Datasheet

LTC2411/LTC2411-1
26
REF
–
translates into about 0.45ppm additional INL error.
When F
O
= HIGH (internal oscillator and 50Hz notch),
every 100Ω of source resistance driving REF
+
or REF
–
translates into about 0.37ppm additional INL error. For the
LTC2411-1, when F
O
= LOW, every 100Ω of source
resistance driving REF
+
or REF
–
translates into about
0.41ppm additional INL error. When F
O
is driven by an
external oscillator with a frequency f
EOSC
, every 100Ω of
source resistance driving REF
+
or REF
–
translates into
about 2.91 • 10
–6
• f
EOSC
ppm additional INL error. Fig-
ure␣ 19 shows the typical INL error due to the source
resistance driving the REF
+
or REF
–
pins when large C
REF
values are used. The effect of the source resistance on the
two reference pins is additive with respect to this INL error.
In general, matching of source impedance for the REF
+
and REF
–
pins does not help the gain or the INL error. The
APPLICATIO S I FOR ATIO
WUUU
R
SOURCE
(Ω)
1 10 100 1k 10k 100k
–FS ERROR (ppm OF V
REF
)
2411 F17b
50
40
30
20
10
0
C
REF
= 0.01µF
C
REF
= 0.001µF
C
REF
= 100pF
C
REF
= 0pF
V
CC
= 5V
REF
+
= 5V
REF
–
= GND
IN
+
= 1.25V
IN
–
= 3.75V
F
O
= GND
T
A
= 25°C
R
SOURCE
(Ω)
0
+FS ERROR (ppm OF V
REF
)
0
–20
–40
–60
–80
–100
–120
–140
–160
800
2411 F18a
200 400 600 1000700100 300 500 900
V
CC
= 5V
REF
+
= 5V
REF
–
= GND
IN
+
= 3.75V
IN
–
= 1.25V
F
O
= GND
T
A
= 25°C
C
REF
= 0.01µF
C
REF
= 1µF
C
REF
= 0.1µF
C
REF
= 10µF
Figure 18a. +FS Error vs R
SOURCE
at REF
+
or REF
–
(Large C
IN
)
Figure 17b. –FS Error vs R
SOURCE
at REF
+
or REF
–
(Small C
IN
)
Figure 18b. –FS Error vs R
SOURCE
at REF
+
or REF
–
(Large C
IN
)
R
SOURCE
(Ω)
0
–FS ERROR (ppm OF V
REF
)
160
140
120
100
80
60
40
20
0
800
2411 F18b
200 400 600 1000700100 300 500 900
V
CC
= 5V
REF
+
= 5V
REF
–
= GND
IN
+
= 1.25V
IN
–
= 3.75V
F
O
= GND
T
A
= 25°C
C
REF
= 0.01µF
C
REF
= 1µF
C
REF
= 0.1µF
C
REF
= 10µF
V
INDIF
/V
REFDIF
–0.5–0.4–0.3–0.2–0.1 0 0.1 0.2 0.3 0.4 0.5
INL (ppm OF V
REF
)
10
9
6
4
2
0
–2
–4
–6
–8
–10
V
CC
= 5V
REF
+
= 5V
REF
–
= GND
V
INCM
= 0.5 • (IN
+
+ IN
–
) = 2.5V
F
O
= GND
C
REF
= 10µF
T
A
= 25°C
R
SOURCE
= 2k
R
SOURCE
= 1k
R
SOURCE
= 500Ω
2411 F19
Figure 19. INL vs Differential Input Voltage (V
IN
= IN
+
= IN
–
)
and Reference Source Resistance (R
SOURCE
at REF
+
and REF
–
)
for Large C
REF
Values (C
REF
≥ 1µF)
R
SOURCE
(Ω)
1 10 100 1k 10k 100k
+FS ERROR (ppm OF V
REF
)
2411 F17a
0
–10
–20
–30
–40
–50
V
CC
= 5V
REF
+
= 5V
REF
–
= GND
IN
+
= 3.75V
IN
–
= 1.25V
F
O
= GND
T
A
= 25°C
C
REF
= 0.01µF
C
REF
= 0.001µF
C
REF
= 100pF
C
REF
= 0pF
Figure 17a. +FS Error vs R
SOURCE
at REF
+
or REF
–
(Small C
IN
)