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TPS628501-Q1: soft start feature

Chuqiang Wen
Expert 5160 points
Part Number: TPS628501-Q1
Other Parts Discussed in Thread: TPS62816-Q1,

Tool/software:

Hi Team, 

Customer measured the start-up waveform on both TPS628501-Q1 and TPS62816-Q1, show as below. TPS62816-Q1 and TPS628501-Q1 start up rising edge has some voltage steps which looks like the SS controlling the slew rate.

  1. Please provide more details about the internal network and help to improve the rising edge.
  2. Why it shows voltage step? Does it will impact the loop response? 
  3. For TPS628501-Q1, it is internal soft start. Any methods that we can optimize it from external circuitry? 

Customer hope they can get the rising edge more smoothly. 

TPS628501-Q1 output start up waveform: 

TPS62816-Q1 output start up waveform: 

Thanks!

Ethan Wen

  • 0
    TI__Genius 14810 points

    Hello Ethan,

     

    This step you can see in the datasheet plots also that it is normal: It is more visible at low current. During the startup, device is in PFM mode and also because of the low current also, output voltages charges faster and then it takes while for the VREF to reach at the same point as VFB. which causes this plateau.

    Do you think, it will be an issue for customer? Because device is stable.

    Customer can try to add more ouput capacitance that can help to smooth this but this is not the stability issue.

    Thanks,

    Farheen