
LTC2446/LTC2447
23
24467fa
APPLICATIO S I FOR ATIO
WU
U
Figure 15. Versatile 4-Way Multiplexer Measures Multiple Ratiometric/Absolute Sensors
Figure 16. LTC2446 Input Structure
When using the internal oscillator, fSW is 1.8MHz and the
equivalent resistance is approximately 110k
.
Input Bandwidth and Frequency Rejection
The combined effect of the internal SINC4 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 fo 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.
VREFG
+
10
F
VREFO1
+
VREFO1
–
RTD
CH0
CH1
LTC2446
VREF
VCC
VREF23
+
VREF23
–
IN+
VARIABLE SPEED
RESOLUTION
24-BIT
Σ ADC
REF+
IN–
REF–
RTD
RATIOMETRIC
ABSOLUTE
vs VREFG
BRIDGE
CH2
CH3
VREF45
+
VREF45
–
CH4
CH5
COM
VREFG
24467 F15
CH6
CH7
CS
+
–
SDI
SDO
SCK
VREF+
VIN+
VCC
RSW (TYP)
500
ILEAK
VCC
ILEAK
VCC
RSW (TYP)
500
CEQ
5pF
(TYP)
(CEQ = 2pF
SAMPLE CAP
+ PARASITICS)
RSW (TYP)
500
ILEAK
IIN+
VIN–
IIN–
IREF+
IREF–
24467 F16
ILEAK
VCC
ILEAK
SWITCHING FREQUENCY
fSW = 1.8MHz INTERNAL OSCILLATOR
fSW = fEOSC/5 EXTERNAL OSCILLATOR
VREF–
RSW (TYP)
500
MUX