• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 1 answer
  • Subscribers 49 subscribers
  • Views 1804 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

LM324: What is the the most Cload stable opamp that has the same footprint as the LM324

Relay Man
Prodigy 70 points
Part Number: LM324
Other Parts Discussed in Thread: LM8261, LM8272,

Hi,

I am looking for an opamp that is unity gain stable and can be used in v ref applications 2.5V 3.3V suppl, CL about 200nf.

Any suggestions? The DC load current is uA and constant.

Thanks

  • 0
    Guru 140200 points

    Hi,

    why not using the standard way to isolate capacitive loads?

    Kai

  • 0
    TI__Expert 6625 points

    Hi Relay,

                   I would recommend LM8261 and LM8272 for your application. They have unlimited capacitive load drive. I have outlined some quick specs below, for a thorough analysis please refer the datasheet: http://www.ti.com/lit/ds/symlink/lm8261.pdf 

    VccMin:

    2.5 V

    VccMax:

    30 V

    VinMin:

    -0.3 from V- rail

    VinMax:

    0.1 from V+ rail

    VoutMin:

    0.09 from V- rail

    VoutMax:

    -0.17 from V+ rail

    Offset voltage (Max):

    5 mV

    TcVos (Typ):

    2 uV/°C

    Bias current (25°C Max):

    2 uA

    Supply current (Max per Ch):

    1.25 mA (per channel)

    Output current:

    53 mA

    Open loop gain:

    95 dB

    Slew rate:

    12 V/us

    Bandwidth:

    21 MHz

    Voltage noise:

    15 nV/Sqrt(Hz)

    Current noise:

    1 pA/Sqrt(Hz)

    Differential gain:

    -- %

    Differential phase:

    -- Deg

    Best Regards,

    Bala Ravi

  • 0 in reply to Bala Ravi
    Guru 140200 points
    Hi Bala,

    yes, these OPAmps can drive an unlimited load capacitance. But you have to pay a high price for this. Figure 29 of datasheet of LM8261 shows an overshoot of up to 65%!

    Kai
  • 0 in reply to kai klaas69
    TI__Expert 6625 points
    Hi Kai,
    Thanks for your feedback. We don't have many amplifiers that can take in large CL. Between adding an Riso (Series Isolation Resistor) between the op-amp and cap can help with overshoot and settling time.

    Best Regards,
    Bala Ravi
  • 0 in reply to Bala Ravi
    Guru 140200 points
    Hi Bala,

    yes, the introduce of Riso can drastically improve the performance.

    Kai
  • 0 in reply to kai klaas69
    TI__Guru**** 152966 points
    Another concern is DC voltage range. The application request is "v ref applications 2.5V 3.3V suppl, CL about 200nf."
    I read that as a 3.3V supply and the Vref will be 2.5V. LM324 cannot source 2.5V with a 3.3V supply due to the NPN Darlington output stage. Adding a pull up resistor could solve this problem by making LM324 sink current like a shunt regulator only sinks current. The second problem is the input common mode range. 2.5V won't work with 3.3V power due to Darlington input stage. Having an input at 1.25V and setting gain to 2 could fix that problem. Stability can be improved by Kai’s 1st post.