Datasheet

LTC2493
25
2493fd
The SINC
4
digital filter provides excellent normal mode
rejection at all frequencies except DC and integer multiples
of the modulator sampling frequency (f
S
) (see Figures
17 and 18). 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
.
Figure 16. INL vs Differential Input Voltage and
Reference Source Resistance for C
REF
> 1µF
Figure 18. Input Normal Mode Rejection, Internal
Oscillator and 60Hz Rejection Mode
Figure 17. Input Normal Mode Rejection, Internal
Oscillator and 50Hz Rejection Mode
the reference common mode voltage, a linearity error of
approximately 0.67ppm per 100Ω of reference resistance
results (see Figure 16). 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 100Ω 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 100Ω reference
resistance will create a 0.5µV full-scale error.
Normal Mode Rejection and Anti-Aliasing
One of the advantages delta-sigma ADCs offer over
conventional ADCs is on-chip digital filtering. Combined
with a large oversample ratio, the LTC2493 significantly
simplifies anti-aliasing filter requirements. Additionally,
the input current cancellation feature allows external
lowpass filtering without degrading the DC performance
of the device.
applicaTions inForMaTion
V
IN
/V
REF
–0.5
INL (ppm OF V
REF
)
2
6
10
0.3
2493 F16
–2
–6
0
4
8
–4
–8
–10
–0.3
–0.1
0.1
0.5
V
CC
= 5V
V
REF
= 5V
V
IN(CM)
= 2.5V
T
A
= 25°C
C
REF
= 10µF
R = 1k
R = 100Ω
R = 500Ω
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
0 f
S
2f
S
3f
S
4f
S
5f
S
6f
S
7f
S
8f
S
9f
S
10f
S
11f
S
12f
S
INPUT NORMAL MODE REJECTION (dB)
2493 F17
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
0 f
S
INPUT NORMAL MODE REJECTION (dB)
2493 F18
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
2f
S
3f
S
4f
S
5f
S
6f
S
7f
S
8f
S
9f
S
10f
S