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.

INA148UA - maximum common mode voltage curve on inputs with single supply

Other Parts Discussed in Thread: INA148, INA149, TINA-TI

Hi!

We use the INA148 (differential amplifier with high common mode voltage), on a aeronautical equipment, to receive a differential signal from A/C (Air Craft).

The context gives us voltage withstand constraints and our INA148 is supplied under 10V single mode. The datasheet gives the maximum common mode voltage admissible for 5V->15V symmetrical supply but only 5V for single supply, all at 25°C. Specific parameter are given with an offset of Vs/2 and Vs=5V : CMVR=[-47.5V;+32.5V].

It would be more practical to get a complete graph of the maximum common mode voltages according to supply voltage levels, offset levels and also a temperature coefficient. 

Anyway, do someone can tell me what are these maximums [-60 V;+55 V]?

Thank you

  • Hello Thomas,

    I agree that such a graph would help customers better understand the constraints of the device. As a matter of fact, such a graph is included in the INA149, which is our most recent difference amplifier.

    With respect to the INA148, the device's common-mode range depends on the resistor divider network and the common-mode range of the internal amplifier. I have built a TINA-TI model using discrete resistors and an op amp (attached). This allows us to understand the allowable voltages at the input pins of the internal op amp (not to be confused with the voltages at the pins of the device).

    /cfs-file/__key/communityserver-discussions-components-files/14/INA148cm.TSC

    After running a few simulations, I found that the positive common-mode voltage for the device should not generate a voltage closer to the positive supply than 1V. For example, given a single 5V supply (and Vref=0V), a common-mode voltage of 75V yields a voltage at the input pins of the internal amplifier of ~4V. Increasing the common-mode voltage will push this voltage closer to the rail and yield non-linear operation.

    For negative common-mode voltages, ensure that the voltage at the input pins of the internal amplifier do not go beyond the power supply voltage. In other words, the common-mode range of the internal amplifier is approximately (V-)<Vcm-int_op_amp<(V+)-1V. In order for the device to have a negative common-mode voltage while operated with a single supply, a reference voltage must be supplied (as shown in the Vs=+5V table).

    Finally, for your situation (-60V<Vcm-device<55V) with a single 10V supply, you must also supply a reference voltage of approximately 3.16V or greater in order to meet the negative common-mode value of -60V. This configuration easily accommodates the positive common-mode value of 55V.