LTC1416 Linear Technology, LTC1416 Datasheet - Page 11

• Manufacturer Part Number: LTC1416
• Description: Low Power 14-Bit/ 400ksps Sampling ADC
• Manufacturer: Linear Technology

APPLICATIONS
Input Range
The 2.5V input range of the LTC1416 is optimized for low
noise and low distortion. Most op amps also perform best
over this same range, allowing direct coupling to the
analog inputs and eliminating the need for special transla-
tion circuitry.
Some applications may require other input ranges. The
LTC1416 differential inputs and reference circuitry can
Input Filtering
The noise and the distortion of the input amplifier and
other circuitry must be considered since they will add to
the LTC1416 noise and distortion. The small-signal band-
width of the sample-and-hold circuit is 15MHz. 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 7 shows a 1000pF
capacitor from A
to limit the input bandwidth to 800kHz. The 1000pF
capacitor also acts as a charge reservoir for the input
sample-and-hold and isolates the ADC input from sam-
pling glitch sensitive circuitry. High quality capacitors and
resistors should be used since these components can add
distortion. NPO and silver mica type dielectric capacitors
have excellent linearity. Carbon surface mount resistors
can also generate distortion from self-heating and from
damage that may occur during soldering. Metal film
surface mount resistors are much less susceptible to both
problems.
ANALOG
INPUT
200
Figure 7. RC Input Filter
IN
+
U
to ground and a 200 source resistor
1000pF
22 F
INFORMATION
U
1
2
3
4
5
A
A
V
REFCOMP
AGND
IN
IN
REF
+
–
LTC1416
W
1416 F07
U
accommodate other input ranges often with little or no
additional circuitry. The following sections describe the
reference and input circuitry and how they affect the input
range.
Internal Reference
The LTC1416 has an on-chip, temperature compensated,
curvature corrected, bandgap reference that is factory
trimmed to 2.500V. It is connected internally to a reference
amplifier and is available at V
4k resistor is in series with the output so that it can be
easily overdriven by an external reference or other cir-
cuitry (see Figure 8b). The reference amplifier gains the
voltage at the V
internal reference voltage. This provides buffering be-
tween the V
22 F
4.0625V
2.5V
Figure 8b. Using the LT1019-2.5 as an External Reference
3
4
5
LT1019A-2.5
V
REFCOMP
AGND
REF
REF
Figure 8a. LTC1416 Reference Circuit
V
5V
IN
pin and the high speed capacitive DAC. The
V
REF
OUT
pin by 1.625 to create the required
22 F
128k
ANALOG
80k
R2
R3
INPUT
AMP
REF
REF
1
2
3
4
5
A
A
V
REFCOMP
AGND
(Pin 3). See Figure 8a. A
IN
IN
REF
+
–
R1
4k
LTC1416
LTC1416
REFERENCE
LTC1416
BANDGAP
1416 F08b
11
1416 F08a