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LMP7704: Signal Conditioning with limited Vref

JDJ
Expert 4486 points
Part Number: LMP7704
Other Parts Discussed in Thread: INA159

I am working on an op amp configuration that will have a +/-5V input and should output 0-5V to go into a 12 bit sar adc. I only have 5V and 3.3V available. Is there a way to make this work with a single op amp? I have attached my current configuration that has 2 op amps.

Also I am trying to maximize my acquisition time and even though there is a non-inverting gain, I want my bandwidth to be maximized. Can I limit the input bandwidth to help with a capacitor in parallel of the feedback? If so how do I select a capacitor value? 

Please let me know if you have any input or there are any relevant application notes/ white papers. 

+-5V with small vref.TSC

  • 0
    TI__Expert 4486 points

    I have decided to have a 4.5 output instead of my 5V output to avoid the additional bandwidth limitations and having a limited vref. I have attached the Tina file as well. 

    Thanks,
    Jack+-5V to 5V Final.TSC

  • 0
    TI__Guru* 93105 points

    Hi Jack,

    Have a look at the INA159 - a Precision Gain of 0.2 Level Translation DIFFERENCE AMPLIFIER. It was designed to accommodate a (+/-) bipolar input voltage and convert it to a unipolar output voltage. It is usable with a single supply from +1.8 to +5.5 V and can be configured in various ways to obtain different unipolar output voltage ranges. The resistors internal to the INA159 are precision resistors eliminating the need for external precision resistors. The datasheet goes over different gain configurations and what they are capable of providing. You can find the datasheet here:

    https://www.ti.com/lit/ds/symlink/ina159.pdf

    Keep in mind that no rail-to-rail output op amp swings to exactly 0 V. The on resistance of the op amp's output transistors is not zero and thus a voltage will be sustained across the output transistor to ground. Also, when an output is slammed into its maximum swing limits it is not longer operating within its linear operating regions and that should be avoided. The input range of the ADC should be set to accommodate the op amp's linear output range.

    Regards, Thomas

    Precision Amplifiers Applications Engineering