LTC2412 Linear Technology, LTC2412 Datasheet - Page 28

• Manufacturer Part Number: LTC2412
• Description: 2-Channel Differential Input 24-Bit No Latency DS ADC
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
LTC2412
(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 LTC2412 can pro-
duce up to 7.5 readings per second with a notch frequency
of 60Hz (F
notch frequency of 50Hz (F
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 LTC2412 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.
28
EOSC
Figure 22. INL vs Differential Input Voltage (V
and Reference Source Resistance (R
for Large C
. If f
EOSC
–12
–15
O
–3
–6
–9
15
12
REF
9
6
3
0
= LOW) and 6.25 readings per second with a
–0.5 –0.4–0.3–0.2–0.1 0 0.1 0.2 0.3 0.4 0.5
+
V
REF+ = 5V
REF– = GND
V
and REF
= 153600Hz, the converter behaves as if the
CC
INCM
Values (C
R
= 5V
SOURCE
= 0.5 • (IN
U
–
= 100
REF
, the expected drift of the dynamic
V
R
+
INDIF
SOURCE
+ IN
U
O
/V
R
1 F)
–
SOURCE
REFDIF
) = 2.5V
O
= HIGH). The actual output
= 1000
connected to an external
SOURCE
= 500
F
C
T
W
O
A
REF
= GND
= 25 C
= 10 F
2412 F22
at REF
IN
= IN
+
and REF
U
+
– IN
–
)
–
There is no significant difference in the LTC2412 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 LTC2412’s exceptional common mode
rejection and by carefully eliminating common mode to
differential 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 LTC2412 typical
performance can be inferred from Figures 13, 14, 18 and
19 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-
ity. Typical measured performance curves for output data
rates up to 100 readings per second are shown in Fig-
ures 23, 24, 25, 26, 27, 28, 29 and 30. In order to obtain
the highest possible level of accuracy from this converter
at output data rates above 20 readings per second, the
user is advised to maximize the power supply voltage used
and to limit the maximum ambient operating temperature.
In certain circumstances, a reduction of the differential
reference voltage may be beneficial.
EOSC
EOSC
will result in a proportional change
over the nominal 153600Hz will
EOSC
IN
, C
. If small external input and/
REF
) are used, the effect of
IN
, C
+
REF
and IN
) are used, the
–
pins.
EOSC
2412f
.