参数资料
型号: LTC2381CMS-16#TRPBF
厂商: Linear Technology
文件页数: 2/24页
文件大小: 0K
描述: IC ADC 16BIT 1CH 250KSPS 16-MSOP
标准包装: 2,500
位数: 16
采样率(每秒): 250k
数据接口: 串行,SPI?
转换器数目: 1
功率耗散(最大): 4.25mW
电压电源: 模拟和数字
工作温度: 0°C ~ 70°C
安装类型: 表面贴装
封装/外壳: 16-TFSOP(0.118",3.00mm 宽)
供应商设备封装: 16-MSOP
包装: 带卷 (TR)
输入数目和类型: 1 个差分,双极
配用: DC1571A-C-ND - BOARD SAR ADC LTC2381-16
LTC2381-16
10
238116f
Figure 2. LTC2381-16 Transfer Function
INPUT VOLTAGE (V)
0V
OUTPUT
CODE
(TWO’S
COMPLEMENT)
–1
LSB
238116 F02
011...111
011...110
000...001
000...000
100...000
100...001
111...110
1
LSB
BIPOLAR
ZERO
111...111
FSR/2 – 1LSB
–FSR/2
FSR = +FS – –FS
1LSB = FSR/65536
RON
CIN
RON
REF
CIN
IN+
IN
BIAS
VOLTAGE
238116 F03
Figure 3. The Equivalent Circuit for the
Differential Analog Input of the LTC2381-16
circuit shown in Figure 3. The diodes at the input provide
ESD protection. In the acquisition phase, each input sees
approximately 45pF (CIN)fromthesamplingCDACinseries
with 40Ω (RON) from the on-resistance of the sampling
switch. Any unwanted signal that is common to both inputs
will be reduced by the common mode rejection of the
ADC. The inputs draw a current spike while charging the
CIN capacitors during acquisition. When the LTC2381-16
is not acquiring the input, the analog inputs draw only a
small leakage current.
INPUT DRIVE CIRCUITS
A low impedance source can directly drive the high
impedance inputs of the LTC2381-16 without gain error.
A high impedance source should be buffered to minimize
settling time during acquisition and to optimize the
distortion performance of the ADC. Minimizing settling
time is important even for DC inputs, because the ADC
inputs draw a current spike when entering acquisition.
For best performance, a buffer amplifier should be used to
drive the analog inputs of the LTC2381-16. The amplifier
provides low output impedance which produces fast
settling of the analog signal during the acquisition phase.
It also provides isolation between the signal source and
the current spike the ADC inputs draw.
Input Filtering
The noise and distortion of the buffer amplifier and signal
source must be considered since they add to the ADC noise
and distortion. Noisy input signals should be filtered prior
to the buffer amplifier input with an appropriate filter to
minimize noise. The simple 1-pole RC lowpass filter (LPF1)
shown in Figure 4 is sufficient for many applications.
Another filter network consisting of LPF2 and the 100Ω
series input resistors should be used between the buffer
and ADC inputs to both minimize the noise contribution
of the buffer and to help minimize disturbances reflected
into the buffer from sampling transients. Long RC time
constants at the analog inputs will slow down the settling
of the analog inputs. Therefore, LPF2 requires a wider
bandwidth than LPF1. A buffer amplifier with a low noise
density must be selected to minimize degradation of the
SNR. With the 482kHz lowpass filter shown in Figure 4,
the LT6350 provides the full data sheet performance of
the LTC2381-16.
High quality capacitors and resistors should be used in the
RC filters since these components can add distortion. NPO
and silver mica 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 film surface mount resistors
are much less susceptible to both problems.
APPLICATIONS INFORMATION
50Ω
3300pF
6600pF
50Ω
500Ω
100Ω
LPF2
LPF1
BW = 482kHz
BW = 48kHz
SINGLE-ENDED-
TO-DIFFERENTIAL
DRIVER
SINGLE-ENDED-
INPUT SIGNAL
LTC2381-16
IN+
IN
238116 F04
LT6350
Figure 4. Input Signal Chain
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