Datasheet

LTC2413
25
sn2413 2413fs
APPLICATIO S I FOR ATIO
WUU
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The effect of this input dynamic current can be analyzed
using the test circuit of Figure 17. The C
PAR
capacitor
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
IN
+ C
PAR
) closer to 5pF
thus achieving better performance than the one predicted
by Figures 18 and 19. For simplicity, two distinct situa-
tions can be considered.
Figure 16. LTC2413 Equivalent Analog Input Circuit
Figure 17. An RC Network at IN
+
and IN
–
Figure 19. –FS Error vs R
SOURCE
at IN
+
or IN
–
(Small C
IN
)Figure 18. +FS Error vs R
SOURCE
at IN
+
or IN
–
(Small C
IN
)
IIN
VV V
R
IIN
VV V
R
I REF
VV V
R
V
VR
I REF
VV V
R
V
VR
where
AVG
IN INCM REFCM
EQ
AVG
IN INCM REFCM
EQ
AVG
REF INCM REFCM
EQ
IN
REF EQ
AVG
REF INCM REFCM
EQ
IN
REF EQ
+
−
+
−
()
=
+−
•
()
=
−+ −
•
()
=
•− +
•
−
•
()
=
−• − +
•
+
•
05
05
15
05
15
05
2
2
.
.
.
.
.
.
::
.
./
V REF REF
V
REF REF
VININ
V
IN IN
R M INTERNAL OSCILLATOR
R f EXTERNAL OSCILLATOR
REF
REFCM
IN
INCM
EQ
EQ EOSC
=−
=
+






=−
=
−






=
=•
()
+−
+−
+−
+−
2
2
397
0 555 10
12
Ω
V
REF
+
V
IN
+
V
CC
R
SW
(TYP)
20k
I
LEAK
I
LEAK
V
CC
I
LEAK
I
LEAK
V
CC
R
SW
(TYP)
20k
C
EQ
18pF
(TYP)
R
SW
(TYP)
20k
I
LEAK
I
IN
+
V
IN
–
I
IN
–
I
REF
+
I
REF
–
2413 F16
I
LEAK
V
CC
I
LEAK
I
LEAK
SWITCHING FREQUENCY
f
SW
= 69900Hz INTERNAL OSCILLATOR
f
SW
= 0.5 • f
EOSC
EXTERNAL OSCILLATOR
V
REF
–
R
SW
(TYP)
20k
C
IN
2413 F17
V
INCM
+ 0.5V
IN
R
SOURCE
IN
+
LTC2413
C
PAR
≅20pF
C
IN
V
INCM
– 0.5V
IN
R
SOURCE
IN
–
C
PAR
≅20pF
R
SOURCE
(Ω)
1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05
+FS ERROR (ppm OF V
REF
)
2413 F18
50
40
30
20
10
0
V
CC
= 5V
REF
+
= 5V
REF
–
= GND
IN
+
= 5V
IN
–
= 2.5V
F
O
= GND
T
A
= 25°C
C
IN
= 0.01µF
C
IN
= 0.001µF
C
IN
= 100pF
C
IN
= 0pF
R
SOURCE
(Ω)
1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05
–FS ERROR (ppm OF V
REF
)
2413 F19
0
–10
–20
–30
–40
–50
V
CC
= 5V
REF
+
= 5V
REF
–
= GND
IN
+
= GND
IN
–
= 2.5V
F
O
= GND
T
A
= 25°C
C
IN
= 0.01µF
C
IN
= 0.001µF
C
IN
= 100pF
C
IN
= 0pF