• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 47 subscribers
  • Views 246 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

PGA855: Stability versus output capacitance

Sariel Hodisan
Prodigy 145 points
Part Number: PGA855
Other Parts Discussed in Thread: PSPICE-FOR-TI, TINA-TI, ADS1115

Tool/software:

Hello,

I plan to use a filter at the output of the PGA855 as follows:

Riso= 2000 ohm

Differential capacitor: 1uF

Can the PGA855 withstand it and not oscillate? I hope the Riso is large enough.

Thanks

Sariel


  • +1
    TI__Mastermind 22312 points

    Hey Sariel, 

    Welcome to e2e! :) 

    I used the simulation models available in the product page to support this analysis. The PGA855 is available for evaluation in both TINA-TI and PSpice-for-TI - both are free to download. 

    As you can see with the 2k RISO, there is no sustained oscillations (or instability) but it takes a long time to ramp up and down. 

    The RISO can be reduced down to around 100ohm, there is no sustained oscillation and has a faster ramp up and down time. 

    Zoomed in version:

    PGA is in a gain of 4. Here is the simulation file I used: pga855_1uf.TSC

    Is there a reason you are using such a large capacitor? Could you point me in the direction of an ADC that requires it?

    All the best,
    Carolina

  • 0 in reply to Caro Walter
    Prodigy 145 points

    Thank you, Caro.
    This solves my issue and makes me a relaxed designer!

    I use such high RC at the outputs since I am going to use low sample rates and low BW. I will interface the PGA855 to ADS1115.

    Sariel,