LTC2445_15 Datasheet, PDF (1/28 Pages) Linear Technology – 24-Bit High Speed 8-/16-Channel ADCs with Selectable Speed/Resolution

LTC2444/LTC2445/
LTC2448/LTC2449
24-Bit High Speed
8-/16-Channel ∆Σ ADCs with
Selectable Speed/Resolution
FEATURES
■ _{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)}
■ _{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}
■ _{LTC2445/LTC2449 Include MUXOUT/ADCIN for}
External Buffering or Gain
■ _{Tiny QFN 5mm xU7mm Package}
APPLICATIO S
■ _{High Speed Multiplexing}
■ _{Weight Scales}
■ _{Auto Ranging 6-Digit DVMs}
■ _{Direct Temperature Measurement}
■ _{High Speed Data Acquisition}
DESCRIPTIO
The LTC^®2444/LTC2445/LTC2448/LTC2449 are 8-/16-
channel (4-/8-differential) high speed 24-bit No Latency
∆Σ^TM 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/280nV_RMS to 3.5kHz/25µV_RMS (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.
Any combination of single-ended or differential inputs can
be selected with a common mode input range from ground
to V_CC, independent of V_REF. 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No Latency ∆Σ is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
THERMOCOUPLE
Simple 24-Bit Variable Speed Data Acquisition System
4.5V TO 5.5V
CH0
CH1
•
•
•
CH7
CH8
•
•
•
CH15
COM
16-CHANNEL
MUX
REF⁺ V_CC
F_O
+
VARIABLE SPEED/
RESOLUTION
SDI
SCK
– ^DIFFERENTIAL
SDO
24-BIT ∆Σ ADC
CS
1µF
= EXTERNAL OSCILLATOR
= INTERNAL OSCILLATOR
(SIMULTANEOUS 50Hz/60Hz
REJECTION AT 6.9Hz OUTPUT RATE)
4-WIRE
SPI INTERFACE
REF ^–
GND
LTC2448
2444 TA01
LTC2444/LTC2448
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
2440 TA02
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