• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 50 subscribers
  • Views 608 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.

Using DAC900 . Need Support for DAC900 output Driving Circuit

Amit Jagtap
Intellectual 510 points
Other Parts Discussed in Thread: DAC900, THS4281, LMH6321, THS4021, THS4221

Hi

I am Using DAC900 in my design. DAC Clock is 50MHz Max.  The output voltage required is  0 to 12V with 300mA maximum current.

The supply voltage available is +/- 12V. Kindly suggest proper Opamp to amplify and provide high current drive output of 12V using +/- 12 V opamp.

Because of Space constraint on Board I can't go for Boost regulator option and thus maximum supply available is +/- 12V only.  And thus need a Good Full Swing Rail to Rail opamp with GBW > 150MHz with supply voltage of +/-12V.

Regards

Amit PJagtap

  • 0
    TI__Genius 12965 points
    I've moved this to the high speed amplifier forum so that they can help with an amplifier recommendation.

    Ken.
  • 0 in reply to Ken C
    TI__Genius 12631 points
    Hello,
    Unfortunately we do not have an amplifier that can do full rail to rail while driving such a heavy load. The THS4281 is our best "true" rail to rail amplifier, however that doesn't have the current drive and the rail to rail performance is based on a 1K load rather than a 40Ohm load which is what you need.
    You will either need to boost the supplies or be prepared to live with diminished swing. Typically for such heavy loads you can expect to be around 2V from the rail.
    -Samir
  • 0 in reply to Samir Cherian
    Intellectual 510 points

    Hello,

    Currently I am using THS4021 in front of DAC900 with one current output terminated to ground with 50E. THS4021 o/p is given to LMH6321 to boost the drive current. Here I am using Boosted supply +/- 15V.

    Further I came to know that if from the differential current output, we are using only one output then we are loosing on Common mode noise reduction. Thus I wanted to replace current scheme with the new one in  which OPAMP will take differential current input from DAC and amplify that voltage to 12V with +/- 12V supply.


    If current = 300mA requirement is ignored, then pls confirm whether THS4281 is able to do this, and also comment on output current drive capability of THS4281.

    I just have a thought, Can it attained by BJT or MOSFET based design to drive high current and to provide full swing buffer.

    Amit

  • 0 in reply to Amit Jagtap
    TI__Genius 12631 points

    Amit,

      I looked at the THS4281 and unfortunately it doesnt have the signal GBW that you require. The THS4281 is only 40MHz. So it wouldnt meet your load current or BW requirement. It can swing to within 200mV of the positive rail, however that number is also based on the load the amplifier is driving. Please see attached datasheet for details (page 8):

    The THS4221 has a GBW of 125MHz, can drive 100mA of current and can also swing to within 300mV of the rail for a 500Ohm load. Note that all the amplifiers I mentioned cannot work on 24V total supplies. You can however run them with Vs+=12V and Vs-=GND. Of course this does mean that you will loose some swing on the negative rail as well. another option is to take multiple amplifiers and AC couple the outputs together to achieve the load current needs. Is this an option for you?

    -Samir

  • 0 in reply to Samir Cherian
    Intellectual 510 points

    I had a look in to datasheet of THS4281. Its not suitable my application.

    The THS4221 seems good choice.  Before that let me confirm on load resistance, Max drive current and output voltage tolerance.

    Meanwihle I will also simulate the performance of THS4221.

    As I noticed THS4221 is having GBW of 120 MHz and thus It will not give gain of 12 for frequencies I required. I need to use multiples gain stages with the same opamp.


    -Amit