LTC1417 LINER [Linear Technology], LTC1417 Datasheet - Page 12

• Manufacturer Part Number: LTC1417
• Description: Low Power 14-Bit, 400ksps Sampling ADC Converter with Serial I/O
• Manufacturer: LINER [Linear Technology]

APPLICATIONS
LTC1417
Choosing an Input Amplifier
Choosing an input amplifier is easy if a few requirements
are taken into consideration. First, choose an amplifier that
has a low output impedance (<100 ) at the closed-loop
bandwidth frequency. For example, if an amplifier is used
in a gain of 1 and has a closed-loop bandwidth of 10MHz,
then the output impedance at 10MHz must be less than
100 . The second requirement is that the closed-loop
bandwidth must be greater than 10MHz to ensure ad-
equate small-signal settling for full throughput rate. If
slower op amps are used, more settling time can be
provided by increasing the time between conversions.
The best choice for an op amp to drive the LTC1417 will
depend on the application. Generally, applications fall into
two categories: AC applications where dynamic specifica-
tions are most critical and time domain applications where
DC accuracy and settling time are most critical. The
following list is a summary of the op amps that are suitable
for driving the LTC1417. More detailed information is
available in the Linear Technology Databooks and on the
LinearView
LT
supply current. Good AC and DC specifications. Suitable
for dual supply application.
LT1357: 25MHz, 600V/ s Op Amp. 2.5mA maximum
supply current. Good AC and DC specifications. Suitable
for dual supply application.
LinearView is a trademark of Linear Technology Corporation.
12
®
1354: 12MHz, 400V/ s Op Amp. 1.25mA maximum
0.01
100
0.1
10
TM
1
1
Figure 7. t
CD-ROM.
10
U
SOURCE RESISTANCE ( )
ACQ
100
INFORMATION
vs Source Resistance
U
1k
W
10k
1417 F07
100k
U
LT1360: 50MHz Voltage Feedback Amplifier. 3.8mA sup-
ply current, 2.5V to 15V supplies. High A
offset and 80ns settling to 1mV (4V step, inverting and
noninverting configurations) make it suitable for fast DC
applications. Excellent AC specifications. Dual and quad
versions are available as LT1361 and LT1362.
LT1468: 90MHz Voltage Feedback Amplifier. 5V to 15V
supplies. Lower distortion and noise. Settles to 0.01% in
770ns. Distortion is –115dB to 20kHz.
LT1498/LT1499: 10MHz, 6V/ s, Dual/Quad Rail-to-Rail
Input and Output Op Amps. 1.7mA supply current per
amplifier. 2.2V to 15V supplies. Good AC performance,
input noise voltage = 12nV/ Hz (typ).
LT1630/LT1631: 30MHz, 10V/ s, Dual/Quad Rail-to-Rail
Input and Output Precision Op Amps. 3.5mA supply
current per amplifier. 2.7V to 15V supplies. Best AC
performance, input noise voltage = 6nV/ Hz (typ),
THD = – 86dB at 100kHz.
LT1813: Dual 100MHz 750V/ s 3mA VFA. 5V to 5V
supplies. Distortion is – 86dB to 100kHz and – 77dB to
1MHz with 5V supplies (2V
fast AC applications with 5V supplies.
Input Filtering
The noise and the distortion of the input amplifier and
other circuitry must be considered since they will add to
the LTC1417 noise and distortion. The small-signal band-
width of the sample-and-hold circuit is 10MHz. Any noise
or distortion products that are present at the analog inputs
will be summed over this entire bandwidth. Noisy input
circuitry should be filtered prior to the analog inputs to
minimize noise. A simple 1-pole RC filter is sufficient for
many applications. For example, Figure 8 shows a 1000pF
ANALOG INPUT
Figure 8. RC Input Filter
100
10 F
1000pF
P-P
into 500 ). Great part for
1
2
3
4
5
A
A
V
REFCOMP
AGND
IN
IN
REF
+
–
LTC1417
1417 F08
VOL
, 1mV