ltc2415-1 Linear Technology Corporation, ltc2415-1 Datasheet - Page 27

• Manufacturer Part Number: ltc2415-1
• Description: 24-bit No Latency Delta Sigma Adc With Differential Input And Differential Reference
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
incomplete settling of the input signal sampling process
may result in gain and offset errors, but it will not degrade
the INL performance of the converter. Figure 18 shows the
mathematical expressions for the average bias currents
flowing through the IN
sampling charge transfers when integrated over a sub-
stantial time period (longer than 64 internal clock cycles).
The effect of this input dynamic current can be analyzed
using the test circuit of Figure 19. The C
includes the LTC2415/LTC2415-1 pin capacitance (5pF
typical) plus the capacitance of the test fixture used to
obtain the results shown in Figures 20 and 21. A careful
implementation can bring the total input capacitance (C
+ C
than the one predicted by Figures 20 and 21. For simplic-
ity, two distinct situations can be considered.
V
V
I
V
V
I
REF
REF
I
I
REF
REF
IN
IN
IN
IN
PAR
+
+
–
–
+
+
–
–
V
V
INCM
INCM
) closer to 5pF thus achieving better performance
V
V
CC
CC
+ 0.5V
– 0.5V
Figure 19. An RC Network at IN
V
V
I
I
I
I
LEAK
LEAK
LEAK
LEAK
CC
CC
IN
IN
I
I
I
I
LEAK
LEAK
LEAK
LEAK
R
R
U
SOURCE
SOURCE
R
R
R
R
SW
SW
SW
SW
20k
20k
20k
20k
+
(TYP)
(TYP)
(TYP)
(TYP)
and IN
U
C
C
IN
IN
Figure 18. LTC2415/LTC2415-1 Equivalent Analog Input Circuit
–
SWITCHING FREQUENCY
f
(F
f
(F
f
pins as a result of the
SW
SW
SW
O
O
W
C
C
= LOW OR HIGH)
= LOW)
= 76800Hz INTERNAL
= 69900Hz INTERNAL
= 0.5 • f
PAR
PAR
20pF
20pF
OSCILLATOR (LTC2415)
OSCILLATOR (LTC2415-1)
+
C
18pF
(TYP)
and IN
EQ
EOSC
PAR
IN
IN
LTC2415-1
LTC2415/
+
–
EXTERNAL OSCILLATOR
–
U
capacitor
2415 F19
IN
2415 F18
Figure 20. +FS Error vs R
Figure 21. –FS Error vs R
I IN
I IN
I REF
I REF
where
V
V
V
V
R
R
R
R
REF
REFCM
IN
INCM
EQ
EQ
EQ
EQ
IN
AVG
AVG
: :
3 61
4 32
3 97
REF
0 555 10
AVG
.
.
.
AVG
.
–10
–20
–30
–40
–50
IN
M
M
M M
50
40
30
20
10
REF
IN
0
V
0
IN
V
1 5
2
1
1
IN
REF
.
INTERNAL OSCILLATOR
IN
INTERNAL OSCILLATOR
1 5
INTERNAL OSCILLATOR
.
12
V
2
V
REF
REF
IN
IN
F
T
LTC2415/LTC2415-1
V
REF
REF
IN
IN
F
T
0 5
INCM
O
0 5
V
REF
O
CC
A
.
CC
A
V
REF
+
–
INCM
.
+
–
V
/
= GND
= 25 C
= GND
= 25 C
+
= GND
= 2.5V
REF
f
+
= 5V
= 2.5V
–
–
= 5V
EOSC
= 5V
R
10
0 5
10
C
= 5V
C
= 5V
= GND
R
= GND
0 5
EQ
.
C
C
IN
IN
V
EQ
.
C
C
V
IN
IN
REFCM
IN
INCM
IN
EXTERNAL OSCILLATOR
= 0.001 F
V
= 0.001 F
V
C
R
C
REFCM
= 0.01 F
INCM
= 0.01 F
R
IN
EQ
= 100pF
= 100pF
IN
EQ
= 0pF
100
R
= 0pF
100
R
SOURCE
SOURCE
SOURCE
SOURCE
V
REFCM
V
REFCM
60
50
50
( )
( )
1k
1k
Hz Notch F
Hz Notch F
at IN
Hz
at IN
V
REF
V
/
REF
V
60
IN
2
V
Hz Notch F
+
+
R
IN
2
10k
10k
EQ
R
or IN
or IN
EQ
O
O
2415 F21
2415 F20
LOW
HIGH
–
–
100k
100k
O
(Small C
(Small C
LTC2415
LOW
LTC2415
sn2415 24151fs
27
LTC2415 -1
IN
IN
)
)