LTC2420IS8 Linear Technology, LTC2420IS8 Datasheet - Page 25

• Manufacturer Part Number: LTC2420IS8
• Description: IC ADC 20BIT MICROPOWER 8SOIC
• Manufacturer: Linear Technology

Specifications of LTC2420IS8

• Number Of Bits: 20
• Sampling Rate (per Second): 7.5
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 2
• Power Dissipation (max): 1mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
node V
can tolerate large external resistances without reduction
in INL, see Figure 25. If the external capacitance is large
(C
0.015ppm/
Figure 26.
In addition to the dynamic reference current, the V
protection diodes have a temperature dependent leakage
current. This leakage current, nominally 1nA ( 10nA max),
results in a fixed full-scale shift of 10 V for a 10k source
resistance.
VREF
REF
> 0.01 F), the linearity will be degraded by
Figure 24. Full-Scale Error vs R
Figure 23. Full-Scale Error vs R
–100
–200
–10
500
400
300
200
100
60
is small (C
50
40
30
20
10
0
0
1
0
V
V
V
T
V
V
V
T
independent of capacitance at V
A
A
CC
REF
IN
CC
REF
IN
= 25 C
= 25 C
= 5V
= 5V
= 5V
= 5V
= 5V
= 5V
200
10
C
C
C
C
C
C
U
VREF
VREF
VREF
VREF
VREF
VREF
RESISTANCE AT V
RESISTANCE AT V
VREF
= 22 F
= 10 F
= 1 F
= 0.1 F
= 0.01 F
= 0.001 F
400
100
C
C
VREF
C
VREF
U
VREF
< 0.01 F), the reference input
= 1000pF
= 0.01 F
= 100pF
600
1k
REF
REF
( )
( )
C
VREF
W
10k
800
VREF
VREF
= 0pF
2420 F23
2420 F24
(Small C)
(Large C)
1000
100k
U
REF
REF
, see
ESD
ANTIALIASING
One of the advantages delta-sigma ADCs offer over con-
ventional ADCs is on-chip digital filtering. Combined with
a large oversampling ratio, the LTC2420 significantly
simplifies antialiasing filter requirements.
The digital filter provides very high rejection except at
integer multiples of the modulator sampling frequency
(f
256 • F
or 60Hz). The bandwidth of signals not rejected by the
digital filter is narrow ( 0.2%) compared to the bandwidth
of the frequencies rejected.
S
), see Figure 27. The modulator sampling frequency is
O
, where F
–10
–20
–10
50
20
10
40
30
10
–2
–4
–6
–8
Figure 25. INL Error vs R
Figure 26. INL Error vs R
0
8
6
4
2
0
1
0
V
V
T
CC
REF
A
= 25 C
= 5V
O
= 5V
200
10
C
C
C
C
C
C
is the notch frequency (typically 50Hz
VREF
VREF
VREF
VREF
VREF
VREF
C
RESISTANCE AT V
RESISTANCE AT V
VREF
C
C
VREF
VREF
= 22 F
= 10 F
= 1 F
= 0.1 F
= 0.01 F
= 0.001 F
100
= 0.01 F
400
= 1000pF
= 100pF
600
1k
REF
REF
VREF
VREF
( )
( )
C
VREF
10k
V
V
T
800
A
CC
REF
(Small C)
(Large C)
= 25 C
= 0pF
= 5V
2420 F25
2420 F26
= 5V
LTC2420
100k
1000
25