LTC2410 Linear Technology, LTC2410 Datasheet - Page 25

• Manufacturer Part Number: LTC2410
• Description: 24-Bit No Latency ADC with Differential Input and Differential Reference
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
Figure 26. INL vs Differential Input Voltage (V
and Reference Source Resistance (R
Large C
The magnitude of the dynamic reference current depends
upon the size of the very stable internal sampling capaci-
tors and upon the accuracy of the converter sampling
clock. The accuracy of the internal clock over the entire
temperature and power supply range is typical better than
0.5%. Such a specification can also be easily achieved by
an external clock. When relatively stable resistors
(50ppm/ C) are used for the external source impedance
seen by REF
current gain error will be insignificant (about 1% of its
value 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 reference sampling charge, the reference
pins ESD protection diodes have a temperature dependent
leakage current. This leakage current, nominally 1nA
( 10nA max), results in a small gain error. A 100 source
resistance will create a 0.05 V typical and 0.5 V maxi-
mum full-scale error.
Output Data Rate
When using its internal oscillator, the LTC2410 can pro-
duce up to 7.5 readings per second with a notch frequency
of 60Hz (F
notch frequency of 50Hz (F
REF
Values (C
O
–12
–15
= LOW) and 6.25 readings per second with a
+
–3
–6
–9
15
12
9
6
3
0
–0.5 –0.4–0.3–0.2–0.1 0 0.1 0.2 0.3 0.4 0.5
and REF
V
REF+ = 5V
REF– = GND
V
CC
INCM
R
= 5V
REF
SOURCE
U
= 0.5 • (IN
–
, the expected drift of the dynamic
1 F)
= 100
V
R
U
+
INDIF
SOURCE
+ IN
O
/V
R
= HIGH). The actual output
–
SOURCE
REFDIF
) = 2.5V
= 1000
SOURCE
W
= 500
F
C
T
O
REF
A
at REF
= GND
= 25 C
IN
= 10 F
2410 F26
= IN
+
+
and REF
– IN
U
–
)
–
for
data rate will depend upon the length of the sleep and data
output phases which are controlled by the user and which
can be made insignificantly short. When operated with an
external conversion clock (F
oscillator), the LTC2410 output data rate can be increased
as desired. The duration of the conversion phase is 20510/
f
internal oscillator is used and the notch is set at 60Hz.
There is no significant difference in the LTC2410 perfor-
mance between these two operation modes.
An increase in f
translate into a proportional increase in the maximum
output data rate. This substantial advantage is neverthe-
less accompanied by three potential effects, which must
be carefully considered.
First, a change in f
in the internal notch position and in a reduction of the
converter differential mode rejection at the power line
frequency. In many applications, the subsequent perfor-
mance degradation can be substantially reduced by rely-
ing upon the LTC2410’s exceptional common mode rejec-
tion and by carefully eliminating common mode to differ-
ential mode conversion sources in the input circuit. The
user should avoid single-ended input filters and should
maintain a very high degree of matching and symmetry in
the circuits driving the IN
Second, the increase in clock frequency will increase
proportionally the amount of sampling charge transferred
through the input and the reference pins. If large external
input and/or reference capacitors (C
previous section provides formulae for evaluating the
effect of the source resistance upon the converter perfor-
mance for any value of f
or reference capacitors (C
the external source resistance upon the LTC2410 typical
performance can be inferred from Figures 17, 18, 22 and
23 in which the horizontal axis is scaled by 153600/f
Third, an increase in the frequency of the external oscilla-
tor above 460800Hz (a more than 3 increase in the output
data rate) will start to decrease the effectiveness of the
internal autocalibration circuits. This will result in a pro-
gressive degradation in the converter accuracy and linear-
EOSC
. If f
EOSC
= 153600Hz, the converter behaves as if the
EOSC
EOSC
will result in a proportional change
over the nominal 153600Hz will
EOSC
+
IN
and IN
, C
. If small external input and/
O
REF
connected to an external
) are used, the effect of
–
IN
pins.
, C
LTC2410
REF
) are used, the
25
EOSC
.