参数资料
型号: LTC2351CUH-12#TR
厂商: LINEAR TECHNOLOGY CORP
元件分类: ADC
英文描述: 6-CH 12-BIT PROPRIETARY METHOD ADC, SERIAL ACCESS, PQCC32
封装: 5 X 5 MM, PLASTIC, MO-220WHHD, QFN-32
文件页数: 6/20页
文件大小: 273K
代理商: LTC2351CUH-12#TR
14
LTC2351-12
235112f
APPLICATIO S I FOR ATIO
WU
UU
INPUT FILTERING AND SOURCE IMPEDANCE
The noise and the distortion of the input amplifier and
other circuitry must be considered since they will add to
the LTC2351-12 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 filtered prior to the analog inputs.
A simple 1-pole RC filter is sufficient for many applica-
tions. For example, Figure 1 shows a 47pF capacitor from
CHO+ to ground and a 51
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 cir-
cuitry. High quality capacitors and resistors should be
used since these components can add distortion. NPO and
silvermica type dielectric capacitors have excellent linear-
ity. Carbon surface mount resistors can generate distor-
tion from self heating and from damage that may occur
during soldering. Metal film 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 filter is required.
High external source resistance, combined with 13pF of
input capacitance, will reduce the rated 50MHz input band-
width 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 VCC, provided the differential swing is no greater 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 VCC. If the difference between the CH+
and CHat any input pair exceeds 2.5V (unipolar) or 1.25V
(bipolar), the output code will stay fixed at positive full-
scale, and if this difference goes below 0V (unipolar) or
–1.25V (bipolar), the output code will stay fixed at negative
full-scale.
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 ampli-
fier output VREF, (Pin 23) must be bypassed with a capaci-
tor to ground. The reference amplifier is stable with capaci-
tors of 1
F or greater. For the best noise performance, a
10
F ceramic or a 10F tantalum in parallel with a 0.1F
ceramic is recommended. The VREF pin can be overdriven
with an external reference as shown in Figure 2. The volt-
age of the external reference must be higher than the 2.5V
of the open-drain P-channel output of the internal refer-
ence. The recommended range for an external reference
is 2.55V to VDD. An external reference at 2.55V will see a
DC quiescent load of 0.75mA and as much as 3mA
during conversion.
Figure 1. RC Input Filter
LTC2351-12
CH0+
CH0
VREF
GND
235112 F01
1
2
11
3
10
F
47pF*
51
*
CH1+
CH1
4
5
47pF*
*TIGHT TOLERANCE REQUIRED TO AVOID
APERTURE SKEW DEGRADATION
51
*
ANALOG
INPUT
ANALOG
INPUT
Figure 2. Overdriving VREF Pin with an External Reference
LTC2351-12
VREF
GND
235112 F02
23
22
10
F
LT1790-3
3.5V to 18V
相关PDF资料
PDF描述
LTC2351CUH-12 6-CH 12-BIT PROPRIETARY METHOD ADC, SERIAL ACCESS, PQCC32
LTC2351IUH-12#TR 6-CH 12-BIT PROPRIETARY METHOD ADC, SERIAL ACCESS, PQCC32
LTC2355CMSE-12#TR 1-CH 12-BIT PROPRIETARY METHOD ADC, SERIAL ACCESS, PDSO10
LTC2355IMSE-12#TR 1-CH 12-BIT PROPRIETARY METHOD ADC, SERIAL ACCESS, PDSO10
LTC2355IMSE-14#TR 1-CH 14-BIT PROPRIETARY METHOD ADC, SERIAL ACCESS, PDSO10
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