LTC2435CGN Linear Technology, LTC2435CGN Datasheet - Page 28

• Manufacturer Part Number: LTC2435CGN
• Description: IC ADC DIFF I/REF 20BIT 16-SSOP
• Manufacturer: Linear Technology

Specifications of LTC2435CGN

• Number Of Bits: 20
• Sampling Rate (per Second): 15
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 2
• Power Dissipation (max): 1mW
• Voltage Supply Source: Single Supply
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP (0.150", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

LTC2435/LTC2435-1
APPLICATIO S I FOR ATIO
gain errors will be insignificant (about 1% of their respec-
tive values over the entire temperature and voltage range).
Even for the most stringent applications, a one-time
calibration operation may be sufficient.
In addition to the input sampling charge, the input ESD
protection diodes have a temperature dependent leakage
current. This current, nominally 1nA (±10nA max), results
in a small offset shift. A 100Ω source resistance will create
a 0.1μV typical and 1μV maximum offset voltage.
Reference Current
In a similar fashion, the LTC2435/LTC2435-1 sample the
differential reference pins REF
small amount of charge to and from the external driving
circuits thus producing a dynamic reference current. This
current does not change the converter offset, but it may
degrade the gain and INL performance. The effect of this
current can be analyzed in the same two distinct situa-
tions.
For relatively small values of the external reference capaci-
tors (C
settles almost completely and relatively large values for
the source impedance result in only small errors. Such
values for C
gain performance without significant benefits of reference
filtering and the user is advised to avoid them.
28
Figure 21. +FS Error vs R
REF
< 0.01μF), the voltage on the sampling capacitor
REF
100
–10
90
80
70
60
50
40
30
20
10
0
1
will deteriorate the converter offset and
V
V
V
V
V
F
T
O
A
CC
REF +
REF –
IN
IN –
= GND
= 25°C
+
= 5V
U
= 3.75V
= 1.25V
= 5V
= GND
10
SOURCE
C
IN
U
100
R
C
= 0.001μF
SOURCE
IN
C
IN
= 100pF
at REF
= 0.01μF
+
1000
(Ω)
and REF
W
+
10000
or REF
C
IN
= 0pF
2435 F21
–
100000
–
(Small C
transferring
U
IN
)
Larger values of reference capacitors (C
be required as reference filters in certain configurations.
Such capacitors will average the reference sampling charge
and the external source resistance will see a quasi con-
stant reference differential impedance. For the LTC2435,
when F
typical differential reference resistance is 15.6MΩ which
will generate a +FS gain error of approximately 0.032ppm
for each ohm of source resistance driving REF
When F
typical differential reference resistance is 18.7MΩ which
will generate a +FS gain error of approximately 0.027ppm
for each ohm of source resistance driving REF
For the LTC2435-1, the typical differential reference resis-
tance is 17.1MΩ which will generate a +FS gain error of
approximately 0.029ppm for each ohm of source resis-
tance driving REF
external oscillator with a frequency f
sion clock operation), the typical differential reference
resistance is 2.4 • 10
resistance driving REF
0.21 • 10
source resistance on the two reference pins is additive
with respect to this gain error. The typical +FS and –FS
errors for various combinations of source resistance seen
by the REF
connected to these pins are shown in Figures 21, 22, 23
and 24.
Figure 22. –FS Error vs R
O
O
= LOW (internal oscillator and 60Hz notch), the
= HIGH (internal oscillator and 50Hz notch), the
–6
+
–100
• f
and REF
–40
–50
–60
–80
–90
–10
–20
–30
–70
10
0
EOSC
1
V
V
V
V
V
F
T
O
CC
REF +
REF
IN +
IN –
A
+
= GND
= 25°C
ppm +FS gain error. The effect of the
= 5V
–
= 1.25V
= 3.75V
–
or REF
= 5V
= GND
10
12
pins and external capacitance C
/f
SOURCE
C
EOSC
IN
C
IN
100
R
= 0.01μF
+
C
SOURCE
–
= 0.001μF
IN
. When F
Ω and each ohm of source
or REF
= 100pF
at REF
1000
(Ω)
EOSC
+
10000
or REF
–
O
C
REF
IN
(external conver-
is driven by an
will result in
= 0pF
2435 F22
> 0.01μF) may
100000
–
(Small C
+
+
or REF
or REF
24351fb
IN
REF
)
–
–
.
.