LTC2413 LINER [Linear Technology], LTC2413 Datasheet - Page 25

• Manufacturer Part Number: LTC2413
• Description: 24-Bit No Latency ADC, with Simultaneous 50Hz/60Hz Rejection
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
The effect of this input dynamic current can be analyzed
using the test circuit of Figure 17. The C
includes the LTC2413 pin capacitance (5pF typical) plus
the capacitance of the test fixture used to obtain the results
shown in Figures 18 and 19. A careful implementation can
bring the total input capacitance (C
thus achieving better performance than the one predicted
by Figures 18 and 19. For simplicity, two distinct situa-
tions can be considered.
Figure 18. +FS Error vs R
50
40
30
20
10
SWITCHING FREQUENCY
f
f
1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05
SW
SW
V
V
0
I
V
I
V
I
REF
REF
REF
REF
I
IN
IN
IN
IN
= 69900Hz INTERNAL OSCILLATOR
= 0.5 • f
+
+
–
–
+
+
–
–
V
REF
REF
IN
IN
F
T
O
CC
A
+
–
= GND
= 25 C
U
+
= 5V
= 2.5V
V
V
–
= 5V
EOSC
CC
CC
C
= 5V
= GND
C
IN
C
IN
IN
= 0.001 F
C
V
V
EXTERNAL OSCILLATOR
= 0.01 F
I
I
I
I
LEAK
LEAK
LEAK
LEAK
= 100pF
IN
CC
CC
SOURCE
U
= 0pF
R
SOURCE
I
I
I
I
LEAK
LEAK
LEAK
LEAK
( )
at IN
R
R
R
R
SW
SW
SW
SW
IN
20k
20k
20k
20k
W
(TYP)
(TYP)
(TYP)
(TYP)
+ C
+
Figure 16. LTC2413 Equivalent Analog Input Circuit
or IN
PAR
2413 F18
–
) closer to 5pF
PAR
(Small C
2413
U
F16
capacitor
IN
C
18pF
(TYP)
EQ
)
Figure 19. –FS Error vs R
I IN
I IN
I REF
I REF
where
V
V
V
V
R
R
REF
REFCM
IN
INCM
EQ
EQ
V
V
INCM
INCM
IN
AVG
AVG
: :
3 97
REF
0 555 10
+ 0.5V
– 0.5V
AVG
.
AVG
.
Figure 17. An RC Network at IN
IN
–10
–20
–30
–40
–50
M
REF
IN
V
1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05
IN
IN
IN
0
V
1 5
2
IN
REF
.
1 5
IN
INTERNAL OSCILLATOR
.
2
12
V
0 5
V
REF
REF
IN
IN
F
T
INCM
0 5
V
REF
.
V
O
A
CC
REF
+
–
INCM
.
R
R
V
/
= GND
= 25 C
SOURCE
SOURCE
+
= GND
= 2.5V
REF
f
–
= 5V
EOSC
R
0 5
C
= 5V
= GND
R
0 5
EQ
C
.
IN
C
V
EQ
.
IN
V
IN
REFCM
= 0.001 F
INCM
EXTERNAL OSCILLATOR
C
V
V
= 0.01 F
R
= 100pF
IN
REFCM
INCM
R
EQ
SOURCE
EQ
R
= 0pF
SOURCE
C
C
V
REFCM
IN
IN
V
REFCM
at IN
( )
C
C
V
+
REF
PAR
PAR
20pF
20pF
V
or IN
REF
+
V
IN
2
and IN
LTC2413
V
R
IN
2
EQ
R
2413 F19
–
EQ
IN
IN
LTC2413
(Small C
+
–
–
2413
sn2413 2413fs
F17
25
IN
)