LTC2440
24-Bit High Speed
Differential Δ∑ ADC with
Selectable Speed/Resolution
DESCRIPTION
FEATURES
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Up to 3.5kHz Output Rate
Selectable Speed/Resolution
2μVRMS Noise at 880Hz Output Rate
200nVRMS Noise at 6.9Hz Output Rate with
Simultaneous 50/60Hz Rejection
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 VCC Common Mode Range
No Latency, Each Conversion is Accurate Even After
an Input Step
Internal Oscillator—No External Components
Pin Compatible with the LTC2410
24-Bit ADC in Narrow 16-Lead SSOP Package
APPLICATIONS
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High Speed Multiplexing
Weight Scales
Auto Ranging 6-Digit DVMs
Direct Temperature Measurement
High Speed Data Acquisition
The LTC®2440 is a high speed 24-bit No Latency Δ∑TM
ADC with 5ppm INL and 5μV offset. It uses proprietary
delta-sigma architecture enabling variable speed and resolution with no latency. Ten speed/resolution combinations
(6.9Hz/200nVRMS to 3.5kHz/25μVRMS) are programmed
through a simple serial interface. Alternatively, by tying a
single pin HIGH or LOW, a fast (880Hz/2μVRMS) or ultralow
noise (6.9Hz, 200nVRMS, 50/60Hz rejection) speed/resolution combination can be easily selected. The accuracy
(offset, full-scale, linearity, drift) and power dissipation
are independent of the speed selected. Since there is no
latency, a speed/resolution change may be made between
conversions with no degradation in performance.
Following each conversion cycle, the LTC2440 automatically enters a low power sleep state. Power dissipation
may be reduced by increasing the duration of this sleep
state. For example, running at the 3.5kHz conversion speed
but reading data at a 100Hz rate draws 240μA average
current (1.1mW) while reading data at a 7Hz output rate
draws only 25μA (125μW).The LTC2440 communicates
through a flexible 3-wire or 4-wire digital interface that is
compatible with the LTC2410 and is available in a narrow
16-lead SSOP package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
No Latency Δ∑ is a trademark of Linear Technology Corporation. All other trademarks are
the property of their respective owners.
TYPICAL APPLICATION
Speed vs RMS Noise
100
Simple 24-Bit 2-Speed Acquisition System
VCC = 5V
VREF = 5V
VIN+ = VIN– = 0V
VCC
REFERENCE VOLTAGE
0.1V TO VCC
ANALOG INPUT
–0.5VREF TO 0.5VREF
RMS NOISE (μV)
4.5V TO 5.5V
BUSY
LTC2440
fO
REF+
4
REF–
SCK
+
SDO
IN–
3-WIRE
SPI INTERFACE
CS
IN
EXT
2440 TA01
2μV AT 880Hz
200nV AT 6.9Hz
1 (50/60Hz REJECTION)
6.9Hz, 200nV NOISE,
50/60Hz REJECTION
10-SPEED SERIAL
PROGRAMMABLE
SDI
GND
VCC
10
880Hz OUTPUT RATE,
2μV NOISE
0.1
1
1000
10
100
CONVERSION RATE (Hz)
10000
2440 TA01
2440 TA02
2440fd
1