
LTC2494
2494fd
applications inForMation
100pF up to 10k will not degrade the performance) (see
Figures 14, 15).
In cases where large bypass capacitors are required
on the reference inputs (CREF > 0.01F) full-scale and
linearity errors are proportional to the value of the refer-
ence resistance. Every ohm of reference resistance pro-
duces a full-scale error of approximately 0.5ppm (while
operating in simultaneous 50Hz/60Hz mode) (see Figures
16 and 17). If the input common mode voltage is equal to
the reference common mode voltage, a linearity error of
approximately 0.67ppm per 100
Ω of reference resistance
results (see Figure 18). In applications where the input
and reference common mode voltages are different, the
errorsincrease.A1Vdifferenceinbetweencommonmode
input and common mode reference results in a 6.7ppm
INL error for every 100
Ω of reference resistance.
Figure 16. +FS Error vs RSOURCE at VREF (Large CREF)
Figure 17. –FS Error vs RSOURCE at VREF (Large CREF)
Figure 18. INL vs Differential Input Voltage and
Reference Source Resistance for CREF > 1F
Figure 14. +FS Error vs RSOURCE at VREF (Small CREF)
Figure 15. –FS Error vs RSOURCE at VREF (Small CREF)
RSOURCE ()
0
+FS
ERROR
(ppm)
50
70
90
10k
2494 F14
30
10
40
60
80
20
0
–10
10
100
1k
100k
VCC = 5V
VREF = 5V
VIN+ = 3.75V
VIN– = 1.25V
fO = GND
TA = 25°C
CREF = 0.01F
CREF = 0.001F
CREF = 100pF
CREF = 0pF
RSOURCE ()
0
–FS
ERROR
(ppm) –30
–10
10
10k
2494 F15
–50
–70
–40
–20
0
–60
–80
–90
10
100
1k
100k
VCC = 5V
VREF = 5V
VIN+ = 1.25V
VIN– = 3.75V
fO = GND
TA = 25°C
CREF = 0.01F
CREF = 0.001F
CREF = 100pF
CREF = 0pF
RSOURCE ()
0
+FS
ERROR
(ppm) 300
400
500
800
2494 F16
200
100
0
200
400
600
1000
VCC = 5V
VREF = 5V
VIN+ = 3.75V
VIN– = 1.25V
fO = GND
TA = 25°C
CREF = 1F, 10F
CREF = 0.1F
CREF = 0.01F
RSOURCE ()
0
–FS
ERROR
(ppm) –200
–100
0
800
2494 F17
–300
–400
–500
200
400
600
1000
VCC = 5V
VREF = 5V
VIN+ = 1.25V
VIN– = 3.75V
fO = GND
TA = 25°C
CREF = 1F, 10F
CREF = 0.1F
CREF = 0.01F
VIN/VREF (V)
–0.5
INL
(ppm
OF
V
REF
)
2
6
10
0.3
2494 F18
–2
–6
0
4
8
–4
–8
–10
–0.3
–0.1
0.1
0.5
VCC = 5V
VREF = 5V
VIN(CM) = 2.5V
TA = 25°C
CREF = 10F
R = 1k
R = 100
R = 500