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INA159: INA159

Neel Shah
Prodigy 60 points
Part Number: INA159


Below INA159 schematic snapshot and connection.

There are two options set for Vref between 0V to 2.5V by mounting R23 and R24 resistors.

I have query that in first option where R23 is mounted and R24 IS Do not populate. At that scenario 1 theoretically output voltage value is going to negative side but in simulation it is value around 1.96mV.

There is any ASIC design inside the opamp INA159 that will give as per below simulated values. Circuit also shown below for reference. At +IN pin applied voltage and -IN pin is grounded in both scenarios.

In second scenario theoretical and simulated value is perfectly matched. Could you please guide me on that why simulated value is different from calculated values? INA159 Simulated reading.xlsx

Applied Voltage
@ +IN,-IN (V)		 Voltage @ Vout Theoritical Vout(V) Applied Voltage
@ +IN,-IN		 Voltage @ Vout Theoritical Vout(V) 2.5
10 1.999997V 2 10 4.500011V 4.5  
2.5 499.989673mV 0.5 2.5 3.000003V 3  
1 199.98811mV 0.2 1 2.700001V 2.7  
0.2 39.989347mV 0.04 0.5 2.600001V 2.6  
0.1 19.993115mV 0.02 0.1 2.520003V 2.52  
-0.1 1.965223mV -0.02 -0.1 2.480001V 2.48  
-0.2 1.941491mV -0.04 -0.5 2.400002V 2.4  
-1 1.967217mV -0.2 -1 2.299999V 2.3  
-2.5 1.957365mV -0.5 -2.5 1.999997V 2  
-10 1.954625mV -2 -10 499.989673mV 0.5  
Table1 Table2 In Table 2 R23 DNP and R24 mounted.

  • 0
    TI__Mastermind 26475 points

    Hey Neel, 

    I am currently looking into this and will respond within 1 business day. 

    Best Regards, 

    Chris Featherstone

  • 0 in reply to Chris Featherstone
    Prodigy 60 points

    Hi Chris,

    Noted with thanks.

    Best Regards,

    Neel Shah

  • 0 in reply to Neel Shah
    TI__Mastermind 26475 points

    Neel,

    For the purposes of guiding the conversation I created a Tina ti simulation with a discrete ideal INA next to the INA159 both configured in the same way. The purpose of the discrete model is to understand what is happening internally when you apply the signals in your table. Can you confirm Scenario 1 and Scenario 2 are the way you are configuring your setup? I have attached the Tina Ti simulation file below. Tina Ti is available for free and can be found here: 

    https://www.ti.com/tool/TINA-TI

    The output will never get to the negative rail. There will always be some distance from either supply that the output voltage will reach. The output swing specification can be seen here:

    In my simulation the INA159 goes to 11.68 mV in scenario 1. This is expected because the amplifier internally sees 0V at it's inputs on a single sided supply and is attempting to drive it's output into the negative rail of zero. The output will be a Vds voltage above the negative supply and a Vds voltage below the positive supply. 

    Discrete INA.TSC

    Best Regards, 

    Chris Featherstone

  • 0 in reply to Chris Featherstone
    Prodigy 60 points

    Hi Chris,

    Thanks for the response.

    Your scenario 1 and scenario 2 is right, but I have simulated by using below model snapshot.

    I have simulated as per below through TI INA159 simulation model.

    Please refer below image for the same.

    Scenario 1

    Scenario2

    By changing input at opamp's noninverting terminal input voltage signal, We have prepared the excel sheet of those results.

    Below is snapshot.

    Scenario 1

    Scenario 2

    I understood that output voltage would not be go into negative side below the 0.010(10mV).

    But simulation is showing 1.957365mV. Is it right simulation value?

    My simulation readings are correct? Could you please check it because as per calculation is different and simulated values are different one. Which would be correct? Could you please cross check those value because it's output would be go into the single supply ADC inputs.

    Thanks in advance.

  • 0 in reply to Neel Shah
    TI__Mastermind 26475 points

    Hey Neel, 

    Thank you for confirming the circuits. I am looking into this and will respond within 1 business day. Thank you for your patience. 

    Best Regards, 

    Chris Featherstone

  • 0 in reply to Chris Featherstone
    Prodigy 60 points

    Hi Chris,

    Noted with thanks.

    Best Regards,

    Neel Shah

  • 0 in reply to Neel Shah
    TI__Mastermind 26475 points

    Hey Neel, 

    Let me know if I am misinterpreting your question. My understanding is that you are wondering if the model is correct and why the simulated values are not matching the theoretical values. 

    Running a DC sweep inside of Tina I get the same values that you do in simulation when using the configurations for scenario 1 and 2. For most devices the model represents the typical behavior based on typical parameter specifications listed within the product datasheet and are subject to vary within the min and max specified values.

    When using the circuit configuration conditions listed for the Vout measurement in the product datasheet the simulation is within specification.  The output is modeled between the min and typical specifications verifying the accuracy of this parameter. Below I see 11.6 mV.

    When altering the conditions you will get another value. The conditions you are simulating with are unloaded on the output from a DC perspective and this matches my expectations of being able to get closer to the supply rail. This behavior is observed in the output swing vs output current plot.

    The tina model and real measurements will differ from the perfect theoretical value. There will exist an input offset voltage on the input that gets translated to the output and other associated errors/limitations listed within the product datasheet table that will influence how accurately the real measurements are to the theoretical values. 

    Simulating with scenario 1 and 2 I see the same values listed within your table. 

    Ref1 = Ref2 = 0 V 

    Ref2 at 2.5 V

    I hope this provides some clarity on why you are observing values that differ from theoretical. 

    Best Regards, 

    Chris Featherstone

  • 0 in reply to Chris Featherstone
    Prodigy 60 points

    Hi Chris,

    Thanks for the sharing detailed data.

    My query is that can we consider the simulation data as a correct data?

    Another query is that what would be input voltage range for INA159 in below both scenarios? 

    Scenario1

    Scenario2

    In second scenario input voltage range is shown in datasheet as per below.

    What about for the scenario1 input range that is not shown in datasheet. Am I missing something?

    Thanks in advance.

  • 0 in reply to Neel Shah
    TI__Mastermind 26475 points

    Hi Neel, 

    Yes the model is outputting correct device behavior. The model represents the typical behavior based on typical parameter specifications listed within the product datasheet. When building the real circuit the real output values are subject to vary within the min and max specified values and on average you will observe the typical performance in the datasheet. 

    I am currently looking into your other questions and will respond within 1 business day. 

    Best Regards, 

    Chris Featherstone

  • 0 in reply to Chris Featherstone
    Prodigy 60 points

    Noted with thanks.

    Best Regards,

    Neel Shah

  • 0 in reply to Chris Featherstone
    Prodigy 60 points

    Hi Chris,

    Waiting for your response.

    Thanks in advance.

    Best Regards,

    Neel Shah

  • +1 in reply to Neel Shah
    TI__Mastermind 26475 points

    Hey Neel, 

    To check the input voltage range you can run a DC transfer characteristic analysis as shown below. 

    Running the DC transfer analysis I see that the input range is as shown in the plot below when both ref pins are tied to ground. 

    Best Regards, 

    Chris Featherstone

  • 0 in reply to Chris Featherstone
    Prodigy 60 points

    Hi Chris,

    Thanks for the quick response and guidance.

    Best Regards,

    Neel Shah