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TPS54326 - rising-time of VIN (and VCC)

Dice-K
Mastermind 6330 points
Other Parts Discussed in Thread: TPS54326

Hello,
I am using TPS54326.
When a rising of VIN (and VCC) is slow, the output does not appear.
Is there a specification of a rising time of VIN (and VCC)?

Regards,
Daisuke

  • 0
    TI__Guru**** 191445 points

    There is no direct specification for it.  I probably know what your issue is, but would have to see waveforms and schematic to be sure.  There are timing and fault detection to consider.  If the device is enabled and teh VIN rise rate is slow, there may not be enough input voltage to allow the output voltage to be in regulation at the end of the slow start time.  After 1.7 x SS time, the UVP protection is active.  If the output is not in regulation, the UVP will latch the device off.  You will either have to increase the VIN rise time to meet that requirement or control the EN pin so that the device does not start up until the input voltage is sufficiently high.  let me know if this addresses your concern.

  • 0 in reply to JohnTucker
    Mastermind 6330 points

    Hello John,
    Thank you for your reply.

    If it is problem that VIN (and VCC) is slow, I increase the Soft-Start-Time.
    Now, the capacitor of Soft-Start-setting is 3.3nF. Soft-Start-Time is 1.26ms.

    Please teach me the upper limit of the Soft-Start-Time.

    Best regards,
    Daisuke

  • 0 in reply to Dice-K
    TI__Guru**** 191445 points

    I don't think there is a specific limitation.  Usually any SS time from 1 to 10 or 20 msec is safe to use with these parts.  You should be good to go with 1.26 msec.