INA821 datasheet(36/52 Pages) TI

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9.2.2.1 Design Requirements

The requirements for the application driving the ADS8900B ADC are listed in the following table.

Table 9-1. Design Parameters

PARAMETER

VALUE

Differential to differential conversion

VINDIFF to VOUTDIFF

Supply voltages

VS± = ± 15 V, VDD = 5.2 V, VREF = 5 V

Full-scale range of ADC for FSR

FSR = ± 5 V

Driver configuration

See Table 9-2

Circuit bandwidth

f(–3dB) = 31.7 kHz

Output RC elements

See ADS8900B input requirements

To eliminate ground loops, unwanted parasitic effects, and distortion, use appropriate PCB layout and grounding

techniques (see also Section 9.4).

9.2.2.2 Application Curves

Table 9-2 show the typical signal-to-noise (SNR) and total harmonic distortion (THD) of the INA851 driving the

ADS8900B SAR ADC at full-scale range and at different gain configurations. The RC filter combination (RFIL,

CFIL) shown in Figure 9-6 helps attenuate the nonlinear charge kickback of the ADC and optimize for best

THD performance. The combination of the RC filter and the feedback capacitor CFB allow for the best trade-off

between harmonic distortion and maintaining stability of the FDA. Low voltage-coefficient C0G capacitors are

used everywhere in the signal path (CFB, CFIL) for the low-distortion properties.

For other bandwidth requirements, adjust the feedback capacitor accordingly, and verify the circuit performance

using a SPICE simulation using the INA851 TINA-TI™ SPICE Model. The amplifier output voltage must settle

within the ADC bit accuracy during the ADC acquisition time window. Verify the desired circuit is stable; that is,

the FDA has more than a 45º phase margin.

Table 9-2. INA851 + ADS8900B FFT Data Summary

INPUT AMPLITUDE

(Vpk)

RG RESISTOR (Ω)

GIN (V/V)

GOUT (V/V)

SNR (dB)

THD (dB)

ENOB (Bits)

23.7378

None

0.2

100.7

–117.3

16.42

4.7476

None

100.6

–122.7

16.41

0.2374

316

99.1

–112.0

16.10

0.0475

60.4

100

91.1

–99.0

14.64

G = 0.2 V/V, fIN = 1 kHz, SNR = 100.73 dB, THD = –117.28 dB

Figure 9-7. Noise Performance FFT Plots for

G = 0.2 V/V

G = 1 V/V, fIN = 1 kHz, SNR = 100.6 dB, THD = –122.74 dB

Figure 9-8. Noise Performance FFT Plots for

G = 1 V/V

INA851

SBOS999A – MARCH 2022 – REVISED OCTOBER 2022

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