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TPS735: adjust the delay time of output

Intellectual 440 points

Replies: 4

Views: 75

Part Number: TPS735

Hello team,

I use TPS73501DRVR in my design, I want  to the output delay when power on,the delay time is 20~30ms.

The input power is 5V, the output  is 3.3V,I add the RC on the EN of TPS73501DRVR ,R=100k, C=1uF.

Since the VEN(HI)=1.2V, The delay time is calculated as follows:

delay time=ln(5/3.8)*100k*1uF=27.44ms.

Is the delay time calculation formula correct when power on?

Is there any other delay time need to add when power on?

Could you help to review the SCH as attachment, please give your comments,

Thank you.

kevin

sch_tps73501.pdf

  • Hi Kevin,

    This would not be reliable as the 1.2V threshold is the minimum in which we guarantee that the device will be enabled. The datasheet shows the following:

    So above, 1.2V, we say it will definitely be ON, and below 0.4V it is definiely OFF. Betwen these two thresholds, it could be in either state. 

    Using a device like the TPS3840 would be a way to precisely control the enable delay timing. 

    Does this answer your question?

    John Cummings 蔣康明
    Texas Instruments 德洲儀器
    Johncummings@ti.com

    Please click the "Resolved" link at the bottom of this post if I have answered your question.

    Thank you,

  • In reply to JCHK:

    Hi John,

    Thank you for your support.

    I will add precisely control the enable delay timing in my design.

    I want to know the delay time from EN(>1.2) to the output rise up to 3.3V, I can't find the delay time on the datasheet?

    Could you help to calculate this delay time ?Please refer to the  SCH.

    Which factors will affect this delay time?Is the delay time stable when I power on and power off repeately?

    Thank  you.

    Kevin

  • In reply to kevin p:

    Hi Kevin,

    We do not test this in production, but we do show a typical rise tine from EN going high to VOUT being in regualtion:

    so you are lookng at ~60us from Enable going high. This chart also highlight how the quickstart circuit help to maintain the statup time with different output capacitors. 

    Does this answer your question?

    Regards,

    John Cummings 蔣康明
    Texas Instruments 德洲儀器
    Johncummings@ti.com

    Please click the "Resolved" link at the bottom of this post if I have answered your question.

    Thank you,

  • In reply to JCHK:

    Hi John,

    Thank you for your support.

    Kevin

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