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Original question:

TPS55340: Isolated Continuous Conduction Mode Flyback Using the TPS55340- SLVA559– January2013

TPS55340EVM-148: Problem with Output Voltage 15 V

Hans Georg Wolf
Prodigy 70 points
Part Number: TPS55340EVM-148
Other Parts Discussed in Thread: TL431, TPS55340, , TLV431

We bought the evaluation board TPS55340EVM and want 15V as output voltage, the input voltage is about 12V. For this we have installed the reference TL431 and changed the resistor R14. At the output, however, there is only approx. 3V. What can be the reason for this?

  • 0
    TI__Expert 7450 points

    Hi Hans,

    Thanks for your interest in TPS55340.

    What is your load? What is the R14 you changed and do you have the waveform for COMP?

    Thanks,
    Yinsong

  • 0 in reply to Yinsong Cai1
    Prodigy 70 points

    Hi Yinsong,

    Thank you for your answer and helpfulness.

    we have the original TPS55340EVM-148 Evaluation board without an extra load. The value of R14 was calculated using Equation 27 from SLVA559 to R14=6.02k (Vout=15V and Vref = 2.5V from TL431). The signal for comp is not a waveform, it is relatively exactly 1V DC.

    Thanks

    Hans

  • 0 in reply to Hans Georg Wolf
    TI__Expert 7450 points

    Hi Hans,

    Thanks for the information.

    Do you see any switching behavior (SW node voltage)? It seems the COMP is clamped low.

    Thanks,
    Yinsong

  • 0 in reply to Yinsong Cai1
    Prodigy 70 points

    Hi Yinsong,

    please excuse my long time for the answer. Yes, the COMP was clamped low. As mentioned on page 9 in the PDF SLVA559 from TI we changed the TLV431 to TL431 for the desired higher output voltage of 15V. As we noticed later the TLV431 and the TL431 are not pin compatible, unfortunately there was no hint to the different footprints in the PDF. After we installed the TL431 with manual wiring on the evaluation board, there was a signal at COMP and the output voltage rose.

    Immediately afterwards, there was a short smoke and the current limitation on the power supply became active. The output capacitors C6 and C8 on the evaluation board were unfortunately only 10V types, and there was no reference to this in the TI document. Unfortunately, the TPS55340 broke due to the defect of the output capacitors. After we replaced the TPS55340 and the capacitors, the evaluation board worked well and provided the desired 15V at the output.
    The TPS55340 seems to be very good IC, but the TI documentation for the evaluation board lacks some clues, which is not a good thing.
    Thank you for your helpfulness and best regards
    Hans
  • 0 in reply to Hans Georg Wolf
    TI__Expert 7450 points

    Hi Hans,

    Thank you for your valuable comment. We will try to improve this.

    The output cap voltage rating are listed in the table 4 BOM of the userguide.

    Again, thank you for your patience and your selection of TPS55340.

    Best,

    Yinsong

  • 0 in reply to Yinsong Cai1
    Prodigy 70 points

    Hi Yinsong,

    thanks for your answer and Kind Regards

    Hans