UCC38086: Short circuit not working

Part Number: UCC38086

Hi,

I have used UC38086 pwm controller to design a pushpull conveter. While doing the short circuit test, the ic is not going to hiccup mode and input power is taking on output short circuit. Can you suggest a soultion?

Regards,

Aswathy

  • Aswathy,

    Thanks for connecting through E2E. It is an excellent forum for Engineers to learn from each other and it works best when problems and recommended solutions are stated as clearly as possible. TI appreciates and values every thread entry into E2E but yours needs more information to benefit yourself and others who visit E2E. Your question can only be answered with more questions: 

    1. What are the converter design specs: VIN, VOUT, POUT, Fsw?
    2. What kind of short circuit is introduced to the converter? E-Load, mechanical short, soft overload, etc? 
    3. How is the converter behaving in response to the short circuit load condition? Waveforms and a detailed description would be helpful here.
    4. How does the converter behave when the load is increased softly from 100% to >100+% rated load current?
    5. What is the measured RCS waveform compared to the CS pin of the UC38086? Verify the appropriate values of the RC filter components?
    6. What does the CS pin, VOUT of the converter and CTRL look like during the short circuit condition?

    Regards,

    Steve M

  • Hi Steve,

    Please see comments below

    1. What are the converter design specs: VIN, VOUT, POUT, Fsw? 15Vdc, 150Vdc, 110W, 100kHz
    2. What kind of short circuit is introduced to the converter? E-Load, mechanical short, soft overload, etc? mechanical short at the output.
    3. How is the converter behaving in response to the short circuit load condition? Waveforms and a detailed description would be helpful here. During short circuit at the output, from input, converter is taking 40W power continuously. IC not going to hiccup mode.
    4. How does the converter behave when the load is increased softly from 100% to >100+% rated load current? Overloaded the output up to 150%, then after 120%, regulation is going out slightly. But the unit is working fine. Overloaded and kept the unit for 5 minutes only. 
    5. What is the measured RCS waveform compared to the CS pin of the UC38086? Verify the appropriate values of the RC filter components? RC value is 1K & 470pF. Rsense is 20mE/3W
    6. What does the CS pin, VOUT of the converter and CTRL look like during the short circuit condition? Vout is 0V. 

    I have tried tuning, Rsense, RC of CS pin, Iset pin resistor & CTRL pin resistor, output inductor. Then, also IC is not going to hiccup mode on short circuit.  Do you have any suggestions on these values? Which is the most critical Item among these, to make the short circuit work?

  • Hi Steve,

    Please see comments below

    1. What are the converter design specs: VIN, VOUT, POUT, Fsw? 15Vdc, 150Vdc, 110W, 100kHz
    2. What kind of short circuit is introduced to the converter? E-Load, mechanical short, soft overload, etc? mechanical short at the output.
    3. How is the converter behaving in response to the short circuit load condition? Waveforms and a detailed description would be helpful here. During short circuit at the output, from input, converter is taking 40W power continuously. IC not going to hiccup mode.
    4. How does the converter behave when the load is increased softly from 100% to >100+% rated load current? Overloaded the output up to 150%, then after 120%, regulation is going out slightly. But the unit is working fine. Overloaded and kept the unit for 5 minutes only. 
    5. What is the measured RCS waveform compared to the CS pin of the UC38086? Verify the appropriate values of the RC filter components? RC value is 1K & 470pF. Rsense is 20mE/3W
    6. What does the CS pin, VOUT of the converter and CTRL look like during the short circuit condition? Vout is 0V. 

    I have tried tuning, Rsense, RC of CS pin, Iset pin resistor & CTRL pin resistor, output inductor. Then, also IC is not going to hiccup mode on short circuit.  Do you have any suggestions on these values? Which is the most critical Item among these, to make the short circuit work?

  • Aswathy,

    You have not provided any waveforms, so I can only make "best guesses" what might be happening? It sounds like the current is folding back into a power limit. If you are referring to "hiccup mode" as try/retry after a number of counted clock cycles, I don't believe UCC38086 has this feature?  Please see attached for help.

    Regards,

    Steve