INA821 datasheet(35/52 Pages) TI

35 / 52 page

-10

-5

Input Voltage (V)

Figure 9-4. PLC Output Voltage vs Input Voltage

C001

-20

-10

Input Current (mA)

C001

Figure 9-5. PLC Output Voltage vs Input Current

9.2.2 20-Bit, 1-MSPS ADS8900B Driver Circuit With FDA Noise Filter

The application circuit in Figure 9-6 shows the schematic of a complete input and reference driver circuit for the

ADS8900B, a 20-bit, precision, 1-MSPS, successive approximation register (SAR), analog-to-digital converter

(ADC). This circuit is used to measure the driving capability of the INA851 with the ADS8900B 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 noise caused by supply voltage, the test circuit uses the TPS7A4700, a low-noise 4-µVRMS, RF

LDO voltage regulator, to generate the 5.2-V supply rail.

For VOCM, the circuit uses the REF5050, a low-noise, low-drift, 5-V reference, a 20k-20k voltage divider to

establish VREF/2 and an additional RC filter (10 Ω, 150 pF) into the VOCM pin. See also the ADS8900EVM-

PDK user's guide.

–

VS+

OUT+

IN+

RG+

OUT

VOCM

G02

G02+

3 k

5 k

3 k

5 k

1.25 k

5 k

1.25 k

LDO

VCLAMP+

VCLAMP

ADS8900B

INP

INN

FDA_IN

FDA_IN+

–

INA851

15 V

5.0 V

OVP

–

VDD

VSS

VIN+

VIN-

150 pF

CFB

RFIL

CFIL

VREF

5.2 V

VREF/2

47.4

1 nF

Figure 9-6. Driving ADS8900B With FDA Noise Filter

www.ti.com

INA851

SBOS999A – MARCH 2022 – REVISED OCTOBER 2022

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