ADS1113 datasheet(32/49 Pages) TI2

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9.2.2.7 Circuit Implementation

Table 9-2 shows the chosen values for this design.

Table 9-2. Parameters

PARAMETER

VALUE

VCM

2.5V

FSR of ADC

±0.256V

Output data rate

250SPS

R1, R3

1kΩ(1)

R2, R4

5kΩ(1)

R5, R6

100Ω(1)

CDIFF

0.22µF

CCM1, CCM2

0.022µF

(1)

1% precision resistors are used.

Using Equation 5, if VSHUNT ranges from –50mV to +50mV, the application circuit produces a differential voltage

ranging from –0.250V to +0.250V across the ADC inputs. The ADC is therefore configured at a FSR of ±0.256V

to maximize the dynamic range of the ADC.

The –3dB cutoff frequencies of the differential low-pass filter and the common-mode low-pass filters are set at

3.6kHz and 0.36kHz, respectively.

RSHUNT typically ranges from 0.01mΩ to 100mΩ. Therefore, if R1 = R3 = 1kΩ, a good trade-off exists between

the circuit input impedance and input-referred resistor noise as explained in the Noise and Input Impedance

Considerations section.

A simple resistor divider followed by a buffer amplifier is used to generate VCM of 2.5V from a 5V supply.

9.2.2.8 Results Summary

A precision voltage source is used to sweep VSHUNT from –50mV to +50mV. The application circuit produces

a differential voltage of –250mV to +250mV across the ADC inputs. Figure 9-7 and Figure 9-8 show the

measurement results. The measurements are taken at TA = 25°C. Although 1% tolerance resistors are used,

the exact value of these resistors are measured with a Fluke 4.5 digit multimeter to exclude the errors due

to inaccuracy of these resistors. In Figure 9-7, the x-axis represents VSHUNT and the black line represents the

measured digital output voltage in mV. In Figure 9-8, the x-axis represents VSHUNT, the black line represents

the total measurement error in %, the blue line represents the total measurement error in % after excluding the

errors from precision resistors and the green line represents the total measurement error in % after excluding the

errors from precision resistors and performing a system offset calibration with VSHUNT = 0V. Table 9-3 shows a

results summary.

Table 9-3. Results Summary (1)

PARAMETER

VALUE

Total error, including errors from 1% precision resistors

1.89%

Total error, excluding errors from 1% precision resistors

0.17%

Total error, after offset calibration, excluding errors from 1% precision resistors

0.11%

(1)

TA = 25°C, not accounting for inaccuracy of shunt resistor.

ADS1013, ADS1014, ADS1015

SBAS473F – MAY 2009 – REVISED JANUARY 2025

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