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TPS40200: Could you tell me how to calculate rising time of output voltage?

Kazuya Nakai59
Guru 20140 points
Part Number: TPS40200

 Hello guys,

 One of my customers is considering using TPS40200 for their next products.

 They have a few questions as the follows. Could you please tell me your reply?

 Q1. In Figure33 on page 25 of TPS40200 datasheet(SLUS659G), which range is correspond to tss calculated with equation (6) on page 17?

      Is the range from about 0.7V to about 1.4V? If the answer is yes, Figure 33 waveform has a little error from it. Do you know the reason of the error? 

 Q2. Do you have any equation which can calculate VOUT rising time (the time from voltage rising point to the target voltage stable point)?   

      In Figure 33, it seems that the rising time is about 800us.

 Your reply would be much appreciated,.

 Best regards,

 Kazuya.

  • 0
    TI__Expert 4720 points

    Hi Kazuya,

     Q1. I will double confirm with our expert about that.

    Q2. It should be like bellow:

  • 0 in reply to Neal Zhang
    Guru 20140 points

     Hi Neal,

     Thank you very much for your reply.

     About Q1,

     I see. I will wait for your next reply.

     About your reply to Q2,

     I know when VDD exceeds 8V, then Vsst is 8V. 

     I want to know  what Vsst voltage is in case of 5V VDD. Is it same voltage as VDD? Is it 5V?

     Could you give me your reply?

     Thank you and best regards,

     Kazuya Nakai.

     

     

  • 0 in reply to Kazuya Nakai59
    TI__Expert 4720 points

    Hi Kazuya,

    Yes you are right. VSST is the input voltage up to a maximum of 8 V. If input voltage is less than 8V, then VSST will be equal to input voltage.

    For Q1, the voltage difference is related to the inside of the IC and we need time to give you an accurate answer. For customer's application, I would say the soft start time will have variation. One reason is because of the 105 kOhm resistor. From EC table, the variation is big. 

    If you are still interested in the Q1 about 1.4V voltage accuracy, could you send me an email? (neal-zhang@ti.com). I will close the thread of E2E now. Thanks.

  • 0 in reply to Neal Zhang
    Guru 20140 points

     Hi Neal,

     Thank you very much for your reply.

     I understood that the soft start time had much variation because of your reply.

     But I still have a few questions about soft start time. So please let me ask you by off line.

     Thank you again and best regards,

     Kazuya.