LTC2439-1 Linear Technology, LTC2439-1 Datasheet - Page 25

• Manufacturer Part Number: LTC2439-1
• Description: 8-/16-Channel 16-Bit No Latency Delta-Sigma ADC
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
impedance for the REF
gain or the INL error. The user is thus advised to minimize
the combined source impedance driving the REF
REF
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
Figure 21. +FS Error vs R
Figure 23. INL vs Differential Input Voltage (V
and Reference Source Resistance (R
for Large C
–
pins rather than to try to match it.
REF
–1
1
0
+
–0.5 –0.4–0.3–0.2–0.1 0 0.1 0.2 0.3 0.4 0.5
11
17
22
30
and REF
V
REF+ = 5V
REF– = GND
V
0
6
Values (C
CC
INCM
0 100 200 300 400 500 600 700 800 900 1000
V
REF
REF
IN
IN
F
T
= 5V
O
CC
A
+
–
= 0.5 • (IN
= GND
= 25 C
U
+
–
= 3.75V
= 1.25V
= 5V
= 5V
= GND
–
SOURCE
+
REF
, the expected drift of the dynamic
V
and REF
+
INDIF
U
+ IN
R
SOURCE
1 F)
/V
–
at REF
) = 2.5V
REFDIF
C
R
REF
SOURCE
( )
–
SOURCE
= 1 F, 10 F
pins does not help the
C
W
+
C
REF
REF
F
C
T
and REF
O
REF
A
= 1000
= GND
= 25 C
= 0.01 F
= 0.1 F
= 10 F
24361 F23
at REF
IN
24361 F21
–
= IN
(Large C
+
U
and REF
+
– IN
+
–
REF
)
and
–
)
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 LTC2439-1 can
produce up to 6.8 readings per second. The actual output
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 LTC2439-1 output data rate can be in-
creased as desired. The duration of the conversion phase
is 20510/f
haves as if the internal oscillator is used with simultaneous
50Hz/60Hz. There is no significant difference in the
LTC2439-1 performance 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.
Figure 22. –FS Error vs R
EOSC
30
22
17
11
6
0
. If f
0 100 200 300 400 500 600 700 800 900 1000
V
REF
REF
IN
IN
F
T
EOSC
O
A
CC
+
–
= GND
= 25 C
+
–
= 1.25V
= 3.75V
= 5V
EOSC
= 5V
= GND
SOURCE
over the nominal 139,800Hz will
= 139,800Hz, the converter be-
R
SOURCE
at REF
O
C
connected to an external
REF
( )
C
REF
= 1 F, 10 F
+
C
LTC2439-1
REF
= 0.01 F
and REF
= 0.1 F
24361 F22
–
(Large C
25
REF
24391f
)