LTC2351HUH-14#TRPBF Linear Technology, LTC2351HUH-14#TRPBF Datasheet - Page 14

• Manufacturer Part Number: LTC2351HUH-14#TRPBF
• Description: IC ADC 14BIT 1.5MSPS 32-QFN
• Manufacturer: Linear Technology

Specifications of LTC2351HUH-14#TRPBF

• Number Of Bits: 14
• Sampling Rate (per Second): 1.5M
• Data Interface: Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 16.5mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 32-WFQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LTC2351-14
APPLICATIONS INFORMATION
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 LTC2351-14 noise and distortion. The small-signal
bandwidth of the sample-and-hold circuit is 50MHz. Any
noise or distortion products that are present at the analog
inputs will be summed over this entire bandwidth. Noisy
input circuitry should be fi ltered prior to the analog inputs.
A simple 1-pole RC fi lter is suffi cient for many applications.
For example, Figure 1 shows a 47pF capacitor from CH0
to ground and a 51Ω source resistor to limit the net input
bandwidth to 30MHz. The 47pF 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 13pF
of input capacitance, will reduce the rated 50MHz input
bandwidth and increase acquisition time beyond 39ns.
14
ANALOG
ANALOG
INPUT
INPUT
*TIGHT TOLERANCE REQUIRED TO AVOID
APERTURE SKEW DEGRADATION
Figure 1. RC Input Filter
51Ω*
51Ω*
10μF
47pF*
47pF*
11
1
2
3
4
5
CH0
CH0
V
GND
CH1
CH1
REF
LTC2351-14
+
–
+
–
235114 F01
+
INPUT RANGE
The analog inputs of the LTC2351-14 may be driven fully
differentially with a single supply. Either input may swing
up to V
than 2.5V with BIP (Pin 29) LOW, or ±1.25V with (BIP Pin
29) HIGH. The 0V to 2.5V range is also ideally suited for
single-ended input use with single supply applications. The
common mode range of the inputs extend from ground
to the supply voltage V
CH
1.25V (bipolar), the output code will stay fi xed at positive
full-scale, and if this difference goes below 0V (unipolar) or
–1.25V (bipolar), the output code will stay fi xed at nega-
tive full-scale.
INTERNAL REFERENCE
The LTC2351-14 has an on-chip, temperature compen-
sated, bandgap reference that is factory trimmed to 2.5V
to obtain a precise 2.5V input span. The reference amplifi er
output V
to ground. The reference amplifi er is stable with capaci-
tors of 1μF , or greater. For the best noise performance, a
10μF ceramic or a 10μF tantalum in parallel with a 0.1μF
ceramic is recommended. The V
with an external reference as shown in Figure 2. The
voltage of the external reference must be higher than the
2.5V of the open-drain P-channel output of the internal
reference. The recommended range for an external refer-
ence is 2.55V to V
see a DC quiescent load of 0.75mA and as much as 3mA
during conversion.
+
and CH
CC
3.5V to 18V
REF
, provided the differential swing is no greater
–
, (Pin 23) must be bypassed with a capacitor
at any input pair exceeds 2.5V (unipolar) or
Figure 2. External Reference
LT1790-3
DD
. An external reference at 2.55V will
CC
. If the difference between the
10μF
REF
23
22
pin can be overdriven
V
GND
REF
LTC2351-14
235114 F02
235114fb