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TPS54620: Regarding the OVP of TPS54620

Kyohei
Expert 1871 points
Part Number: TPS54620


Hi team,

 

My customer is using the TPS54620, and we are experiencing power startup failures at low temperatures. Could you please review the following?

Conditions

  • Input voltage: 14 V

  • Output voltage: 0.95 V

  • Output current: 6 A

  • Temperature range where the issue occurs: –10 °C to 5 °C

Symptom

  • PWRGD drops due to OVP

Verification

  • Changed constants on the COMP pin

    • R2440: 3.3 kohm → 1 kohm

    • C2458: 0.01 µF → 0.047 µF

  • Result: No symptom observed

  • Phase margin of the board at room temperature (before change): 32°

  • Phase margin after change: 66°

Our view We are concerned that excessive overall loop gain and insufficient phase margin allow load transients or switching noise to be superimposed on Vsense, causing the output to overshoot transiently. As a result, PWRGD goes outside the range of 94% Vref < PWRGD < 106% Vref, which we believe triggers the Fault condition.

Question We would like to hear TI’s view regarding this phenomenon.

Best regards,

Kyohei

  • 0
    TI__Expert 5838 points

    Hi Kyohei,

    Based on your experiment changing COMP components, we can pinpoint to where the issue is coming from. The part itself is rated for –40°C to 150°C Operating Junction Temperature so most likely at –10 °C to 5 °C ambient temp, it should be ok for the IC itself. Now the issue is probably coming from external components not properly tuned and changing with temp. COMP is a very sensitive pin so noise or wrong components can severely affect the device output regulation.

    A phase margin of 32 is low and considered unstable. You always want to aim for at least 45 ° to account for different changes the device could go through like temp or aging. 

    During non-ideal temps (outside ambient), components like cout, comp network, fsw R and FB R can shift, making the system even more unstable which aligns with your device behavior.   

  • 0 in reply to Eileen Hernandez Hernandez
    Expert 1871 points

    Hi Eileen-san,

    Thank you for your confirmation.

    After sharing the information with our customer, they raised an additional question as follows:

    Question: “You mentioned that temperature and aging need to be taken into consideration. Could you please provide detailed guidance on which specific parameters change and how they change?”

    Best regards,

    Kyohei

  • 0 in reply to Kyohei
    TI__Expert 5838 points

    Hi Kyohei,

    Temperature and aging can affect the component's electrical characteristics (value, ESR and DCR). This is more for caps and inductors.

    Our device has been tested to operate withing datasheet temp specs, so with that line I was referring to external components particularly COMP passives.  

    However you observed improvement by changing COMP values regardless of temp, so I would focus on that. COMP pin is very sensitive and can shift the stability of the device so what you observed makes sense.