ADA4627-1 and capacitive loads

Hello,

 

I want to use the ADA4627-1 as output buffer in unity-gain configuration in a DAC application. The op amp input is connected to an analog switch. Therefore high slew rates can arise at the input of the op amp. The resistive load connected to the op amp output is 10kOhm and the capacitive load is 2nF. Furthermore the application requires a slew rate >=10 V/µs. The analog input voltage is +-10V and the maximum supply voltage is +-14V? Do you think the ADA4627-1 is a good solution for this application or would you recommend another op?

 

Can you provide me information how the input voltage range of the ADA4627-1 scales with the supply voltage? The data sheet contains only information for a supply voltage of +-15V. As mentioned above, the max. supply voltage in my application is +-14V and I want to be sure that the analog input range of +-10V is within the input voltage range of the op amp.

 

Regards,

Steffen

  • 0
    •  Analog Employees 
    on Mar 3, 2013 7:55 PM

    Hi Steffen,

    Thank you for considering ADI amplifiers for your design. To determine the input voltage range (IVR) of an amplifier at a supply voltage (Vs) different from the test condition on the datasheet, we need to approximate the input headroom required by the amplifier. To do this, we subtract the specified IVR from its corresponding specified Vs. For the case of ADA4627-1 at room temperature, IVR=+/-11V for Vs=+/-15V. This yields an input headroom of +/-4V. Now to get the IVR at +/-14V supply, we subtract the headroom from the supply voltage. Therefore the IVR, at room temperature, is +/-10V for a supply of Vs=+/-14V. However, we take note that the IVR could vary as the operating temperature varies. As stated on the datasheet, for Tmin to Tmax, IVR=+/-10.5V at Vs=+/-15V. Thus, approximately IVR  is +/-9.5V at Vs=+/-14V from Tmin to Tmax. The calculations we made suggest that ADA4627-1 may not be the best part for your application.

    You may want to look at AD8510 which has an IVR=-13.5V,+13V for Vs=+/-15V, however with lower SR of 20V/us and phase margin of 55degrees compared to 40V/us and 72degrees respectively for ADA4627-1. If you're okay with duals, you may want to check on ADA4001-2 and AD826.

    In addition, since you are driving a capacitive load, you may want to read on OP AMPS DRIVING CAPACITIVE LOADS.

    I hope this helps.

    Best regards,

    Neil

  • Hi Neil,

     

    thank you for the explanation. Does the input headroom remain constant over the full supply range? The AD8510 datasheet is fully specified for +-5V and +-15V. It seems that the input headroom of the AD8510 increases with increasing supply voltage. Does this also hold for the ADA4627-1? If yes, can you give me a rough estimation about the input headroom for +-5V? Furthermore, I would be interested if the input headroom scales approximately linear with the supply voltage?

     

    Regards,

    Steffen

  • 0
    •  Analog Employees 
    on Mar 6, 2013 4:18 PM

    Hi Steffen,

    According to the designer, the ADA4627-1 headroom is approximately constant across the rated supply range.

    Please let me know if you have more questions.

    Cheers,

    Neil

  • 0
    •  Analog Employees 
    on Mar 7, 2013 6:06 PM

    Hi Steffen,

    In line with my recommended parts in my first reply, I found out that the newer ADA4610-2 (dual) could be a much better replacement. It is the direct next generation of AD8512 (dual version of AD8510) and at the same time better trimmed version of ADA4001-2. The single (ADA4510-1) and quad (ADA4510-4) versions are currently not yet out but they will become available soon though.

    Regards,

    Neil

  • Hi Neil,

    thank you for the information. Can you give a rough estimation when the ADA4610-1 will be available?

    Regards,

    Steffen