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AOP

Category: Hardware
Product Number: LT6233
Software Version: No

Hello,

I would like to find a equivalent with this component 'LT6233CS6#TRMPBF' because i have to order 5000 pieces. Do you know any components with the same footprint and the same function pins because I have already designed the PCB.

Thank for your helps

Regards

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  • 0
    •  Analog Employees 
    •  Super User 
    in reply to 206_RC

    Hi ,

    Regarding the offset you're seeing from using LT6233 as a Sallen Key High Pass Filter:

    Most of that is due to the input bias current of LT6233 (3uA max) flowing through the 22.5kohm input resistor (R1).

    I've added a dummy current source to your schematic to allow you to change that current and see the output offset go away or increase (depending on the magnitude and direction of that current).

    Here is the simulation file:

    LT6233 Sallen Key Filter Offset EZ 7_11_22.asc

    To resolve this issue, you can do one or both of the following:

    1. Scale your R's lower and your C's higher (to maintain the same filter response) by the same factor (e.g. 22.5k ->2.25k and 1uF --> 10uF, etc.) to reduce the impact of input bias current on output shift.

    2. Switch to another Op Amp with CMOS / JFET input structure where the input bias current reduces to the pA range. Let me know if you need help selecting a usable device?

    Additionally, I added a shunt resistor to your 2nd stage (R3) to allow for input bias current flow.

    Regards,

    Hooman

  • Hi,

    Thank you for your helps (I had not seen this bias current). In fact my signal from the hydrophone ( is about 1µV to 300µV). And after your simulation that I modified to have 1µV at the input :

    I think it is impossible to satisfy the maximum variation and the minimum variation. In fact I don't know if I must amplify the signal before before attacking the high pass filter. But what is the minimum voltage level that AOP LT6233 can accept ?

    I think, the better solution is to have a component with with adjustable offset and very low bias current. I don't know if it exists.

    You add a dummy current source : -1.5µA 

         

    But how do we do it electronically ? Is there a dedicated component for this or a specific assembly ?

    But now, I see the problem more clearly thanks to your advice.

    Regards


     

       

  • Hi Hooman,

    Sorry to bother you but I'm still looking for a -1.5µA current source and haven't found it yet.

    Thank for your helps

    Regards

  • 0
    •  Analog Employees 
    •  Super User 
    in reply to 206_RC

    Hi ,

    Sorry to bother you but I'm still looking for a -1.5µA current source and haven't found it yet.

    Response: The -1.5uA current source I added was only there to demonstrate that the input bias current of LT6233 (about 1.5uA in its model) is responsible for your output offset. Once I added the -1.5uA current source, I was able to null the output offset. So, that's why I recommended choosing a device with CMOS / JFET inputs where the input current is in the pA or nA range (much lower) so that you won't have this offset.

    Regards,

    Hooman

  • I recommended choosing a device with CMOS / JFET inputs where the input current is in the pA or nA range

    Probably at the inputs of AOP, but how can I know if the inputs are CMOS/JFET ? In the datasheet ?

    After searching I found these selections :
    www.analog.com/.../11080

    There are 2 components that correspond to my selection : AD8233/AD8428

    The AD8233 with 'CHIPS OR DIE,20-Ball WLCSP (2.04mm x 1.705mm)' What is this box ? I just need boxes of types SOT-23 or equivalent.

    And for the second AD8428, you advised me in another Topic which I am trying to understand for the moment. 

    Thanks you for your helps

    Regard

  • 0
    •  Analog Employees 
    •  Super User 
    in reply to 206_RC

    Hi ,

    If you're looking for Instrumentation Amplifiers with low input bias current, you can look at this list sorted for the lowest noise voltage on-top, and input bias current < 400pA:

    www.analog.com/.../11080

    AD8233 that you mentioned is offered in WLCSP packaging or die only (not in SOT23). The closest packages to the SOT23 that you want which I can find is in 8-pin MSOP are:

    LT6370

    AD8220

    AD8428 is only offered in the 8-pin SOIC package.

    Regards,

    Hooman

  • AD8428 is only offered in the 8-pin SOIC package.

    Hi Hooman,

    For this package there is no problem for the manufacture and also MSOP. Sorry I don't know all package for cms components.  
    I'll see the LT 6370 and AD8220 and I will do the simulation with these components. Just one precision I use this AOP only for High pass filter not for Amplifier (or 1) 

    Thank you