LTC2446 Datasheet, PDF (1/28 Pages) Linear Technology – 24-Bit High Speed 8-Channel ΔΣ ADCs with Selectable Multiple Reference Inputs

LTC2446/LTC2447
24-Bit High Speed
8-Channel ∆Σ ADCs with
Selectable Multiple Reference Inputs
FEATURES
■ _{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 < VCC < 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}
U
APPLICATIO S
■ _Flow
■ _{Weight Scales}
■ _Pressure
■ _{Direct Temperature Measurement}
■ _{Gas Chromatography}
DESCRIPTIO
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.
Protected by U.S. Patents, including 6140950, 6169506, 6208279, 6411242, 6639526
TYPICAL APPLICATIO
Multiple Ratiometric Measurement System
V_CC
REF⁺
LTC2446
•
•
•
IN⁺
19-INPUT
4-OUTPUT
+
VARIABLE SPEED/
RESOLUTION 24-BIT
CS
SDI
MUX _IN–
–
∆Σ ADC
SDO
SCK
REF^–
24467 TA01
LTC2446 Speed vs RMS Noise
100
V_CC = 5V
VV_RINE+F
=
=
5V
V_IN–
=
0V
2x SPEED MODE
NO LATENCY MODE
10
2.8µV AT 880Hz
280nV AT 6.9Hz
1 ^{(50/60Hz REJECTION)}
0.1
1
10
100
1000
CONVERSION RATE (Hz)
10000
24467 TA02
24467fa
1