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TPS7A16A-Q1: Question about soft-start current

NOBUO FUJIHARA
Genius 9005 points
Part Number: TPS7A16A-Q1
Other Parts Discussed in Thread: TPS7A16

Hi team,

My customer thinks to use TPS7A16A-Q1  48V to 12V regulator.

Load current is less than 10mA, but concerns about inrush current into output cap when device initially power-up.

This device has soft-start, can you provide more information how much current flow during soft start?

best regards,

  • 0
    TI__Mastermind 23361 points

    Hi Fujihara-san, 

    Yes, the TPS7A16 has a built-in soft start for in-rush control. Figure 16 will give you an idea of the slew rate of the output ramp. As you can see, the output roughly takes 400us to reach 5V and the slew rate can be estimated to be 12.5V/us. 

    For 12V output, it will probably take around 1ms to reach the target. 

    C = Q / V = txI / V, the in-rush due to the output capacitor can be estimated I = CxV / t

    Depending on the output capacitor used, the in-rush can be estimated by using the equation above plus the additional term contributed by the load.

    Regards, 

    Jason Song

  • 0 in reply to Jason Song
    TI__Genius 9005 points

    Hi Jason-san,

    Thanks a lot for your prompt support.

    I think 12.5V/us slew rate would not cause thermal issue with the customer's use case during start-up.

    May I confirm that slew-rate of Vout during soft-start is constant (12.5V/us) without regard to Vin and Vout level?

    Best regards,

  • 0 in reply to NOBUO FUJIHARA
    TI__Mastermind 23361 points

    Hi Fujihara-san, 

    For an LDO with a soft-start function, the slew rate is relatively controlled during the startup. But it may also experience variations from temperature and device-to-device. At similar conditions, for different Vin and Vout, you would expect a similar slew rate during soft-start. 

    Regards, 
    Jason Song