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LTC2446/LTC2447
1
24467fa
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
■
Flow
■
Weight Scales
■
Pressure
■
Direct Temperature Measurement
■
Gas Chromatography
■
Five Selectable Differential Reference Inputs
■
Four Differential/Eight Single-Ended Inputs
■
4-Way MUX for Multiple Ratiometric
Measurements
■
Up to 8kHz Output Rate
■
Up to 4kHz Multiplexing Rate
■
Selectable Speed/Resolution:
2µV
RMS
Noise at 1.76kHz Output Rate
200nV
RMS
Noise at 13.8Hz Output Rate with
Simultaneous 50/60Hz Rejection
■
Guaranteed Modulator Stability and Lock-Up
Immunity for any Input and Reference Conditions
■
0.0005% INL, No Missing Codes
■
Autosleep Enables 20µA Operation at 6.9Hz
■
<5µV Offset (4.5V < V
CC
< 5.5V, – 40°C to 85°C)
■
Differential Input and Differential Reference with
GND to V
CC
Common Mode Range
■
No Latency Mode, Each Conversion is Accurate Even
After a New Channel is Selected
■
Internal Oscillator—No External Components
■
LTC2447 Includes MUXOUT/ADCIN for External
Buffering or Gain
■
Tiny QFN 5mm x 7mm Package
24-Bit High Speed
8-Channel ∆Σ ADCs with
Selectable Multiple Reference Inputs
The LTC
®
2446/LTC2447 4-terminal switching enables
multiplexed ratiometric measurements. Four sets of se-
lectable differential inputs coupled with four sets of differ-
ential reference inputs allow multiple RTDs, bridges and
other sensors to be digitized by a single converter. A fifth
differential reference input can be selected for any input
channel not requiring ratiometric measurements (ther-
mocouples, voltages, current sense, etc.). The flexible
input multiplexer allows single-ended or differential in-
puts coupled with a slaved reference input or a universal
reference input.
A proprietary delta-sigma architecture results in absolute
accuracy (offset, full-scale, linearity) of 15ppm, noise as
low as 200nV
RMS
and speeds as high as 8kHz. Through a
simple 4-wire interface, ten speed/resolution combina-
tions can be selected. The first conversion following a
speed, resolution, channel change or reference change is
valid since there is no settling time between conversions,
enabling scan rates of up to 4kHz. Additionally, a 2x mode
can be selected for any speed-enabling output rates up to
8kHz with one cycle of latency.
, LTC and LT are registered trademarks of Linear Technology Corporation.
LTC2446 Speed vs RMS Noise
Multiple Ratiometric Measurement System
CONVERSION RATE (Hz)
1
0.1
RMS NOISE (µV)
1
10
100
10 100
24467 TA02
1000 10000
2.8µV AT 880Hz
280nV AT 6.9Hz
(50/60Hz REJECTION)
V
CC
= 5V
V
REF
= 5V
V
IN
+
= V
IN
–
= 0V
2x SPEED MODE
NO LATENCY MODE
VARIABLE SPEED/
RESOLUTION 24-BIT
∆Σ ADC
+
–
19-INPUT
4-OUTPUT
MUX
•
•
•
REF
+
V
CC
LTC2446
IN
+
IN
–
REF
–
CS
SDI
SDO
SCK
24467 TA01
Protected by U.S. Patents, including 6140950, 6169506, 6208279, 6411242, 6639526
