thus, the average of gate current is Qg×fsw=5.5mA
Therefore, I think GDRV-pin can supplies power to the MOSFET.
Why GDRV-pin is not strong enough to drive the large MOSFET?

  • 0
    TI__Guru* 78070 points
    Hi Minami,

    Please refer to a text book for the MOSFET driver circuit, and for how the MOSFET is turned on and off. VBP is the bias supply pin to supply the driver, and the GDRV is the driver output pin. VBP should be stable dc voltage while GDRV is pulsing. The 400mA is the peak current, and the 5.5mA that you calculated is the average dc current of needed from the driver. The GDRV voltage looks like a square wave with rounded rising and falling edges, but the driver current is a narrow pulse aligned with the GRDV rising and falling edges. The current only flows in and out of the MOSFET gate during the ~100ns period at turn-on and turn-off transient. The 400mA limit is the peak of the gate drive current pules' peak value.

    The 400mA is not a very strong driver. We have other stronger controllers like the LM3478/81 which has 1A peak, and a new device the LM5155 having 1.5A peak. The sync boost controller the LM5122 has 3A peak drivers. The stronger, the short time the turn-on and turn-off can be to save switching losses, but it is also more expensive to make a stronger driver. For the TPS40210, the 400mA pk driver is just adequate for the applications which it targets at.

    Hope this clarify.

    Thanks,
    Youhao