THP210 datasheet(31/45 Pages) TI2

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9.2.3 Attenuation Configuration Drives the ADS8912B

Many applications require to level-shift high-voltage input signals down to the lower-voltage ADC domain. Figure

9-16 shows an example of the THP210 used to attenuate a ±10-V differential signal to drive a differential SAR

ADC with full-scale range of ±4.5V. The common-mode voltage is shifted to the center of the ADC input range.

A multiple-feedback (MFB) configuration as described in Section 9.2.1 is used to provide a Butterworth filter

response, giving a 40-dB/decade roll-off with a –3-dB frequency of 100 kHz. The THP210 is powered with a 5-V

supply and a –0.232-V negative supply generated by the low-noise negative bias generator (LM7705) allowing

additional headroom for output swing to GND with ultra-low distortion. Alternatively, the THP210 can be powered

using a unipolar 5-V supply with good distortion performance.

The circuit is able to drive the ADS8912B 18-Bit SAR ADC at full throughput of 500-kSPS.

Fs= 500 kSPS

VOCM = 2.25 V

R1 = 2.1NŸ

R2 = 909Ÿ

R3 = 2.1NŸ

R6 = 909Ÿ

+ +

C4 = 470p

C3 = 470pF

C1 = 1.1nF

R4 = 2.74NŸ

R5 = 2.74NŸ

R8 = 100Ÿ

R7 = 100Ÿ

C2 = 1uF

C5 = 1nF

C6 = 1nF

THP210

í VID/2

+VCM

COG Ceramic Capacitors

0.1% Resistors

VS+

+5 V

VSí

í 0.232 V

+ VID/2

VS+

VSí

AINN

AINP

ADS8912B

VREF = 4.5 V

+VS

Figure 9-16. Driving ADS8912B in Attenuation Configuration of 0.4333 V/V

9.2.3.1 Design Requirements

The requirements for this application are:

• Differential to differential conversion

• Second order Butterworth filter with corner frequency of 100 kHz, offering flat frequency response

• Circuit accepts fully differential input signal of Vdiff = ± 10 V

• Circuit Attenuation is set to 0.433 V/V (–7.273 dB)

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

• Filter elements set to limit added noise over THP210 while maintaining circuit stability

• Output RC elements set by SAR input requirements

For a detailed design procedure, see Section 9.2.1.2.

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THP210

SBOS932C – JANUARY 2020 – REVISED MARCH 2021

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