LTC2411 LINER [Linear Technology], LTC2411 Datasheet - Page 29

• Manufacturer Part Number: LTC2411
• Description: 24-Bit No Latency ADC with Differential Input and Reference in MSOP
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
the internal oscillator is used, the 3dB input bandwidth of
the LTC2411 is 3.63Hz for 60Hz notch frequency (F
LOW) and 3.02Hz for 50Hz notch frequency (F
The 3dB input bandwidth for the LTC2411-1 is 3.30Hz
(F
frequency f
bandwidth is 0.236 • 10
Due to the complex filtering and calibration algorithms
utilized, the converter input bandwidth is not modeled very
accurately by a first order filter with the pole located at the
3dB frequency. When the internal oscillator is used, the
shape of the LTC2411/LTC2411-1 input bandwidth is
shown in Figure 28. When an external oscillator of fre-
quency f
input bandwidth can be derived from Figure 28, F
curve of the LTC2411 in which the horizontal axis is scaled
by f
The conversion noise (1.45 V
can be modeled as a white noise source connected to a
noise free converter. The noise spectral density is 70nV/ Hz
for an infinite bandwidth source and 126nV/ Hz for a
single 0.5MHz pole source. From these numbers, it is clear
that particular attention must be given to the design of
external amplification circuits. Such circuits face the
simultaneous requirements of very low bandwidth (just a
few Hz) in order to reduce the output referred noise and
relatively high bandwidth (at least 500kHz) necessary to
drive the input switched-capacitor network. A possible
O
EOSC
= LOW). If an external conversion clock generator of
EOSC
/153600.
Figure 26. Resolution (Noise
vs Output Data Rate and Reference Voltage
22
20
19
18
21
EOSC
is used, the shape of the LTC2411/LTC2411-1
0
V
REF
V
V
F
RES = LOG
T
O
A
CC
INCM
IN
10
= EXT OSC
= 25 C
OUTPUT DATA RATE (READINGS/SEC)
is connected to the F
= 0V
–
= 5V
= GND
= 2.5V
20
U
2
30
(V
REF
–6
40 50
/NOISE
U
V
V
• f
REF
REF
EOSC
= 2.5V
= 5V
RMS
RMS
60
)
70
.
W
RMS
typical for V
80
O
pin, the 3dB input
90
2411 F26
1LSB)
100
O
U
REF
= HIGH).
O
= LOW
= 5V)
O
=
solution is a high gain, low bandwidth amplifier stage
followed by a high bandwidth unity-gain buffer.
When external amplifiers are driving the LTC2411/
LTC2411-1, the ADC input referred system noise calcula-
tion can be simplified by Figure 29. The noise of an
amplifier driving the LTC2411/LTC2411-1 input pin can be
modeled as a band-limited white noise source. Its band-
width can be approximated by the bandwidth of a single
pole lowpass filter with a corner frequency f
noise spectral density is n
x-axis selector, we can find on the y-axis the noise equiva-
lent bandwidth freq
bandwidth includes the band limiting effects of the ADC
Figure 27. Resolution (INL
vs Output Data Rate and Reference Voltage
–0.5
–1.0
–1.5
–2.0
–2.5
–3.0
–3.5
–4.0
–4.5
–5.0
–5.5
–6.0
22
20
18
16
14
12
10
0.0
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
Figure 28. Input Signal Bandwidth
Using the Internal Oscillator
V
REF
V
V
F
RES = LOG
T
O
A
CC
INCM
IN
10
= EXT OSC
= 25 C
OUTPUT DATA RATE (READINGS/SEC)
= 0V
–
LTC2411/LTC2411-1
= 5V
= GND
= 2.5V
20
i
2
30
(V
of the input driving amplifier. This
REF
(LTC2411-1)
F
(LTC2411)
V
O
40
F
REF
/INL
= HIGH
O
i
. From Figure 29, using f
= LOW
= 2.5V
50
MAX
)
60
MAX
70
V
REF
F
(LTC2411)
80
O
= LOW
1LSB)
= 5V
90
2411 F27
2411 F28
100
i
. The amplifier
29
i
as the