Datasheet
ADS1281
www.ti.com
SBAS378D –AUGUST 2007–REVISED JUNE 2010
ELECTRICAL CHARACTERISTICS
Limit specifications at –40°C to +85°C, typical specifications at +25°C, AVDD = +2.5V, AVSS = –2.5V, f
CLK
(1)
= 4.096MHz, VREFP = +2.5V,
VREFN = –2.5V, DVDD = +3.3V, and f
DATA
= 1000SPS, unless otherwise noted.
ADS1281
PARAMETER CONDITIONS MIN TYP MAX UNIT
ANALOG INPUTS
Full-scale input voltage V
IN
= AINP – AINN ±V
REF
/2 V
Absolute input range AINP or AINN AVSS – 0.1 AVDD + 0.1 V
Differential input impedance 55 kΩ
AC PERFORMANCE
f
DATA
= 250SPS 130
f
DATA
= 500SPS 127
Signal-to-noise ratio
(2)
SNR f
DATA
= 1000SPS 120 124 dB
f
DATA
= 2000SPS 121
f
DATA
= 4000SPS 118
Total harmonic distortion THD –122 –115 dB
V
IN
= 31.25Hz, –0.5dBFS
Spurious-free dynamic
SFDR 123 dB
range
(3)
DC PERFORMANCE
Resolution No missing codes 31 Bits
FIR filter mode 250 4000 SPS
Data rate f
DATA
Sinc filter mode 8,000 128,000 SPS
Integral nonlinearity
(4)
INL Differential input 0.00006 0.0005 % FSR
(5)
Offset error 10 200 mV
Offset error after calibration
(6)
Shorted input 1 mV
Offset drift 0.06 mV/°C
Gain error 0.1 0.3 %
Gain error after calibration
(6)
0.0002 %
Gain drift 0.4 ppm/°C
Common-mode rejection f
CM
= 60Hz 105 120 dB
AVDD, AVSS 85 95
Power-supply rejection f
PS
= 60Hz dB
DVDD 85 105
FIR DIGITAL FILTER RESPONSE
Passband ripple ±0.003 dB
Passband (–0.01dB) 0.375 × f
DATA
Hz
Stop band attenuation
(7)
135 dB
Stop band 0.500 × f
DATA
Hz
Bandwidth (–3dB) 0.413 × f
DATA
Hz
FIR filter, minimum phase
(8)
5/f
DATA
Group delay s
FIR filter, linear phase 31/f
DATA
FIR filter, minimum phase 62/f
DATA
Settling time (latency) s
FIR filter, linear phase 62/f
DATA
High-pass filter corner 0.1 10 Hz
(1) f
CLK
= system clock.
(2) SNR = signal-to-noise ratio = 20 log (V
RMS
Full-Scale/V
RMS
Noise), V
IN
= 20mV
DC
.
(3) Highest spurious component including harmonics.
(4) Best-fit method.
(5) FSR: Full-scale range = ±V
REF
/2.
(6) Calibration accuracy is on the level of noise reduced by 4 (calibration averages 16 readings).
(7) Input frequencies in the range of Nf
CLK
/512 ± f
DATA
/2 (N = 1, 2, 3...) can mix with the modulator chopping clock. In these frequency
ranges intermodulation = 120dB, typ.
(8) At dc; see Figure 32.
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