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TPS53353: TPS53353 VBST-LL exceed the standard

user6304695
Prodigy 120 points
Part Number: TPS53353

Tool/software:

Hello：

       I have encountered a problem, could you please help me answer it.

TPS53353，VIN=12V，Vout=1.2V，Iout max=16A; oscilloscope use High voltage differential probe measurement，bandwidth=500MHz。

  

1）Rbst=5ohm，Cbst=0.1uF at 16A load，test LL pin6 Phase switch Ringing max=23.9V；VBST-LL(pin4/pin6) max=5.85V，min=250mV。

    

    

2）I see SLUA831A document，add Rs+Cs，Rs=1ohm，Cs=470pF; VBST-LL(pin4/pin6) max=7.20V，min=-900mV ; exceed the standard.(at 16A load).

   

3）I try Rs=0ohm~5ohm range，Cs=100pF~3.3nF range.The smaller the Cs, the lower the voltage VBST-LL.

so，my question：

1）VBST-LL Is there any risk beyond the range of -0.3~7V？

2）Cbst，Rs，Cs debug range？

3）LL Phase switch Ringing Does it affect the stability of the power loop，dynamic load？

4）Does the oscilloscope need to set bandwidth restrictions？

Thanks.

  • 0
    TI__Expert 3280 points

    Hello,

    Let me check and get back to you.

    -Hitesh

  • 0 in reply to Hitesh Chandwani
    TI__Expert 3280 points

    Hello,

    1. Yes you should not cross the datasheet absolute max limits else it may not work as per the specs mentioned in the datasheet and even may get damaged.

    2. refer SSZTBC7 Technical article | TI.com

    3. Yes, it may affect.

    4. 500 MHz is sufficient.

    you can check your layout and also try to reduce the Switching node ringing which will help reducing the BST-LL ringing.

    -Hitesh

  • 0 in reply to Hitesh Chandwani
    Prodigy 120 points

    Hi Hitesh:

        1）Rs，Cs range？any value is ok？

        2）SLUA831A Is the document incorrect? “refer SSZTBC7 Technical article | TI.com” What's the difference with this?

        3）Cbst value can debug change？0.1uF?0.22uF?etc....

        4）Rbst=5.1 ohm，Cbst=0.1uF， BST-LL ringing range is ok. but Switching node  have ringing，Can we not increase Rs, Cs？

        5）VBST-LL range spec is DC value，Can we accept ~ns pulses, similar to LL？

           

    Thanks

  • 0 in reply to user6304695
    TI__Expert 3280 points

    Hello,

    1. generally you can keep Rs in 1 - 20 ohms and calculate capacitor accordingly which will be in some pF

    2. yes you can refer to SLUA831A also, its similar

    3. bootstrap cap should be 0.1uF only, as it is designed according to internal mosfets capacitors.

    4. increasing RBST may decrease the efficiency, so better to tune Rs and Cs to decrease the ringing.

    5. No VBST-LL should not go above the absolute ratings, solving the switch note ringing will reduce this voltage.

    -Hitesh