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TPS54318: Power Sequencing

Srikanth Kacchu1
Expert 1185 points
Part Number: TPS54318

Hi Team

We are using TPS54318 in our design. Please clarify below.

1. Refer Image attached. Why pull up resistor is not placed at PWRGD pin when connected to enable pin of subsequent regulator.

2. Refer Image attached. I placed 100K external resistor between PWRGD and EN of subsequent regulator. My requirement is 2nd device should be disabled until 1st output is generated. What will be state of 2nd device EN pin until 1st output voltage is generated?

3. How to keep the 2nd device disable until 1st output voltage is generated?

Regards

Srikanth Kacchu

  • 0
    TI__Expert 7585 points

    Hi Srikanth,

    Thank you for your questions.

    1. The additional pull up is not needed since the EN pin has already an internal current generator.

     

    As clarified in the datasheet, if the EN pin is floating the device is automatically EN, therefore you don't need the additional pull up.

    2. I wouldn't advise to put the additional resistor, because it is not needed and it would cause an additional voltage drop on EN pin when the PWRGD pin is low (the current from EN pin will flow in the PWRGD pin through the resistor, causing a voltage drop). 

    3. The solution proposed in the datasheet is fine.

    At startup you have VOUT1 not yet regulated, PWRGD1 low and therefore also EN2 is low. The second device is disabled.

     After startup you have VOUT1 regulated, PWRGD1 floating and EN2 floating, therefore the device would be enabled. 

    Please ask again if you need further support.

    Thanks,

    Stefano

    All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).

  • 0 in reply to Stefano Panaro
    Expert 1185 points

    Hi Stefano

    Thanks for the quick support.

    Regards

    Srikanth Kacchu