• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 568 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS568215: soft start calculation with pre-biased load.

malli arjun1
Intellectual 610 points
Part Number: TPS568215

We are generating 5V@ 6A from 12V input.

The same 5V is diode OR ed with another battery source to power load when TP568215 is OFF.

Currently we used 47nF as the soft-start capacitor, as per equation 3 from datasheet, soft-start time is 4.7mS.

As we have diode OR with another low voltage source , when the TPS568215 enabled to generate 5V it will see pre-biased load, How the soft-start calculations will work with pre-biased load.

2nd question is, After enable reaches its turn ON threshold(1.225V), VREG5 starts and reaches its VREG5 UVLO - there is no data time taken in datasheet(figure 21) - Any data on approximate time to reach VREG5 UVLO after Enable crossed Turn ON threshold.

 

  • 0
    TI__Mastermind 18510 points

    Hi, when prebias start up, switching only begins after internal reference bigger than FB, then Vout begins ramp up, so you can think internal soft start time is same with no prebias.

    For Vreg5 start up time, it is related to the output capacitor value. Basically it is servers Hundreds us. Why do you want to know this? Let me double confirm it if you really need it.

    Yuchang

  • 0 in reply to Yuchang Zhang
    Intellectual 610 points

    " when pre-bias start up, switching only begins after internal reference bigger than FB" --> In our case(output voltage configured to 5V with 73.2K and 10K FB divider resisters) it means when Output voltage< 5V only switching starts. am i correct?

    we used Css as 47nF so, the soft-start time is 4.7mS, 

    lets say if output is pre-biased at 4V during soft-start, whether it takes same 4.7mS or (5-4)/4.7 = ~0.94mS to see output fully rises to 5V.

  • 0 in reply to malli arjun1
    TI__Mastermind 18510 points

    Yes, if Vout higher than 5V, not over OV, it will stop switching and also discharge function may be enabled, after internal reference get over the FB voltage, switching will begin again and Vout ramp up...

    if you use 47nf, For Vout, you just can see ~0.94ms(4V to 5V), but the switching begins at internal reference arrive 4V level.