ltc2493 Linear Technology Corporation, ltc2493 Datasheet - Page 25

• Manufacturer Part Number: ltc2493
• Description: 24-bit 2-/4-channel Delta Sigma Adc With Easy Drive Input Current Cancellation And I2c Interface
• Manufacturer: Linear Technology Corporation

applicaTions inForMaTion
the reference common mode voltage, a linearity error of
approximately 0.67ppm per 100W 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 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 LTC2493 significantly
simplifies antialiasing filter requirements. Additionally,
the input current cancellation feature allows external low
pass filtering without degrading the DC performance of
the device.
Figure 16. INL vs Differential Input Voltage and
Reference Source Resistance for C
–10
10
–2
–4
–6
–8
8
6
4
2
0
– 0.5
V
V
V
T
C
A
CC
REF
IN(CM)
REF
= 25°C
= 5V
= 5V
= 10µF
– 0.3
= 2.5V
– 0.1
V
IN
/V
REF
0.1
R = 500Ω
R = 100Ω
R = 1k
0.3
REF
2493 F16
> 1µF
0.5
The SINC
rejection at all frequencies except DC and integer multiples
of the modulator sampling frequency (f
17 and 18). The modulator sampling frequency is f
15,360Hz while operating with its internal oscillator and
f
of frequency f
S
= f
EOSC
Figure 17. Input Normal Mode Rejection, Internal
Oscillator and 50Hz Rejection Mode
Figure 18. Input Normal Mode Rejection, Internal
Oscillator and 60Hz Rejection Mode
4
/20 when operating with an external oscillator
–100
–110
–120
–100
–110
–120
–10
–20
–30
–40
–50
–60
–70
–80
–90
–10
–20
–30
–40
–50
–60
–70
–80
–90
digital filter provides excellent normal mode
0
0
0
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
EOSC
0 f
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
f
S
S
2f
.
2f
S
S
3f
S
3f
4f
S
S
4f
5f
S
S
5f
6f
S
S
7f
6f
S
S
8f
7f
S
S
9f
S
8f
10f
S
LTC2493
S
9f
11f
2493 F18
2493 F17
S
S
) (see Figures
S
10f
12f
S
S

2493fa
S
=