Datasheet

LTC2444/LTC2445/
LTC2448/LTC2449
26
2444589fc
For more information www.linear.com/LTC2444
Table 8. Performance vs Oversample Ratio
OVER-
SAMPLE
RATIO
(OSR)
*RMS
NOISE
LTC2444/
LTC2448
*RMS
NOISE
LTC2445/
LTC2449
ENOB
(V
REF
= 5V)
MAXIMUM CONVERSION
RATE (sps)
FIRST NOTCH
FREQUENCY (Hz)
EFFECTIVE
NOISE BW (Hz)
–3dB POINT (Hz)
LTC2444
LTC2449
LTC2445/
LTC2449
Internal
Clock
External f
O
(1X Mode)
[f
O
/x]
External f
O
(2X Mode)
[f
O
/x]
Internal
Clock
External f
O
[f
O
/x]
Internal
9MHz
Clock
External f
O
[f
O
/x]
Internal
Clock
External f
O
[f
O
/x]
64 23µV 23µV 17 17 2816.35 f
ø
/2738 f
o
/1458 28125 f
o
/320 3148 f
o
/2860 1696 f
o
/5310
128 4.5µV 3.5µV 20.1 20 1455.49 f
o
/5298 f
o
/2738 14062.5 f
o
/640 1574 f
o
/5720 848 f
o
/10600
256 2.8µV 2µV 20.8 21.3 740.18 f
o
/10418 f
o
/5298 7031.3 f
o
/1280 787 f
o
/11440 424 f
o
/21200
512 2µV 1.4µV 21.3 21.8 373.28 f
o
/20658 f
o
/10418 3515.6 f
o
/2560 394 f
o
/22840 212 f
o
/42500
1024 1.4µV 1µV 21.8 22.4 187.45 f
o
/41138 f
o
/20658 1757.8 f
o
/5120 197 f
o
/45690 106 f
o
/84900
2048 1.1µV 750nV 22.1 22.9 93.93 f
o
/82098 f
o
/41138 878.9 f
o
/10200 98.4 f
o
/91460 53 f
o
/170000
4096 720nV 510nV 22.7 23.4 47.01 f
o
/164018 f
o
/82098 439.5 f
o
/20500 49.2 f
o
/183000 26.5 f
o
/340000
8192 530nV 375nV 23.2 24 23.52 f
o
/327858 f
o
/164018 219.7 f
o
/41000 24.6 f
o
/366000 13.2 f
o
/679000
16384 350nV 250nV 23.8 24.4 11.76 f
o
/655538 f
o
/327858 109.9 f
o
/81900 12.4 f
o
/731000 6.6 f
o
/1358000
32768 280nV 200nV 24.1 24.6 5.88 f
o
/1310898 f
o
/655538 54.9 f
o
/163800 6.2 f
o
/1463000 3.3 f
o
/2717000
*ADC noise increases by approximately √2 when OSR is decreased by a factor of 2 for OSR 32768 to OSR 256. The ADC noise at OSR 128 and OSR 64
include effects from internal modulator quantization noise.
and rejection characteristics. The digital filter’s response
can be adjusted by setting the oversample ratio (OSR)
through the SPI interface or by supplying an external
conversion clock to the F
O
pin.
Table 8 lists the properties of the LTC2444/LTC2445/
LTC2448/LTC2449 with various combinations of overs
-
ample ratio and clock frequency. Understanding these
properties is the key to fine tuning the characteristics of the
LTC2444/LTC2445/LTC2448/LTC2449 to the application.
Maximum Conversion Rate
The maximum conversion rate is the fastest possible rate
at which conversions can be performed.
First Notch Frequency
This is the first notch in the SINC
4
portion of the digital filter
and depends on the F
O
clock frequency and the oversample
ratio. Rejection at this frequency and its multiples (up to
the modulator sample rate of 1.8MHz) exceeds 120dB.
This is 8 times the maximum conversion rate.
applicaTions inForMaTion
28 2
29
38
37
8
9
36
3
2444589 F17
35
1,4,5,6,31,32,33,39
REFERENCE
VOLTAGE
0.1V TO V
CC
ANALOG INPUT
–0.5V
REF
TO
0.5V
REF
3-WIRE
SPI INTERFACE
4.5V TO 5.5V
30
V
CC
BUSY
f
O
REF
+
SCK
CH0
CH1
SDO
GND
CS
EXT
LTC2448
REF
–
1µF
0.1µF
LTC1799
OUT
DIV SET
GND
V
+
R
SET
NC
•
•
•
Figure 17. Simple External Clock Source