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TPS7A25: TPS7A25

SS_hwdesign
Prodigy 250 points
Part Number: TPS7A25

Hi

I want to use TPS7A25 for one of my design.

My application requirement is for adjustable voltage output.( Vout = 4V).

I am refering datasheet : SBVS372A –DECEMBER 2018–REVISED MARCH 2019

My question is :

While refering Section 6.5 Electrical Characteristics, which mentions :

specified at TJ = –40°C to + 125°C, VIN = VOUT(nom) + 0.5 V or VIN = 2.4 V (whichever is greater), FB tied to OUT

>> As per my understanding [ VIN = VOUT(nom) + 0.5 V ] this will be applicable to only FIXED OUTPUT type design.

     am I correct?

>> As per the formula for adjustable Vout, 

     VOUT = VFB × (1 + R1 / R2)

     In this formula Vout is not at all dependent on Vin.

    So do I have to bother about [ VIN = VOUT(nom) + 0.5 V ] condition.

>> For Vout = 4V using adjustable output type configuration, is it possible to provide any VIN within specified VIN range i.e. 2.4V (min) to 18V (max)?

Thanks for reading.

  • 0
    TI__Guru 55940 points

    Hi ,

    The general test condition which you mention is to ensure that the TPS7A25 is regulating the output during testing.  Please note that our maximum dropout specification for TPS7A25 at the full 300 mA rated load is 340 mV.  As such, in order to achieve a regulated output at 300 mA, you would require a minimum input voltage of your 340 mV above your output voltage.  Therefore for a 4 V output, your minimum Vin for a regulated output is 4.34 V.

    You can learn more about dropout in our LDO Basics E-Book:

    http://www.ti.com/lit/ml/slyy151a/slyy151a.pdf 

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Prodigy 250 points

    Hi Ryan,

    Thank you for the reply. I got clarified my query on this topic.

    I have one more question regarding Cout.

    As per Recommended Operating Conditions, Cout can be from 1uF to 100uF with 2.2uF typ. value.

    How to decide the exact capacitance required?

    I have idea about Cout capacitance requirement varies with load transients and effect of bias voltage on capacitance.

    Thanks.

  • 0 in reply to SS_hwdesign
    TI__Guru 55940 points

    Hi ,

    The output capacitor selection will be driven by your specific application requirements.  Higher capacitance will decrease the magnitude of a transient response; however, the duration of the transient response will increase.  Additionally factors that can influence what capacitor(s) are used in a specific application are BOM cost and board space.  We highly recommend prototyping your application in order to determine what capacitor(s) will yield your desired performance.

    Very Respectfully,

    Ryan