• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 549 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC283t Adj resistor and potentiometer values

Adam Crow
Prodigy 10 points

I am trying to wire up a UCC283t adj as an adjustable power regulator with a Vin of roughly 7.2v using 2 14500 Li-Ion batteries. I would like to have an adjustable range of 3.7v to 7v using a potentiometer but I can't make heads or tails of the Data sheet. Any assistance that could be rendered to help me figure out what resistors and potentiometer I would need to achieve this and if capacitors are required would be greatly appreciated.

  • 0
    TI__Expert 8890 points

    Hi Adam,

    I see what you mean. Use the ADJ version of the part.  The adjustable version will not have the internal feedback resistors, R2 and R1,  shown in the Functional Block Diagram.  You will need to provide these resistors externally and I suggest that R1 = 50kohms and that R2 be your potentiometer (3.7V - 98kohms, 7.2V - 238kohms). The node between the resistors will be connected to the ADJ-pin of the part.  This output voltage is adjusted in accord with equation on page 5 of the data sheet:

    Vout = 1.25 x ((R2 + R1)/R1)

    Figure 5 of the data sheet gives an application diagram where the input and the output capacitors are 10uF ceramic.  I would go with these values.  

    This part also requires a short circuit delay timer capacitor, CT.  The data sheet warns that if the startup time to charge the output capacitor exceeds the short circuit delay than the startup will be determined to be a short circuit - and the LDO will not start properly.  So you will need to make this CT capacitor large enough to allow for a successful startup. The equation given in the pin descriptions indicates that a for a short circuit delay time of  0.75ms - 1.65ms then the CT cap would be between 1nF and 2.2nF. These capacitances should allow for a successful startup - though you can increase the capacitance (dramatically) if needed.

    Regards

    Bill