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TPS54160A: Connect a capacitor to the EN pin

Kaji@PAN
Mastermind 7155 points
Part Number: TPS54160A
Other Parts Discussed in Thread: TLV841

Hello,

I am an FAE for a distributor that handles TI products.
I received the following question from a customer about the TPS54160A.
(Question)
I want the EN pin to ramp up slowly.
Is it okay to connect a capacitor to the EN pin?
It is planned to delay several hundred milliseconds by connecting a capacitor.
Since the SS/TR settings can only delay a few milliseconds, I'm considering starting up the EN pin slowly.
Also, if it is possible to connect a capacitor, is there a limit to the capacitor capacity?

Best regards,

  • 0
    TI__Genius 10665 points

    Hello,

    Using a 470nF capacitor connected to the SS pin will result in 150ms soft start time. If this is not acceptable for the customer then it may be possible to connect capacitor to EN as long as a resistor divider is included, and the capacitor is placed in parallel with the bottom resistor of the divider. 

    According to the datasheet: 'Do not place a capacitor directly on the EN pin if VEN > 5 V when using a voltage divider to adjust the start and stop voltage.' 

    Alternatively, a reset IC such as the TLV841 could be used to delay the start up time.

    Regards,

    Harrison 

  • 0 in reply to Harrison Overturf
    Mastermind 7155 points

    Thank you for your reply.

    My customer used a resistor divider and tested with a capacitor across the bottom resistor.
    However, the use of voltage dividing resistors has many limitations and cannot set a long time to delay the enable. . .
    (Question)
    Are voltage divider resistors absolutely necessary?
    What is the problem if I connect only a capacitor to the EN pin?

    Best regards,

  • +1 in reply to Kaji@PAN
    TI__Genius 10665 points

    Hello,

    Beyond what I stated previously there is no explicit language in the datasheet which prohibits the use of a capacitor placed directly on the EN pin. The resistor divider is necessary if you choose to adjust the input UVLO level, however the EN pin can be left floating and still start up on its own. Section 8.3.9 details the limits of the EN pin such as ensuring that the node voltage does not exceed 5V (as per the absolute maximum ratings table). One problem that I see is that the EN capacitor will need to be discharged when the device is turned off to ensure that consistent startup time can be achieved for subsequent startup sequences. Ultimately the customer will need to verify that this method implements consistent startup behavior.  

    Regards,

    Harrison