LTC2447IUHF#PBF Linear Technology, LTC2447IUHF#PBF Datasheet - Page 21

• Manufacturer Part Number: LTC2447IUHF#PBF
• Description: IC ADC 24BIT 8CH HI SPEED 38QFN
• Manufacturer: Linear Technology

Specifications of LTC2447IUHF#PBF

• Number Of Bits: 24
• Sampling Rate (per Second): 8k
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 40mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 38-WFQFN, Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIO S I FOR ATIO
Normal Mode Rejection and Antialiasing
One of the advantages delta-sigma ADCs offer over con-
ventional ADCs is on-chip digital filtering. Combined with
a large oversampling ratio, the LTC2446/LTC2447 signifi-
cantly simplify antialiasing filter requirements.
The LTC2446/LTC2447’s speed/resolution is determined
by the over sample ratio (OSR) of the on-chip digital filter.
The OSR ranges from 64 for 3.5kHz output rate to 32,768
for 6.9Hz (in 1x mode) output rate. The value of OSR and
the sample rate f
device. The first NULL of the digital filter is at f
multiples of f
6. The rejection at the frequency f
80dB, see Figure 11.
Figure 10. LTC2446/LTC2447
Normal Mode Rejection (Internal Oscillator)
Figure 11. LTC2446/LTC2447
Normal Mode Rejection (Internal Oscillator)
–120
–140
–100
–100
–110
–130
–140
–120
–20
–40
–60
–80
–80
–90
0
47
N
0
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
where f
S
49
determine the filter characteristics of the
U
60
51
N
SINC
= f
53
U
S
4
/OSR, see Figure 10 and Table
ENVELOPE
120
55
57
N
180
59
W
±14% is better than
24467 F10
61
24467 F11
240
63
U
N
and
Table 6. OSR vs Notch Frequency (f
Running at 9MHz)
*Simultaneous 50/60Hz rejection
If F
1.8MHz ±5% (over supply and temperature variations). At
an OSR of 32,768, the first NULL is at f
latency output rate is f
the noise performance of the device is 280nV
(LTC2446) and 200nV
80dB rejection of 50Hz ±2% and 60Hz ±2%. Since the OSR
is large (32,768) the wide band rejection is extremely large
and the antialiasing requirements are simple. The first
multiple of f
Figure 12.
The first NULL becomes f
(an output rate of 880Hz) and F
NULL has shifted, the sample rate remains constant. As a
result of constant modulator sampling rate, the linearity,
O
is grounded, f
Figure 12. LTC2446/LTC2447
Normal Mode Rejection (Internal Oscillator)
–100
–120
–140
–20
–40
–60
–80
0
32768*
16384
S
1024
2048
4096
8192
0
OSR
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
128
256
512
64
occurs at 55Hz • 32,768 = 1.8MHz, see
S
LTC2446/LTC2447
REJECTION > 120dB
N
is set by the on-chip oscillator at
RMS
/8 = 6.9Hz. At the maximum OSR,
N
1000000
= 7.04kHz with an OSR of 256
(LTC2447) with better than
N
) (with Internal Oscillator
O
1.8MHz
grounded. While the
N
24467 F12
NOTCH (f
= 55Hz and the no
28.16kHz
14.08kHz
7.04kHz
3.52kHz
1.76kHz
2000000
880Hz
440Hz
220Hz
110Hz
55Hz
N
)
21
24467fa
RMS