Datasheet

LTC2446/LTC2447
23
24467fa
APPLICATIO S I FOR ATIO
WUU
U
Figure 15. Versatile 4-Way Multiplexer Measures Multiple Ratiometric/Absolute Sensors
Figure 16. LTC2446 Input Structure
When using the internal oscillator, f
SW
is 1.8MHz and the
equivalent resistance is approximately 110kΩ.
Input Bandwidth and Frequency Rejection
The combined effect of the internal SINC
4
digital filter and
the digital and analog autocalibration circuits determines
the LTC2446/LTC2447 input bandwidth and rejection
characteristics. The digital filter’s response can be ad-
justed by setting the oversample ratio (OSR) through the
SPI interface or by supplying an external conversion clock
to the f
o
pin.
Table 7 lists the properties of the LTC2446/LTC2447 with
various combinations of oversample ratio and clock fre-
quency. Understanding these properties is the key to fine
tuning the characteristics of the LTC2446/LTC2447 to the
application.
V
REFG
+
10µF
V
REFO1
+
V
REFO1
–
RTD
CH0
CH1
LTC2446
V
REF
V
CC
V
REF23
+
V
REF23
–
IN
+
VARIABLE SPEED
RESOLUTION
24-BIT ∆Σ ADC
REF
+
IN
–
REF
–
RTD
RATIOMETRIC
ABSOLUTE
vs V
REFG
BRIDGE
CH2
CH3
V
REF45
+
V
REF45
–
CH4
CH5
COM
V
REFG
24467 F15
CH6
CH7
CS
+
–
SDI
SDO
SCK
V
REF
+
V
IN
+
V
CC
R
SW
(TYP)
500Ω
I
LEAK
I
LEAK
V
CC
I
LEAK
I
LEAK
V
CC
R
SW
(TYP)
500Ω
C
EQ
5pF
(TYP)
(C
EQ
= 2pF
SAMPLE CAP
+ PARASITICS)
R
SW
(TYP)
500Ω
I
LEAK
I
IN
+
V
IN
–
I
IN
–
I
REF
+
I
REF
–
24467 F16
I
LEAK
V
CC
I
LEAK
I
LEAK
SWITCHING FREQUENCY
f
SW
= 1.8MHz INTERNAL OSCILLATOR
f
SW
= f
EOSC
/5 EXTERNAL OSCILLATOR
V
REF
–
R
SW
(TYP)
500Ω
MUX
MUX