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TPS799: How to adjust start-up time of TPS799

Part Number: TPS799

Hello team,

I have some questions about start-up time of TPS799.

In the datasheet, 6.5 Electrical Characteristics, Start-up time is described as Typ 50us (CNR=NONE). Are there Max and Min values too?

Also, Is there a way to calculate or adjust start-up time? Since the customer's clock source has rise time of 36us or more, they want to adjust, and have more margin in their design.

Best Regards,

Ryotaro Fukui

  • Hello,

             This is a parameter that is usually not tested at production and would also vary depending on the values of the capacitors selected, and hence we do not have the Max and Min values for this. The value of the current source that charges the noise reduction capacitor is not known to us at this time, hence we do not have a way to calculate the start-up time. Typically the start-up time can be increased by increasing the value of input cap, output cap and/or the noise reduction cap. Increasing the Input/output caps will however increase the inrush current and this could lead to the part hitting current limit and/or thermal shutdown. Thanks!

    Regards,

    Srikanth

  • Hello,

    Thank you for the response.

    I understand that the start-up time varies with capacitors and current sources.

    Could you be able to calculate the start-up time if I shared their usage condition? If so, I would like to share their circuit diagram through email of internal thread.

    Regards,

    Ryotaro Fukui

  • Hello,

             I am looking into this, I will get back to you by the end of Monday next week (12/06).

    Regards,

    Srikanth

  • Hello,

             This device incorporates a quick start mechanism. Hence, if an output capacitor close to the typical value is selected, the start-up time cannot vary much from ~50uSec even for a wide range of NR/SS cap values. My earlier response seemed to suggest that the start-up time for this device is adjustable, however this is not the case because it incorporates quick start. I apologize for the confusion.  

    Regards,

    Srikanth    

  • Hello,

    Thank you for the correction.

    I understand that this device has start-up time fixed. I am going to decided whether to continue using this device or another start-up time variable device.

    Thank you for your support.

    Best Regards,

    Ryotaro Fukui