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UCC5350: Wiring of the driver BUCK circuit switch tube

Jackson Wu
Prodigy 20 points
Part Number: UCC5350
Other Parts Discussed in Thread: SN6501, UCC21551

I want to use UCC5350MC to drive the MOS transistor in the BUCK circuit, and I would like to ask:

(1) How do I connect the VEE pins on the secondary side of the chip? Can it be directly connected to the S-level MOSFET? (Because generally speaking, VEE needs to be grounded to a power source. If connected to an S-level, the VEE becomes a floating ground.)

(2) If possible, is it necessary to connect a resistor in series between S and VEE to avoid the impact of the switch on the driver chip.

(3) Is there a recommended application circuit diagram?

  • 0
    TI__Genius 14206 points

    Hi Jackson,

    Is this a synchronous buck converter with two FETS? A synchronous Buck works the same as a half-bridge.

    1. The output Vs- should be connected to the same net as the source pin of the FET that it is driving. You should minimize the inductance of this connection. On the high-side, Vee is floating on the switch node. You will need to attach the output Vs+ to a bootstrap supply or an isolated supply in order to keep Vs+ - Vs- >~18V to keep the high-side switch on.

    2. No, you want to keep the FET Vs and the UCC5350 Vs- (Vee?) equal as possible. Otherwise you might get transient overvoltages across the FET Vgs that could damage the gate.

    3.  We have dual-channel gate drivers for applications like this that have application circuits in their datasheets. The UCC21551 has a good example on page 1 and Figure 8-1 that uses a "bootstrap supply". Figure 8-2 shows an isolated bias supply partially. You would need a SN6501 or similar to provide the floating ideal voltage source shown.

    Best regards,

    Sean

  • 0 in reply to Sean Cashin
    Prodigy 20 points

    Thanks Sean，

    It is not a synchronous BUCK converter, there is only one MOSFFET in the circuit. So I need to use a single channel isolated driver UCC5350.

    As you said, can I just use an isolated power supply to power the driver and directly connect the VEE pin on the UCC5350 secondary side to the source of the MOSFET?