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INA133: Common mode voltage clarification, design help

ArTzy
Genius 13959 points
Part Number: INA133
Other Parts Discussed in Thread: INA148, INA149, , INA146

Hi Experts,

Seeking your assistance on this:

In one of our project we are using INA133U  as a dfifference amplifier with single supply of 15V and Vref (pin1) voltage of 7.5V . The sense (pin 5) is shorted with output (Pin6).  Can you please let us know the maximum and minimum common mode voltage input can be applied.

Suppose  we want to change over to INA149  or INA148  due to higher common mode input voltage. Can you provide us relation between common mode voltage, single  Supply voltage  and reference voltage. This help us to calculate the  maximum common voltage that  opamp can handle when operating with a given single supply.

Thank you.

Rgards,
Archie A.

PS:
I found this usual FAQ
[FAQ] Common Mode Voltage Range vs. Input Voltage Range...

Would like to clarify, if working with opAmp (not comparator):
The input is still valid even if one of the input signals is beyond/outside Vrail/input specified limit, as long as their common mode voltage is within its range, correct?

  • +1
    TI__Guru 60570 points

    Archie,

    According to the simulation for 15V single supply and Vref of 7.5V, INA133 TYPICAL linear input common-mode voltage range is from -4.5V to 21V - see below.

     However, the minimum input common-mode voltage, Vcm, is 3V from either rail, which means directly at the Vin it is half of 3V or 1.5V from either rail - see below.

    This means that on 15V single supply with Vref=7.5V, the minimum input common-mode voltage range is from -4.5V to 19.5V. 

  • 0 in reply to Marek Lis
    TI__Genius 13959 points

    Hello Marek,

    Thanks for the illustrations.

    We need clarification on the datasheet sheet values of common mode voltage. It states that positive CMV =(2*V)-3 and negative CMV = (-2V)+3. We understood that If supply voltage is +15V and common mode voltage will be (2*15)-3 ie 27. Please clarify. Can you provide us with Equations to derive the common voltage with different supply voltage ( for Both single and dual)supplies) and reference voltage?

    In our application we need to measure a signal with common mode voltage of 32V and single supply of +15 V. Can you please suggest a suitable IC or any other solution for this application?

    Regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Guru 60570 points

    Archie,

    If you look at the conditions specified for INA133 input common-mode voltage, Vcm, you will see that on dual supply +/-15V and Vref=0, Vin "sees" half of the Vcm voltage and therefore  -13.5V<Vin<+13.5V - this means that the VIN must stay 1.5V within both rails. 

    This results in the range -4.5V<Vcm<19.5V for Vref=7.5V on 15V single supply (1.5V<Vin<13.5) - see below.

    There is no way for INA133 accommodate Vcm=32V on 15V single supply. You do not say what is the minimum Vcm, thus, I will only consider upper range of 32V.  One way to cover Vcm of 32V would be to use Vcc of 18V and Vref=1V (see below min Vout swing).

    INA148 and INA149 would work just fine with fixed gain of 1 while INA146 has adjustable gain from 0.1 to 100.

  • 0 in reply to Marek Lis
    TI__Genius 13959 points

    Hello Marek,

    Thanks for your support and apologize for the delay in my response.

    We have now decided to work with supply voltage of 25 Volts and reference voltage of 6Volts. The common mode steady state voltage of minimum +15 volts and maximum of + 26.4 VDC.on which a sinusoidal wave of peak to peak value 21.18V(ie ( (125+16.2)*0.075A) will ride over and below the common mode voltage. We understand that input voltage (including cm voltage ) that can be applied to input terminals is ((2*25)-3= 47 V) under these conditions.

    Please let us know if this a reliable operating conditions for our application in the temperature range of -40 to 85Deg C. We eagerly await your response.

    Thanks and regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Guru 60570 points

    Archie,

    If you use Vref=0V on 25V single supply, you would be correct that the INA133 upper input common mode voltage, Vcm, range would be 47V since Vin must be 1.5V from either rail  - see below.

    However, with Vref of 6V allowable Vcm input range changes and is from -3V to 41V (Vin is at least 1.5V from either rail) - see below.

    I am not sure if I understand your conditions correctly but if the sinusoidal peak-to-peak signal is 21.2V riding on top of Vcm, it would imply +/-10.6V above and below Vcm. Thus, the overall range of input signal could be from 4.6V (15V-10.6V) to 37V (26.4V+10.6V), which is within allowable -3V to 41V range.

    Considering INA133 max offset of +/-450uV, drift 5uV/C and min CMRR 80dB, with INA133 gain of 1 they would NOT change the above input range.