INA333 datasheet(21/49 Pages) TI2

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VOP

VON

100

VOP

VON

10 nF

PGA280

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SBOS487B – JUNE 2009 – REVISED MARCH 2020

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Feature Description (continued)

7.3.1.6 Output Stage

The output stage power is connected to the low-voltage supply (normally 3 V or 5 V) that is used by the

subsequent signal path of the system. This design prevents overloading of the low-voltage signal path.

The output signal is fully differential around a common-mode voltage (VOCM). The VOCM input pin is typically

connected to midsupply voltage to offer the widest signal amplitude range. VOCM is a high-impedance input that

requires an external connection to a voltage within the supply boundaries. The usable voltage range for the

VOCM input is specified in the Electrical Characteristics and must be observed.

The output stage can be set to a gain of 1 V/V and 1

⅜ V/V. THe output stage is set to 1 V/V after a device reset

or power-on, and is controlled by the gain multiplication factor.

Both signal outputs, VOP and VON, swing symmetrically around VOCM. The signal is represented as the voltage

between the two outputs and does not require an accurate VOCM. Therefore, the signal output does not include

ground noise or grounding errors. Noise or drift on VOCM is normally rejected by the common-mode rejection

capability of the subsequent signal stage.

The signal that passes through the output stage is internally monitored for two error conditions: clipping of the

signal to the supply rail and overcurrent. In fault conditions, an error flag bit is set (OUTerr).

7.3.1.7 Output Filter

The PGA280 uses chopper technology for excellent dc stability over temperature and life of operation. The

device is designed to avoid 1/f frequency (flicker) noise, and therefore enables both high resolution and high

repeatability for dc measurements. While the chopper noise components are internally filtered, a minimal residual

amount of high-frequency switching noise appears at the signal outputs. An external, passive, low-pass filter after

the output stage is recommended to remove this switching noise; Figure 48 shows two examples. This filter can

also be used to isolate or decouple the charge switching pulses of an A/D converter input.

Figure 48. Typical Examples of Recommended Output Filters

7.3.1.8 Single-Ended Output

The output stage of PGA280 is designed for highest precision. The fully-differential output avoids grounding

errors and noise, and delivers twice the signal amplitude compared to single-ended signals. However, if desired,

the output can be taken single-ended from one of the output pins referred to the voltage at the VOCM pin. The

output stage errors now relate to half the signal amplitude and half the signal gain. The unused output is

unconnected, but not disconnected from error detection. The usable voltage range for the VOCM input is

specified in the Electrical Characteristics and must be observed: the output swing (of both outputs) should not

saturate to the supply. Separate specifications for offset voltage and drift indicate higher offset voltage at lower

gains, because some error sources are not cancelled in the output stage connected in single-ended mode. Note

that the gain is one-half of the gain set in reference to the gain table (see Table 2).

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