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TPS92641: TPS92641 output is abnormal

Amelie Zheng
Genius 10865 points
Part Number: TPS92641

Hi Team,

My customer now debug TPS92641 and meet some problem.

1.The input power is 12V, so according  to the formula, the output voltage should be 3.0V. However, the actual output voltage  is 3.578V in no-load state, and the  output voltage under the 12.5A electronic load is 3.3V. According to the LED PT-50 volt-ampere characteristic curve, when the current is 12.5a, the voltage is 3v. why the output voltage is not correct？

2.the swicthing frequency is 363.636khz according to the formula，but  the actual switching frequency is 578khz，The switch waveform is also abnormal，the switch waveform as follow;

3.At present, the actual carrying capacity of the current is only about 20A, but it can only last for a while. The MOS FET QLS will burn out immediately, also the TPS92641 will be damaged,The waveforms of HG and LG pins are measured as follows,according to my judgment, the HG and LG waveforms are abnormal,the MOSFET datasheet is attached

  • 0
    TI__Expert 3920 points

    Hi Amelie,

    This is a current regulator. It regulates to a load that deliver the current set by the IADJ regardless of voltage.

    Some LED runs 3 A at 3.3 V but some can run at 3 V or 4 V depending on the LED;s characteristic.

    As long as the regulated current is correct, you don't count on the voltage.

    For your second issue, it's double pulsing and I suspect there is some noise in the system makes it happened.

    And in such situation, FET might easily got damaged and hence affecting back to the TPS92641 device.

    I would suggest you to add a small capacitor (470 pF ~ 1 nF) close to CS pin to ground and see if this issue got cleared.

    Thank you!

  • 0 in reply to Issac Hsu
    TI__Genius 10865 points

    Hi Issac,

    Thanks for your quickly reply.

    As customer's feedback, they now don't connect with LED and they use electronic load to test.

    • When the electronic load is 2-3A, it is OK. However, when electronic load increase to >5A, it becomes really hot..
    • The burn mosfet is always LG. Actually customer has two High side mosfet and two low side mosfet in parallel. Does it make sense?
    • As for the waveform of HG and LG, it is also abnormal. It seems that it comes into overcurrent protection. Is it possible?
    • As for the waveform of SW, why system noise will lead to double pulsing?

    Could you please help for the above questions? 

    I will ask customer to try to add small cap. Thanks!

  • 0 in reply to Amelie Zheng
    TI__Expert 3920 points

    Hi Amelie,

    I will respond to your e-mail and we'll continue the discussion offline.

    Thank you!