THP210 datasheet(29/41 Pages) TI

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9.2.2 ADS891x With Single-Ended RC Filter Stage

The application circuit in Figure 9-12 shows the schematic of a complete reference driver circuit that generates a

full-scale range of 4.5 V at the ADC using a unipolar supply voltage of 5 V. This circuit is used to measure the

driving capability of the THP210 with the different variants of the ADS891x ADC.

To test the complete dynamic range of the circuit, the common-mode voltage VOCM of the input of the ADC is

established at a value of VREF / 2. To exclude distortion caused by reference voltage VREF and common-mode

voltage VOCM of the ADC, the test circuit uses the low-noise OPA2625 in an inverting gain configuration for V

OCM, and the high-precision, low-noise REF5050 for VREF. See the ADS8910BEVM-PDK user's guide for more

details.

AINN

AINP

ADS891x

VOCM = 2.25 V

THP210

+VS

VOD

R1 = 1k (0.1%)

R2 = 1k (0.1%)

R3 = 1k (0.1%)

R5 = 100 (1%)

C5 = 1 nF

C6 = 1 nF

R5 = 100 (1%)

R4 = 1k (0.1%)

C4 = 100 pF

C2 = 100 pF

VID

VREF = 4.5 V

+VS

5 V

+VS

Circuit driving capability:

ADS8910B at 800 kSPS

ADS8912B at 500 kSPS

ADS8914B at 250 kSPS

Figure 9-12. Driving ADS891x With Single-Ended RC Filter Stage

9.2.2.1 Design Requirements

The requirements for this application are:

• Differential to differential conversion

• Unipolar supply voltage of 5 V

• Full-scale range of ADC of FSR = ±4.5 V

• Input signal amplitude of VREF –0.4 dB

• Driver configuration in unity-gain buffer configuration (1-V/V gain)

• Circuit bandwidth f(–3dB) = 935 kHz

• Output RC elements set by SAR input requirements

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THP210

SBOS932B – FEBRUARY 2020 – REVISED OCTOBER 2020

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