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參數(shù)資料
| 型號(hào)： | ADS1251 |
| 廠商： | Texas Instruments, Inc. |
| 英文描述： | "ResolutionPlus 24-Bit |
| 中文描述： | ResolutionPlus 24 位 20kHz 低功耗模數(shù)轉(zhuǎn)換器 |
| 文件頁數(shù)： | 16/17頁 |
| 文件大?。?/td> | 323K |
| 代理商： | ADS1251 |
ADS1251
8
SBAS184A
www.ti.com
DELTA-SIGMA MODULATOR
The ADS1251 operates from a nominal system clock fre-
quency of 8MHz. The modulator frequency is fixed in relation
to the system clock frequency. The system clock frequency
is divided by 6 to derive the modulator frequency (fMOD).
Therefore, with a system clock frequency of 8MHz, the
modulator frequency is 1.333MHz. Furthermore, the
oversampling ratio of the modulator is fixed in relation to the
modulator frequency. The oversampling ratio of the modula-
tor is 64, and with the modulator frequency running at
1.333MHz, the data rate is 20.8kHz. Using a slower system
clock frequency will result in a lower data output rate, as
shown in Table I.
REFERENCE INPUT
The reference input takes an average current of 32
A with a
8MHz system clock. This current will be proportional to the
system clock. A buffered reference is recommended for the
ADS1251. The recommended reference circuit is shown in
Figure 2.
Reference voltages higher than 4.096V will increase the full-
scale range, while the absolute internal circuit noise of the
converter remains the same. This will decrease the noise in
terms of ppm of full-scale, which increases the effective
resolution (see typical characteristic “RMS Noise vs VREF
Voltage”).
DIGITAL FILTER
The digital filter of the ADS1251, referred to as a Sinc5 filter,
computes the digital result based on the most recent outputs
from the delta-sigma modulator. At the most basic level, the
digital filter can be thought of as averaging the modulator
results in a weighted form and presenting this average as the
digital output. The digital output rate, or data rate, scales
directly with the system clock frequency. This allows the data
output rate to be changed over a very wide range (five orders
of magnitude) by changing the system clock frequency.
However, it is important to note that the –3dB point of the
filter is 0.2035 times the data output rate, so the data output
rate should allow for sufficient margin to prevent attenuation
of the signal of interest.
As the conversion result is essentially an average, the
data-output rate determines the location of the resulting
notches in the digital filter (see Figure 3). Note that the first
notch is located at the data output rate frequency, and
subsequent notches are located at integer multiples of the
data output rate; this allows for rejection of not only the
fundamental frequency, but also harmonic frequencies. In
this manner, the data output rate can be used to set specific
notch frequencies in the digital filter response.
For example, if the rejection of power-line frequencies is
desired, then the data output rate can simply be set to the
power-line frequency. For 50Hz rejection, the system clock
TABLE I. CLK Rate versus Data Output Rate.
CLK (MHz)
DATA OUTPUT RATE (Hz)
8(1)
20,833
7.372800(1)
19,200
6.144000(1)
16,000
6.000000(1)
15,625
4.915200(1)
12,800
3.686400(1)
9600
3.072000(1)
8000
2.457600(1)
6400
1.843200(1)
4800
0.921600
2400
0.460800
1200
0.384000
1000
0.192000
500
0.038400
100
0.023040
60
0.019200
50
0.011520
30
0.009600
25
0.007680
20
0.006400
16.67
0.005760
15
0.004800
12.50
0.003840
10
NOTE: (1) Standard Clock Oscillator.
FIGURE 2. Recommended External Voltage Reference Circuit for Best Low-Noise Operation with the ADS1251.
0.10
F
+5V
10k
10
F
4
3
2
7
6
+
0.10
F
0.1
F
10
F
+
0.1
F
OPA350
0.1
F
+5V
3
1
2
To V
REF
Pin 8 of
the ADS1251
REF3040
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ADS1251EVM | 功能描述:數(shù)據(jù)轉(zhuǎn)換 IC 開發(fā)工具 ADS1251 ADC Eval Mod RoHS:否 制造商:Texas Instruments 產(chǎn)品:Demonstration Kits 類型:ADC 工具用于評(píng)估:ADS130E08 接口類型:SPI 工作電源電壓:- 6 V to + 6 V |
| ADS1251U | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC ResolutionPlus 24Bit 20kHz Lo-Power RoHS:否 制造商:Texas Instruments 通道數(shù)量:2 結(jié)構(gòu):Sigma-Delta 轉(zhuǎn)換速率:125 SPs to 8 KSPs 分辨率:24 bit 輸入類型:Differential 信噪比:107 dB 接口類型:SPI 工作電源電壓:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-32 |
| ADS1251U | 制造商:Texas Instruments 功能描述:IC 24BIT ADC SMD 1251 SOIC8 |
| ADS1251U | 制造商:Texas Instruments 功能描述:IC ADC 24BIT 20KSPS SOIC-8 |
| ADS1251U/2K5 | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC ResolutionPlus 24Bit 20kHz Lo-Power RoHS:否 制造商:Texas Instruments 通道數(shù)量:2 結(jié)構(gòu):Sigma-Delta 轉(zhuǎn)換速率:125 SPs to 8 KSPs 分辨率:24 bit 輸入類型:Differential 信噪比:107 dB 接口類型:SPI 工作電源電壓:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-32 |
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