INA159 datasheet(21/51 Pages) TI2

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8.3.1.1 Gain Drift

The stability and temperature drift of the external gain setting resistor (RG ) also affects gain. The contribution of

RG to gain accuracy and drift is determined from Equation 1.

The best gain drift of 5 ppm/

℃ (maximum) is achieved when the INA819 uses G = 1 without RG connected. In

this case, gain drift is limited by the mismatch of the temperature coefficient of the integrated 40-kΩ resistors

in the differential amplifier (A3). At gains greater than 1, gain drift increases as a result of the individual drift

of the 25-kΩ resistors in the feedback of A1 and A2, relative to the drift of the external gain resistor (RG.)

The low temperature coefficient of the internal feedback resistors improves the overall temperature stability of

applications using gains greater than 1 V/V over alternate solutions.

Low resistor values required for high gain make wiring resistance an important consideration. Sockets add to

the wiring resistance and contribute additional gain error (such as a possible unstable gain error) at gains of

approximately 100 or greater. To maintain stability, avoid parasitic capacitance of more than a few picofarads at

RG connections. Careful matching of any parasitics on the RG pins maintains optimal CMRR over frequency; see

Figure 7-17.

8.3.2 EMI Rejection

Texas Instruments developed a method to accurately measure the immunity of an amplifier over a broad

frequency spectrum extending from 10 MHz to 6 GHz. This method uses an EMI rejection ratio (EMIRR) to

quantify the ability of the INA819 to reject EMI. The offset resulting from an input EMI signal is calculated using

Equation 2:

EMIRR (dB)

RF _ PEAK

100 mV

(2)

where

• VRF_PEAK is the peak amplitude of the input EMI signal.

Figure 8-2 and Figure 8-3 show the INA819 EMIRR graph for differential and common-mode EMI rejection

across this frequency range. Table 8-2 lists the EMIRR values for the INA819 at frequencies commonly

encountered in real-world applications. Applications listed in Table 8-2 are centered on or operated near the

frequency shown. Depending on the end-system requirements, additional EMI filters may be required near the

signal inputs of the system. Incorporating known good practices such as using short traces, low-pass filters, and

damping resistors combined with parallel and shielded signal routing may be required.

Frequency (Hz)

100

120

140

10M

100M

10G

D048

Figure 8-2. Common-Mode EMIRR Testing

Frequency (Hz)

100

10M

100M

10G

D047

Figure 8-3. Differential Mode EMIRR Testing

www.ti.com

INA819

SBOS959D – DECEMBER 2018 – REVISED APRIL 2022

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