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TPS22965-Q1: Can ON pin be connected to VIN directly?

Sherry Liang
Genius 10255 points
Part Number: TPS22965-Q1

Dear team,

My customer wants to connect ON pin to VIN pin directly without resistor, is it ok?

Thanks & Best Regards,

Sherry

  • 0
    TI__Genius 16085 points

    Hi Sherry,

     

    Thanks for reaching out on E2E!

    It is possible to connect the ON pin to VIN without a resistor between them, however there are some things to consider:

    - Rise time will be affected as VIN is changing. Shorting ON to VIN will affect the timing seen and the system will differ from the expected datasheet values.

    - EN cannot be left floating which is possible with a loss of Vin. If the device is powered and the ON pin is floating, we cannot confirm if the device is ON or OFF, meaning the device could also be partially ON. 

    As mentioned in the datasheet, we don't support ON floating. Therefore, we recommend a pull-down resistor from ON to GND to be used.

     

    Best Regards,

    Elizabeth

    If my reply answered your question, please click the "This resolved my issue" button. This can help others verify that a solution was found!

  • 0 in reply to Elizabeth Higgins
    TI__Genius 10255 points

    Hi Elizabeth,

    Thanks for your reply!

    1. I don't understand why rise time will be impacted if ON connects to VIN directly. Is there the power sequence requirement between these two pins?

    2. If ON, VIN and Vbias are connected together, ON pin won't be left floating under powered mode because they turn on/off at the same time. If the device is unpowered, it should be ok that ON is in floating status, right?

    Thanks & Best Regards,

    Sherry

  • 0 in reply to Sherry Liang
    TI__Genius 16085 points

    Hi Sherry,

    Allow me to clarify,

    1. For this device, the soft start timing (adjustable rise time) calculations in 9.3.1 of the datasheet are based off of a stable Vin rail. If the Vin rail were to be increasing, the soft start timing will behave differently than your expected timing result as the device references between the output and input voltage constantly shift. If the resultant timing performance is acceptable for your customer, then there shouldn’t be a problem.
    2. In this configuration, we’d be worried about the case where Vin is disconnected or powering down. Just because Vin is disconnected, it does not mean the voltage on the rail is 0V. This floating node could be anything (possibly between VIL and VIH). If there are capacitors on this rail, then the input will slowly discharge. In this configuration, you could have non-supported voltages for a noticeable time on Vin and ON. If there is no path to discharge the voltage on ON, we can’t say how long the voltage will be on this rail.

    Best Regards,

     

    Elizabeth