LTC2444/LTC2445/
LTC2448/LTC2449
24-Bit High Speed
8-/16-Channel ∆Σ ADCs with
Selectable Speed/Resolution
U
FEATURES
DESCRIPTIO
The LTC®2444/LTC2445/LTC2448/LTC2449 are 8-/16-
channel (4-/8-differential) high speed 24-bit No Latency
∆ΣTM ADCs. They use a proprietary delta-sigma architec-
ture enabling variable speed/resolution. Through a simple
4-wire serial interface, ten speed/resolution combinations
6.9Hz/280nVRMS to 3.5kHz/25µVRMS (4kHz with external
oscillator) can be selected with no latency between con-
version results or shift in DC accuracy (offset, full-scale,
linearity, drift). Additionally, a 2X speed mode can be
selected enabling output rates up to 7kHz (8kHz if an
external oscillator is used) with one cycle latency.
■
Up to 8 Differential or 16 Single-Ended Input
Channels
■
Up to 8kHz Output Rate
■
Up to 4kHz Multiplexing Rate
■
Selectable Speed/Resolution
■
2µVRMS Noise at 1.76kHz Output Rate
■
200nVRMS 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)
Any combination of single-ended or differential inputs can
beselectedwithacommonmodeinputrangefromground
to VCC, independent of VREF. While operating in the 1X
speed mode the first conversion following a new speed,
resolution, or channel selection is valid. Since there is no
settling time between conversions, all 8 differential chan-
nels can be scanned at a rate of 500Hz. At the conclusion
of each conversion, the converter is internally reset elimi-
nating any memory effects between successive conver-
sions and assuring stability of the high order delta-sigma
modulator.
■
Differential Input and Differential Reference with
GND to VCC Common Mode Range
■
No Latency Mode, Each Conversion is Accurate Even
After a New Channel is Selected
■
Internal Oscillator—No External Components
■
LTC2445/LTC2449 Include MUXOUT/ADCIN for
External Buffering or Gain
■
Tiny QFN 5mm xU7mm Package
APPLICATIO S
■
High Speed Multiplexing
■
Weight Scales
, LTC and LT are registered trademarks of Linear Technology Corporation.
No Latency ∆Σ is a trademark of Linear Technology Corporation.
■
Auto Ranging 6-Digit DVMs
■
Direct Temperature Measurement
■
High Speed Data Acquisition
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TYPICAL APPLICATIO
LTC2444/LTC2448
Simple 24-Bit Variable Speed Data Acquisition System
Speed vs RMS Noise
4.5V TO 5.5V
100
10
1
V
V
V
= 5V
CC
= 5V
IN
REF
1µF
+
–
= V = 0V
IN
+
REF
V
2X SPEED MODE
CC
CH0
CH1
= EXTERNAL OSCILLATOR
NO LATENCY MODE
= INTERNAL OSCILLATOR
F
O
(SIMULTANEOUS 50Hz/60Hz
REJECTION AT 6.9Hz OUTPUT RATE)
•
•
•
2.8µV AT 880Hz
CH7
CH8
SDI
SCK
SDO
CS
16-CHANNEL
MUX
VARIABLE SPEED/
RESOLUTION
DIFFERENTIAL
24-BIT ∆Σ ADC
280nV AT 6.9Hz
(50/60Hz REJECTION)
+
–
4-WIRE
SPI INTERFACE
THERMOCOUPLE
•
•
•
CH15
COM
0.1
–
REF
1
10
100
1000
10000
CONVERSION RATE (Hz)
GND
LTC2448
2440 TA02
2444 TA01
sn2444589 2444589fs
1