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TPS717: Check points for stability operation

Takashi Onawa
Genius 13200 points
Part Number: TPS717

Hi Team,

I have three questions about TPS717. Could you answer following questions?

1. Let me confirm if the Ifb value is typo or not.
The I_FB max is 1uA so it might introduce 0.32V offset by 320kohm FB divider…

2. Is it possible to use 10k to 100k resisters as FB voltage divider? 
Although i'm understanding the datasheet recommends to use 160k~320k register as R2, my customer want to use smaller value due to the leakage discussing above.

3. What frequency range should be met for ESR requirement for stable operation?  Also are there any min ESR requirements for stable operation? 

Datasheet requests to chose less than 1 ohm ESR cap for stability reason but ESR of cap fundamentally has variations depending on frequency. 
At low frequency range, almost cap tends to have 1 ohm or larger ESR.

Regards,

Takashi Onawa

  • 0
    TI__Guru 55940 points

    Hi Takashi,

    Correct, Ifb max is 1 uA.  This is a tested condition and not a typo.  As you state Ifb can introduce a voltage error; however, this is considered negligible when Ifb << Iout.

    TPS717 was designed, tested, and characterized for R2 to be within the 160 k to 320 k range.  While smaller resistors can be used, your application will be less efficient and may not meet all of the specifications as depicted in the datasheet.  We recommend building a prototype of your application to better understand what performance you can expect before committing to the lower resistor values.

    The ESR requirements for linear regulators should be met at the resonant frequency of the capacitor. This is the lowest point on the capacitor impedance curve.

    Very Respectfully,

    Ryan