47kW

47kW

10kW

Microphone,

Hydrophone

etc.

Thermocouple

Center-tap provides

bias current return.

INA129

INA129

INA129

INA129-EP

SBOS508 – DECEMBER 2009

www.ti.com

Figure 25. Providing an Input Common-Mode Current Path

Input Common-Mode Range

The linear input voltage range of the input circuitry of the INA129 is from approximately 1.4 V below the positive

supply voltage to 1.7 V above the negative supply. As a differential input voltage causes the output voltage

increase, however, the linear input range will be limited by the output voltage swing of amplifiers A1 and A2. So

the linear common-mode input range is related to the output voltage of the complete amplifier. This behavior also

depends on supply voltage (see Figure 5 and Figure 6).

Input-overload can produce an output voltage that appears normal. For example, if an input overload condition

drives both input amplifiers to their positive output swing limit, the difference voltage measured by the output

amplifier will be near zero. The output of A3 will be near 0 V even though both inputs are overloaded.

Low Voltage Operation

The INA129 can be operated on power supplies as low as ±2.25 V. Performance remains excellent with power

supplies ranging from ±2.25 V to ±18 V. Most parameters vary only slightly throughout this supply voltage range.

Operation at very low supply voltage requires careful attention to assure that the input voltages remain within

their linear range. Voltage swing requirements of internal nodes limit the input common-mode range with low

power supply voltage. Figure 5 and Figure 6 show the range of linear operation for ±15 V, ±5 V, and ±2.5 V

supplies.

12

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