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UCC28C44

johnliang
Intellectual 505 points
Other Parts Discussed in Thread: UCC28C44

What is the minimum working voltage parameter value of the ucc28c44 ?   I can not find the value in the UCC28C44.pdf 

  • 0
    TI__Mastermind 40520 points
    Hello John,

    The Under-voltage Lockout section of the datasheet specification table on page 6 indicates that the VDDoff level for the UCCx8C44 is typically 9 V +/- 1V. I recommend to keep it above 10V to allow for lot-to-lot and temperature tolerances.

    If you are asking about a minimum system input voltage, there is no spec for that. If you can keep the VDD input of the UCC28C44 above VDDoff (after first exceeding VDDon to start-up) the controller will control the converter at any minimum input voltage provided that the converter is designed to operate at that voltage. In other words, the controller does not limit the minimum input voltage for the converter. That is a function of the converter design.

    I hope this answers your question.
    Regards,
    Ulrich
  • 0 in reply to Ulrich Goerke
    Prodigy 140 points

    Hello Ulrich goerke,

    I'm using UCC28C44 for dc-dc converter application. The auxiliary winding powers the device after the start-up. But the voltage is not pure dc but half wave rectified. Here how does the controller generates pulses to the MOSFET? And also i have a doubt that if the voltage to power UCC28C44 is pulsating does this allow the start-up circuit to work throughout the application? Your suggestion would greatly support me.

    Regards,

    deepika

  • 0 in reply to naga mani deepika basa
    TI__Mastermind 40520 points

    Hello Deepika,

    Please refer to the UCC28C44 datasheet Figure 31 on page 24; you'll see that this converter design example also uses an auxiliary winding for the controller bias power.  The diode rectifies the winding voltage during the "flyback" interval of the switching cycle.  During this time the VDD capacitor Cvdd peak-charges to the winding voltage.  This voltage is a one-to-one reflection of the output voltage, so it is about 12V.  Cvdd holds this voltage during the primary switching interval and dead times of the switching cycles, so there is no pulsating voltage on VDD.  It is a smooth dc level of 12V.

    The start-up resistor, in this case, is always "on" the entire time the converter is operating, but the current through this resistor is very low so the power dissipation is small.  The start-up VDD current of the UCC28C44 (Istart-up) is less than 100uA, so the start-up resistor Rstart only needs to provide a little more than that to charge up Cvdd.  After switching begins, Ivdd increases to several mA, but that power is now provided by the auxiliary winding, even though Rstart is still conducting a few hundred uA.   

    I hope this answers your questions.

    Regard,
    Ulrich

  • 0 in reply to Ulrich Goerke
    Prodigy 140 points
    Thank you so much Mr. Ulrich