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UCC2808A-2Q1: about FB & COMP pins configuration for No Feedback Circuit

Paul Kim
Intellectual 1430 points
Part Number: UCC2808A-2Q1

Hi Team

I found my customer is using UCC2808A-2Q1 as below.

he don't use feedback due to board size limitation.

in this case, normally we connects FB to GND for Max Duty, and leaves COMP as floating.

however, he is using as below that FB is connected to between two 5.1Kohm.

my question is,,,

[Q1] at the below case, may I know what is error amplifier's output voltage ?

       and do you think the below H/W configuration will not cuase any abnormal operation by IC ?

[Q2] he is using Oscillator R = 11Kohm, C = 120pF.

        is IT OK for using ?

  • 0
    TI__Expert 3095 points
    Hi Paul Kim,
    Q1 The voltage on COMP pin will be 4.0V. For linear operation the two inputs of the amplifier must be the same, meaning the FB pin voltage must be 2.0V.
    Q2 I cannot recommend using an RT value less than 20k since this is outside the range given by the datasheet on Figure 13. If you request it I can ask the designers what is the expected result of using such a low RT resistor value, but it may take some time for us to get an answer.
    Thanks
    Joe Leisten