• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 48 subscribers
  • Views 658 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.

LMC660: We are looking to replace LMC660 low bias current opamp with a new opamp.

Ray Vincent Aranzaso
Genius 16065 points
Part Number: LMC660
Other Parts Discussed in Thread: OPA4344, LMC6036, LMP2234, LMP7709, LMP7704, OPA391, OPA4345, OPA396, TLV9104, OPA392, LMV831, OPA314, OPA313

Hi,

Good Day. I have a customer who has a query about LMC660. Please see below his query for your reference. Thank you very much.

We are looking to replace LMC660 low bias current opamp with a new opamp.

We need to make sure the bias current is as low as the LMC660. Do you have any recommendations?

We have been using the LMC660 for a long time and in one of our applications we have been using it to measure currents down to a few pA. We need a replacement in a smaller package but that still has low bias current. Supply voltage is ~5V.

Best Regards,

Ray Vincent

  • 0
    Guru 140200 points

    Hi Ray,

    smaller package?

    LMC6036, OPA4344, LMP2234, LMP7704, LMP7709 all come in TSSOP package.

    Kai

  • 0
    TI__Genius 10716 points

    Hello Ray,

     

    I agree with Kai's suggestion of devices.

    The specifications for a quad channel amplifier with sub 2 pA max input bias current may limit the options considerably.( Link Here )

    I have included a device comparison table below for some of the possible device alternatives

    Are there any other parameters that must be met for the application?

    Both mentioned options (OPA4344 LMC6036) offer sub 2 pA ib max in a TSSOP or SOIC package, however some performance specifications will be worse in comparison to the LMC660.

    If the reduced Isc capability and higher noise of the OPA4344 or LMC6036 can be tolerated, both could be suitable alternatives depending on further system requirements.

    Note, more recently released devices will likely meet or exceed most specifications of the LMC660, however will still possess around 10-15 pA ib max.

    Please let me know if you have any further questions.

    Regards,

    Jacob

  • 0 in reply to Jacob Nogaj
    TI__Genius 16065 points

    Hi Jacob,

    Good Day. Please see the latest response of our customer to your reply. Thank you very much.

    Hi thank you for your recommendations. Apologies I should have mentioned we are going to use single opamps in SC-70 package. We have looked at OPA391, OPA392 and OPA396 and they have very low input bias current, but have not tested them as out prototype boards at the moment used SOIC14 LMC660. The design works well with LMC660 with 5V supply. When we replaced the LMC660 with OPA4345 the circuit becomes very unstable, we are still investigating this but it may be due to us needing to drive an output with capacitance up to 4u7F, also noise rejection on the opamp does not seem very good. We are also ordering SOIC14 samples of TLV9104 (max 10pA bias may be ok). What opamp do you recommend that could replace LMC660 (only difference supply voltage will be between 5V-5.3V) in SC-70 package?

    Best Regards,

    Ray Vincent

  • 0 in reply to Ray Vincent Aranzaso
    Guru 140200 points

    Hi Ray,

    I think some changes have to be made in the circuit to be able to handle the huge capacitive load. Please post a schematic.

    Kai

  • 0 in reply to Ray Vincent Aranzaso
    TI__Genius 10716 points

    Hi Ray,

     

    Thanks for the clarification on some of the requirements.

     

    As Kai mentioned, a schematic would be very helpful. Being that a 4.7uF load capacitance is a substantial load to drive, it would be highly recommended to conduct stability tests on the design to ensure suitable phase margin.

     

    The OPA391, OPA392, and OPA396 are all precision amplifiers. I can always reassign the thread to the appropriate group if the customer has any questions regarding the application of these amplifiers

     

    For general purpose amplifiers, I would suggest looking at the OPA313, OPA314 and LMV831.

    The comparison table below includes some of the characteristics for the mentioned amplifiers.

    I can more accurately make device recommendations with a further understanding of the schematic and application. Additionally, all devices suggested above have a higher Ib max and Ios max compared to that of the LMC660.

    Here is the link to the search parameters I used to find general purpose amplifier devices in SC70 with sub 12pA Ib max. (Link Here)

    Please let me know if you have any questions.

    Thank you,

    Jacob