LTC2351HUH-12#PBF Linear Technology, LTC2351HUH-12#PBF Datasheet - Page 15

• Manufacturer Part Number: LTC2351HUH-12#PBF
• Description: IC ADC 12BIT 1.5MSPS 32-QFN
• Manufacturer: Linear Technology

Specifications of LTC2351HUH-12#PBF

• Number Of Bits: 12
• 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

APPLICATIONS INFORMATION
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 de-
sired 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.
INPUT RANGE
The analog inputs of the LTC2351-12 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
negative full-scale.
+
and CH
CC
, provided the differential swing is no greater
ANALOG
ANALOG
–
INPUT
INPUT
at any input pair exceeds 2.5V (unipolar) or
*TIGHT TOLERANCE REQUIRED TO AVOID
Figure 1. RC Input Filter
APERTURE SKEW DEGRADATION
51Ω*
51Ω*
CC
10μF
. If the difference between the
47pF*
47pF*
11
1
2
3
4
5
CH0
CH0
V
GND
CH1
CH1
REF
LTC2351-12
+
–
+
–
235112 F01
INTERNAL REFERENCE
The LTC2351-12 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.
INPUT SPAN VERSUS REFERENCE VOLTAGE
The differential input range has a unipolar voltage span
that equals the difference between the voltage at the
reference buffer output V
ground. The differential input range of the ADC is 0V to
2.5V when using the internal reference. The internal ADC
is referenced to these two nodes. This relationship also
holds true with an external reference.
DIFFERENTIAL INPUTS
The ADC will always convert the difference of CH
CH
of inputs. The common mode rejection holds up at high
frequencies (see Figure 3.) The only requirement is that
both inputs not go below ground or exceed V
–
Figure 2. Overdriving V
, independent of the common mode voltage at any pair
3.5V TO 18V
REF
, (Pin 23) must be bypassed with a capacitor
LT1790-3
DD
. An external reference at 2.55V will
REF
REF
Pin with an External Reference
(Pin 23) and the voltage at
10μF
REF
LTC2351-12
23
22
pin can be overdriven
V
GND
REF
LTC2351-12
235112 F02
DD
.
+
15
minus
235112fa