LTC2362 Linear Technology, LTC2362 Datasheet - Page 17

• Manufacturer Part Number: LTC2362
• Description: (LTC2360 - LTC2362) 12-Bit Serial ADCs
• Manufacturer: Linear Technology

Input Filtering and Source Impedance
The noise and the distortion of the input amplifi er and
other circuitry must be considered since they will add to
the LTC2360/LTC2361/LTC2362 noise and distortion. The
small-signal bandwidth of the sample-and-hold circuit is
10MHz. Any noise or distortion products that are pres-
ent at the analog inputs will be summed over this entire
bandwidth. Noisy input circuitry should be fi ltered prior
to the analog inputs to minimize noise. A simple 1-pole
RC fi lter is suffi cient for many applications. For example,
Figure 14 shows a 220pF capacitor from A
and a 51Ω source resistor to limit the input bandwidth
to 10MHz. The 220pF capacitor also acts as a charge
reservoir for the input sample-and-hold and isolates the
ADC input from sampling-glitch sensitive circuitry. High
quality capacitors and resistors should be used since these
components can add distortion. NPO and silvermica type
dielectric capacitors have excellent linearity. Carbon surface
mount resistors can generate distortion from self heating
and from damage that may occur during soldering. Metal
fi lm surface mount resistors are much less susceptible to
both problems. When high amplitude unwanted signals
are close in frequency to the desired signal frequency,
a multiple pole fi lter is required. High external source
resistance, combined with the 20pF of input capacitance,
will reduce the rated 10MHz bandwidth and increase
acquisition time beyond 500ns.
APPLICATIONS INFORMATION
51Ω
Figure 14. RC Input Filter
220pF
2.2μF
1
2
3
V
GND
A
DD
IN
LTC2362
CONV
SDO
SCK
6
5
4
236012 F14
IN
to ground
Reference Input
On the TS8 package of the LTC2360/LTC2361/LTC2362,
the voltage on the V
of the ADC. The reference voltage can range from V
down to 1.4V.
Input Range
The analog input of the LTC2360/LTC2361/LTC2362 is
driven single-ended with respect to GND from a single
supply. The input may swing up to V
and to V
also ideally suited for single-ended input use with V
V
between the A
package or V
stay fi xed at all ones, and if this difference goes below 0V,
the output code will stay fi xed at all zeros.
Figure 15 shows the ideal input/output characteristics for
the LTC2360/LTC2361/LTC2362. The code transitions oc-
cur midway between successive integer LSB values (i.e.,
0.5LSB, 1.5LSB, 2.5LSB, …, FS – 1.5LSB). The output
code is straight binary with 1LSB = V
package and 1LSB = V
LTC2360/LTC2361/LTC2362
REF
= 2.5V for single supply applications. If the difference
111...111
111...110
000...001
000...000
REF
for the TS8 package. The 0V to 2.5V range is
REF
Figure 15. Transfer Characteristics
0
IN
1LSB
for the TS8 package, the output code will
input and GND exceeds V
REF
INPUT VOLTAGE (V)
REF
pin defi nes the full-scale range
/4096 for the TS8 package.
DD
FS – 1LSB
DD
for the S6 package
236012 F15
/4096 for the S6
DD
for the S6
17
DD
236012f
DD
or