LTC2489_15 Datasheet, PDF (19/26 Pages) Linear Technology – 16-Bit 2-/4-Channel ADC with Easy Drive Input Current Cancellation and I2C Interface

LTC2489
Applications Information
full-scale error of approximately 0.5ppm (while operating
with the internal oscillator) (see Figures 12 and 13). If
the input common mode voltage is equal to the reference
common mode voltage, a linearity error of approximately
0.67ppm per 100W of reference resistance results (see
Figure 14). In applications where the input and reference
common mode voltages are different, the errors increase.
A 1V difference in between common mode input and
common mode reference results in a 6.7ppm INL error
for every 100W of reference resistance.
In addition to the reference sampling charge, the reference
ESD protection diodes have a temperature dependent leak-
age current. This leakage current, nominally 1nA (±10nA
max) results in a small, gain error. A 100W reference
resistance will create a 0.5µV full-scale error.
Normal Mode Rejection and Antialiasing
One of the advantages delta-sigma ADCs offer over
conventional ADCs is on-chip digital filtering. Combined
with a large oversample ratio, the LTC2489 significantly
simplifies antialiasing filter requirements. Additionally,
the input current cancellation feature allows external low
pass filtering without degrading the DC performance of
the device.
The SINC⁴ digital filter provides excellent normal mode
rejection at all frequencies except DC and integer multiples
of the modulator sampling frequency (f_S). The modulator
sampling frequency is f_S = 15,360Hz while operating with
its internal oscillator and f_S = f_EOSC/20 when operating
with an external oscillator of frequency f_EOSC.
500
V_CC = 5V
400
VVV^{RIINNE+–F}
=
=
=
5V
3.75V
1.25V
f_O = GND
T_A = 25°C
300
C_REF = 1µF, 10µF
C_REF = 0.1µF
200
C_REF = 0.01µF
100
0
0
200 400 600 800 1000
R_SOURCE (Ω)
2489 F12
Figure 12. +FS Error vs R_SOURCE at V_REF (Large C_REF)
0
–100
C_REF = 0.01µF
–200
C_REF = 1µF, 10µF
–300
V_CC = 5V
–400
VVV^{RIINNE+–F}
=
=
=
5V
1.25V
3.75V
f_O = GND
T_A = 25°C
–500
0
200 400 600
R_SOURCE (Ω)
C_REF = 0.1µF
800 1000
2489 F13
Figure 13. –FS Error vs R_SOURCE at V_REF (Large C_REF)
10
V_CC = 5V
8 V_REF = 5V
6
V_IN(CM) = 2.5V
T_A = 25°C
4 ^CREF ^{= 10µF}
R = 1k
2
R = 500Ω
0
–2
R = 100Ω
–4
–6
–8
–10
–0.5 –0.3 –0.1 0.1
0.3
0.5
V_IN/V_REF
2489 F14
Figure 14. INL vs Differential Input Voltage and
Reference Source Resistance for C_REF > 1µF
For more information www.linear.com/LTC2489
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