24-Bit 2Msps SAR ADC

24-Bit 2Msps SAR ADC
145dB Dynamic Range
Digital Averaging Filter Simplifies Interfacing to µProcessors
The LTC ®2380-24 is a breakthrough no-latency 24-bit 2Msps SAR ADC. An integrated digital filter reduces noise to achieve
true 24-bit dynamic range. The LTC2380-24 features a unique digital interface, enabling results to be read with a slow serial
clock, easing interfacing to microprocessors. The DC histogram measured with an output data rate of 30.5sps (65536
averages) shows less than 1LSBRMS transition noise. The LTC2380-24 targets industrial and instrumentation applications
requiring high dynamic range.
Features
nn
nn
nn
nn
nn
nn
nn
nn
nn
Guaranteed 24-Bit No Missing Codes
Integrated Digital Filter
101dB Dynamic Range (Typ) at 1.5Msps
145dB Dynamic Range (Typ) at 30.5sps
±0.5ppm INL (Typ)
−117dB THD (Typ) at fIN = 2kHz
Low Power: 28mW at 2Msps
50Hz/60Hz Rejection
Single 2.5V Supply
16-Lead MSOP and 4mm × 3mm DFN Packages
1Msps
24-Bit
with Integrated
Digital Filter
20-Bit
Fully Differential
100dB SNR at 1.5Msps
DC Histogram
200nVRMS Noise @ 30.5sps
10000
8000
COUNTS
nn
2Msps
2380-24
Pseudo-Differential
98dB SNR at 1Msps
2368-24
Fully Differential
104dB SNR at 1Msps
2378-20
L, LT, LTC, LTM, Linear Technology and the Linear logo are
registered trademarks and Linduino, PScope and QuikEval
are trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
6000
4000
2000
0
–1
0
24-BIT CODES
1
Digital Filter Requires No Programming or Configuration
The digital filter inside the LTC2380-24 automatically averages N consecutive conversion results until the filter output is read
from the device. When the filter output result is read, the digital filter is reset and a new averaging operation starts with the next
conversion result. An optional distributed read operation lowers the serial data clock’s rate to as low as one clock per sample.
With the distributed read operation, the maximum sampling rate increases to 2Msps.
Example of Reading Data with No Averaging
Max fSMPL = 1.5Msps
CNV
BUSY
24 SCKs
SCK
24 SCKs
24 SCKs
24 SCKs
24 SCKs
24 SCKs
Reading all 24 bits in one cycle
results in no averaging and no
latency
SDO
Example of Averaging Four Samples Using Distributed Read
Max fSMPL = 2Msps
CNV
BUSY
8 SCKs
SCK
8 SCKs
8 SCKs
8 SCKs
Distributing the read operation
over three ADC cycles to average
four samples and slow down the
serial interface
AVERAGE OF 4 CONVERSION RESULTS
SDO
Example of Averaging 25 Samples Using Distributed Read
Max fSMPL = 2Msps
CNV
BUSY
SCK
SDO
24
1
25
1 SCK
2
1 SCK
24
1 SCK
AVERAGE OF 25 CONVERSION RESULTS
25
1 SCK
Distributing the read operation
over 24 ADC cycles to average
25 samples and run the serial
interface as slow as 2MHz
Reject Particular Input Frequencies
The LTC2380-24’s integrated digital filter exhibits a sinc1 function which allows the rejection of a particular input frequency
or a combination of frequencies and their harmonics. This is done by selecting the appropriate number of averages, N, based
on the sampling rate, fSMPL, and the desired frequency to be rejected, fREJECT. N is then given by
N=
fSMPL
f
REJECT
For example, the rejection of 50Hz and 60Hz with their harmonics is desired in a large number of applications. Setting
fREJECT = 10Hz (of which 50Hz and 60Hz are multiples) and f SMPL = 10.24ksps, results in N = 1024 averages. The
frequency response of the digital filter using these settings is shown below.
50Hz/60Hz Rejection Example
0
–10
GAIN (dB)
–20
–30
–40
–50
–60
0
10
20
30
40
50
60
70
80
90
FREQUENCY (Hz)
100
110
120
130
140
150
Excellent Rejection at 50Hz, 60Hz and Their Harmonics
Dynamic Range vs Output Data Rate
The digital filter can average 1 to 65536 conversion results in real time. This dramatically improves the dynamic range from
101dB at 1.5Msps to 145dB at an output data rate of 30.5sps, achieving true 24-bit performance.
150.00
DYNAMIC RANGE (dB)
140.00
130.00
120.00
110.00
100.00
90.00
10
100
1000
10,000
OUTPUT DATA RATE (sps)
100,000
1,000,000
Easy-to-Use Evaluation System
Evaluating the LTC2380-24 is made easy with the DC2289 demonstration board. The DC2289 demonstrates correct layout and
recommended device selection to achieve the highest performance design. Connect the DC2289 to the DC590 or DC2026
QuikEvalTM and DC890 PScopeTM data collection boards for use with our free data acquisition and analysis tools.
QuikEval
Use the QuikEval system with the DC590 or the DC2026 LinduinoTM One controller board to demonstrate DC performance such
as peak-to-peak noise and DC linearity for any selected number of averages. The DC2026 can also be used to evaluate the
provided C++ code libraries, saving design time.
PScope
Use the PScope data collection system with the DC890 to achieve precise sampling rates or to demonstrate AC performance
such as SNR, THD, SINAD and SFDR.
www.linear.com/2380-24 n 1-800-4-LINEAR
1015
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