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TPS62130: TPS62130 obtained very high overshoot during start up

Ee Wen Quek
Intellectual 300 points
Part Number: TPS62130
Other Parts Discussed in Thread: TPS61230

Hi,

I am designing TPS62130 with switching frequency of 1.25MHz, Vout =4.2V. FSW is tied to Vout in this case. I noticed there is a large overhoot during the start up. The positive overshoot reaches +6.2V. Is there any design issue that can cause such behavior? The SS pin is tied to 0.01uF. Thanks

  • 0
    TI__Genius 14876 points

    Hello,

    Can you provide the schematic you are using for your application as well as a scope shot of the behavior you are seeing?

    What are exactly the operating conditions of your system? (Vin and Load)

    I also recommend you to have a look at the newer, smaller and newer TPS62147/8 which offer a bit lower Iq, some extra features, and tighter output accuracy.

    Thank you!

    Best Regards,

    Dorian

  • 0
    Intellectual 470 points

    Hello,

    Can you share the schematics and test conditions.

    I too encountered a similar problem with a boost converter long back. Reason was, I was operating it in a no load condition. The inductive kickback on the low side FET was blowing up my circuit.

    Try adding a bleeder resistance or a small TVS/ Zener diode on the output. The TVS and Zener should be appropriately chosen so that it's not clamping during normal use. A 5V TVS/ Zener would work provided the circuitry ahead of the supply doesn't get damaged.

    The absolute maximum for the SW pin is 7V and you've reached 6.2 which is dangerously close to the limits for the low side switch. Going beyond 7V on SW pin will damage the low side FET channel.

    Thanks and Regards,

    Avish

  • 0 in reply to Dorian Brillet de Cande
    Intellectual 300 points

    Operating condition: Vin=+12V, Test Load=0.1A & 1A

    My Schematic: 

    My oscilloscope result when measuring rise time and overshoot at output:

    Weird waveform at switching node:

    My thought is that when the output voltage is insufficient / havent output 4.2V, FSW=2.5MHz? Until the point where 4.2V or desired output reached, FSW=1.25MHz.  But not sure why interval there is a weird pattern retrieved as shown in picture. Is there sth wrong in my design?

  • 0 in reply to Avish Gupta
    Intellectual 300 points

    Hi,

    Yea  I did add bleeding resistor in my design. I saw the datasheet mentioned the SW node max rating is Vin+0.3V, my board is still working but obtained a very high overshoot. 

    Thanks.

  • 0 in reply to Ee Wen Quek
    Intellectual 470 points

    Hi,

    In your first post, you mentioned TPS61230, later you mentioned TPS62130.

    Both are very different topologies and devices.

    I'll get back after studying 62130

    Thanks and Regards,

    Avish

  • 0 in reply to Avish Gupta
    Intellectual 300 points

    Sorry, i didnt noticed the mistake in typing. I am using TPS62130

  • 0 in reply to Ee Wen Quek
    Intellectual 470 points

    Hi,

    If you see the width of that overshoot, it's roughly 5ms which is also equal to the soft start time set by the timing cap Css.

    Try reducing the value of Css or simply remove it and check.

    Thanks and Regards,

    Avish

  • 0 in reply to Avish Gupta
    Intellectual 300 points

    Hi,

    I did suspect on SS/TR so i also try to reduce to 3900pF. The waveform obtained seems like it still 5ms overshoot time. 

    Yellow; Switching node, Blue: Output voltage during start-up

  • 0 in reply to Ee Wen Quek
    TI__Genius 14876 points

    Hello,

    Before we have to go further in any investigations. I think it is essential that your FSW pin is tied to a constant value and not VOUT which goes from logic state low to a logic state high. If you could apply either VIN or a voltage greater than 0.65V on FSW it would really helpful.

    Thank you very much!

    Regards,

    Dorian

  • 0 in reply to Dorian Brillet de Cande
    TI__Genius 14876 points

    Hello,

    I haven't heard back from you. Were you able to make any changes in your design to have FSW tied to a high logic state?

    If yes, did it fix your issue?

    Thank you !

    Best Regards,

    Dorian 

  • 0 in reply to Dorian Brillet de Cande
    Intellectual 300 points

    Hi, 

    Sorry for late reply. I have fixed the issue. There is nothing related with the design for the overshoot issue. We are suspecting we turn on the enable first before the Vin is come in, after trying a few time in such way, the IC get burn. We have try rework and power up with Vin come before EN, there is no overshoot issue appear. Thanks for helping to fix the issue.