LTC2410 Linear Technology, LTC2410 Datasheet - Page 21

• Manufacturer Part Number: LTC2410
• Description: 24-Bit No Latency ADC with Differential Input and Differential Reference
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
The effect of this input dynamic current can be analyzed
using the test circuit of Figure 16. The C
includes the LTC2410 pin capacitance (5pF typical) plus
the capacitance of the test fixture used to obtain the results
shown in Figures 17 and 18. A careful implementation can
bring the total input capacitance (C
thus achieving better performance than the one predicted
by Figures 17 and 18. For simplicity two distinct situations
can be considered.
Figure 17. +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
= 76800Hz INTERNAL OSCILLATOR (F
= 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 15. LTC2410 Equivalent Analog Input Circuit
or IN
PAR
O
= LOW OR HIGH)
2410 F17
–
) closer to 5pF
PAR
(Small C
2410 F15
U
capacitor
IN
C
18pF
(TYP)
EQ
)
Figure 18. –FS Error vs R
I IN
I IN
I REF
I REF
R
R
R
where
V
V
V
V
REF
REFCM
IN
INCM
EQ
EQ
EQ
V
V
INCM
INCM
IN
AVG
AVG
: :
3 61
4 32
REF
0 555 10
AVG
.
.
AVG
.
+ 0.5V
– 0.5V
IN
Figure 16. An RC Network at IN
M
M
REF
IN
V
–10
–20
–30
–40
–50
IN
V
1 5
2
1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05
IN
REF
.
0
INTERNAL OSCILLATOR
IN
INTERNAL OSCILLATOR
IN
IN
1 5
.
12
V
2
0 5
INCM
0 5
V
REF
.
V
REF
INCM
.
V
/
V
REF
REF
IN
IN
F
T
REF
f
O
A
EOSC
CC
R
0 5
+
–
R
R
R
= GND
0 5
= 25 C
EQ
.
+
= GND
= 2.5V
–
V
EQ
.
SOURCE
SOURCE
= 5V
V
REFCM
C
= 5V
= GND
INCM
V
EXTERNAL OSCILLATOR
V
C
R
IN
REFCM
INCM
C
R
IN
EQ
IN
EQ
= 0.001 F
C
= 0.01 F
= 100pF
IN
V
SOURCE
REFCM
R
= 0pF
V
SOURCE
REFCM
C
C
60
IN
IN
50
Hz Notch F
Hz Notch F
V
at IN
REF
( )
V
REF
V
IN
2
V
R
IN
2
C
C
+
EQ
R
PAR
PAR
20pF
20pF
EQ
or IN
+
O
O
and IN
LTC2410
LOW
HIGH
2410 F18
–
IN
IN
LTC2410
(Small C
+
–
–
2410 F16
21
IN
)