Datasheet

25
LTC2401/LTC2402
on the offset. However, the reference current at V
IN
= V
REF
is similar to the input current at full-scale. For large values
of reference capacitance (C
VREF
> 0.01µF), the full-scale
error shift is 0.08ppm/Ω of external reference resistance
independent of the capacitance at V
REF
, see Figure 22. If
the capacitance tied to V
REF
is small (C
VREF
< 0.01µF), an
input resistance of up to 20k (20pF parasitic capacitance
at V
REF
) may be tolerated, see Figure 23.
Unlike the analog input, the integral nonlinearity of the
device can be degraded with excessive external RC time
constants tied to the reference input. If the capacitance
APPLICATIO S I FOR ATIO
WUUU
Figure 22. Full-Scale Error vs R
VREF
(Large C)
Figure 23. Full-Scale Error vs R
VFEF
(Small C)
Figure 24. INL Error vs R
VREF
(Small C)
Figure 25. INL Error vs R
VREF
(Large C)
at node V
REF
is small (C
VREF
< 0.01µF), the reference input
can tolerate large external resistances without reduction
in INL, see Figure 24. If the external capacitance is large
(C
VREF
> 0.01µF), the linearity will be degraded by
0.04ppm/Ω independent of capacitance at V
REF
, see
Figure 25.
In addition to the dynamic reference current, the V
REF
ESD
protection diodes have a temperature dependent leakage
current. This leakage current, nominally 1nA (±10nA max),
results in a fixed full-scale shift of 10µV for a 10k source
resistance.
RESISTANCE AT V
REF
(Ω)
0
FULL-SCALE ERROR (ppm)
80
120
800
24012 F22
40
0
200
400
600
1000
160
V
CC
= 5V
V
REF
= 5V
V
IN
= 5V
T
A
= 25°C
C
IN
= 10µF
C
IN
= 0.1µF
C
IN
= 0.01µF
C
IN
= 1µF
RESISTANCE AT V
REF
(Ω)
100
–50
FULL-SCALE ERROR (ppm)
–25
0
25
50
C
IN
= 10µF
1k 10k
24012 F23
100k
V
CC
= 5V
V
REF
= 5V
V
IN
= 5V
T
A
= 25°C
C
IN
= 20pF
C
IN
= 1000pF
C
IN
= 100pF
RESISTANCE AT V
REF
(Ω)
100
0
INL ERROR (ppm)
10
20
C
IN
= 0.01µF
C
IN
= 20pF
C
IN
= 1000pF
C
IN
= 100pF
30
40
50
V
CC
= 5V
V
REF
= 5V
T
A
= 25°C
1k 10k
24012 F24
100k
RESISTANCE AT V
REF
(Ω)
0
INL ERROR (ppm)
20
30
800
24012 F25
10
0
200
400
600
1000
40
V
CC
= 5V
V
REF
= 5V
T
A
= 25°C
C
VREF
= 10µF
C
VREF
= 0.1µF
C
VREF
= 1µF
C
VREF
= 0.01µF