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UCC27289: For two switch application

Part Number: UCC27289
Other Parts Discussed in Thread: UCC27714


Can the UCC27289 use on the two switches topology?

There has another power for the HB pin, and the switch turns on together.

thanks and best regards

  • Hello Rock,

    • The UCC27289 can be used for a 2 switch forward and there is a consideration for ensuring the HB capacitor can be charged with the bootstrap bias method. The UCC27714 datasheet Figure 49 shows an external transistor circuit which will allow the HB bias capacitor to be charged during the power switch off times. The resistor shown in series with the boot diode cannot be used with the UCC27289 and a resistor needs to be added from VDD to the auxiliary switches drain and gate connection.


  • Hi Richard

    Can UCC27289 use the same circuit as UCC27714 datasheet Figure 49? My customer has PCB size considerations.
    And could you also explain the operation principle of the datasheet Figure 49, thanks


  • Hello Rock,

    The circuit in the UCC27714 can be used, the boot diode shown in the diagram would not be installed, as the UCC27289 has an internal boot diode.

    The principle is the driver low side output when turned off turns off the aux transistor (bottom switch) which allows the aux transistor top switch to turn on. The aux switch (top) turning on provides a path for the driver HS to be pulled to ground which provides a charging path for the bootstrap capacitor to charge from VDD through the boot diode. 

    During the power switch off time, the HS is pulled low allowing the boot cap to charge.