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TPS7A7001 Soft Start

BX27
Genius 3900 points
Other Parts Discussed in Thread: TPS7A7001

Hi there!

We use TPS7A7001 to provide 3.3V power. We found in our PCB, some TPS7A7001's Vout Rising time is about 500us, do not satisfy the load's requirement (＞1 ms).  While some other TPS7A7001 do have longer rising time which is larger than 1ms.

There is no Soft Start feature for this IC. We try to add RC filter on EN input, or increase the Cout to 20uF, but neither is effective. My questions are:

(1)Is there any way to increase Vout rising time? Or is there any pin-compatible IC that can replace TPS7A7001?

(2)For general, what will influence its Vout rising time ?

Following is SCH.

Thanks!

  • 0
    TI__Expert 3910 points

    Hi Yi Xiao,

    (1)Is there any way to increase Vout rising time? Or is there any pin-compatible IC that can replace TPS7A7001?
    I am not aware of a pin compatible part that has the Soft Start functionality, however, if there was any way you could add a Feed Foward Capacitor (a capacitor between the Output and Feeback, or pins 6 and 7) you can increase the rising time. 

    In such case your start-up time is divided into two stages that is: tstart-up = tref + tCFF.

    However, in most cases you can approximate your tstart-up to tCFF, where the tCFF charging time is determined by the resistance of R1 (R413 in your schematic) and the capacitance of CFF. In this case, your start-up time will be given by the equation: tstart-up ≈ tCFB = 3 * R1 * CFF 

    For more information feel free to take a look at section 2.1 of application note "Pros and Cons of Using a Feedforward Capacitor with a Low-Dropout Regulator (TI Document: SBVA042)".

    (2)For general, what will influence its Vout rising time ?
    Generally the factors that will influence the rising time of VOUT are the rising time of VIN, COUT and CFF.

    Best Regards,
    Victor

  • 0 in reply to Victor Salomon
    Genius 3900 points
    Thank you very much, Victor! Your suggestion works !!!