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| 型号： | AD7711AARZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 7/28页 |
| 文件大小： | 0K |
| 描述： | IC ADC 24BIT RTD I SOURCE 24SOIC |
| 标准包装： | 1 |
| 位数： | 24 |
| 采样率（每秒）： | 1.03k |
| 数据接口： | 串行 |
| 转换器数目： | 1 |
| 功率耗散（最大）： | 52.5mW |
| 电压电源： | 模拟和数字，双 ± |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 24-SOIC（0.295"，7.50mm 宽） |
| 供应商设备封装： | 24-SOIC W |
| 包装： | 管件 |
| 输入数目和类型： | 2 个差分，单极；2 个差分，双极 |
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2
AD7711A
–15–
REV. D
Table V. Typical External Series Resistance That Will Not
Introduce 20-Bit Gain Error
External Capacitance (pF)
Gain
0
50
100
500
1000
5000
1
145 k
W 34.5 kW 20.4 kW 5.2 kW 2.8 kW 700 W
2
70.5 k
W 16.9 kW 10 kW
2.5 k
W 1.4 kW 350 W
4
31.8 k
W 8.0 kW 4.8 kW 1.2 kW 670 W 170 W
8–128
13.4 k
W 3.6 kW 2.2 kW 550 W 300 W 80 W
The numbers in Tables IV and V assume a full-scale change on
the analog input. In any case, the error introduced due to longer
charging times is a gain error that can be removed using the
system calibration capabilities of the AD7711A provided that
the resultant span is within the span limits of the system calibra-
tion techniques for the AD7711A.
ANALOG INPUT FUNCTIONS
Analog Input Ranges
Both analog inputs are differential, programmable gain input
channels that can handle either unipolar or bipolar input signals.
The common-mode range of these inputs is from VSS to AVDD
provided that the absolute value of the analog input voltage lies
between VSS – 30 mV and AVDD + 30 mV.
The dc input leakage current is 10 pA maximum at 25
∞C
(
±1 nA over temperature). This results in a dc offset voltage
developed across the source impedance. However, this dc offset
effect can be compensated for by a combination of the differen-
tial input capability of the part and its system calibration mode.
Burnout Current
The AIN1(+) input of the AD7711A contains a 4.5
mA current
source that can be turned on/off via the control register. This
current source can be used in checking that a transducer has not
burned out or gone open circuit before attempting to take mea-
surements on that channel. If the current is turned on and al-
lowed to flow into the transducer and a measurement of the
input voltage on the AIN1 input is taken, it can indicate that
the transducer has burnout or gone open circuit. For normal
operation, this burnout current is turned off by writing a 0 to
the BO bit in the control register.
RTD Excitation Current
The AD7711A also contains a 400
mA constab current source
that is provided at the RTD current pin of the device. This
current can be turned on/off via the control register. Writing a 1
to the I/O bit of the control register enables the excitation current.
The temperature coefficient of the RTD current is typical
20 ppm/
∞C. For applications where this coefficient is too large,
the following scheme can be used to remove the drift error. The
conversion result from the AD7711A is ratiometric to the VREF
voltage. Therefore, if the VREF voltage varies with the RTD
temperature coefficient, the temperature drift of the current
source will be removed. Therefore, the reference voltage for the
part should be generated by placing a low TC resistor (6.25 k
W
for 2.5 V reference) in series with the constant current. The
RTD current source can be driven to within 2 V of AVDD. The
reference input of the AD7711A is differential so the REF
IN(+) and REF IN(–) of the AD7711A are driven from either
side of the resistor.
Antialias Considerations
The digital filter does not provide any rejection at integer mul-
tiples of the modulator sample frequency (n
19.5 kHz, where
n = 1, 2, 3 . . . ). This means that there are frequency bands,
±f3 dB wide (f3 dB is cutoff frequency selected by FS0 to FS11)
where noise passes unattenuated to the output. However, due to
the AD7711A’s high oversampling ratio, these bands occupy
only a small fraction of the spectrum, and most broadband noise
is filtered. In any case, because of the high oversampling ratio, a
simple, RC, single-pole filter is generally sufficient to attenuate
the signals in these bands on the analog input and thus provide
adequate antialiasing filtering.
If passive components are placed in front of the AD7711A, care
must be taken to ensure that the source impedance is low enough
so as not to introduce gain errors in the system. The dc input
impedance for the AD7711A is over 1 G
W. The input appears
as a dynamic load that varies with the clock frequency and with
the selected gain (see Figure 7). The input sample rate, as shown
in Table III, determines the time allowed for the analog input
capacitor, CIN, to be charged. External impedances result in a
longer charge time for this capacitor, which may result in gain
errors being introduced on the analog inputs. Table IV shows the
allowable external resistance/capacitance values such that no
gain error to the 16-bit level is introduced, while Table V shows
the allowable external resistance/capacitance values such that no
gain error to the 20-bit level is introduced. Both inputs of the
differential input channels look into similar input circuitry.
HIGH
IMPEDANCE
1G
CINT
11.5pF TYP
VBIAS
RINT
7k
TYP
AIN
SWITCHING FREQUENCY DEPENDS
ON
fCLKIN AND SELECTED GAIN
AD7711A
Figure 7. Analog Input Impedance
Table IV. Typical External Series Resistance That Will Not
Introduce 16-Bit Gain Error
External Capacitance (pF)
Gain
0
50
100
500
1000
5000
1
184 k
W 45.3 kW 27.1 kW 7.3 kW 4.1 kW 1.1 kW
2
88.6 k
W 22.1 kW 13.2 kW 3.6 kW 2.0 kW 560 W
4
41.4 k
W 10.6 kW 6.3 kW 1.7 kW 970 W 270 W
8–128
17.6 k
W 4.8 kW 2.9 kW 790 W 440 W 120
W
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| AD7711AN | 功能描述:IC ADC 24BIT RTD I SOURCE 24-DIP RoHS:否 类别:集成电路 (IC) >> 数据采集 - 模数转换器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- 位数:12 采样率（每秒）:3M 数据接口:- 转换器数目:- 功率耗散（最大）:- 电压电源:- 工作温度:- 安装类型:表面贴装 封装/外壳:SOT-23-6 供应商设备封装:SOT-23-6 包装:带卷 (TR) 输入数目和类型:- |
| AD7711ANZ | 功能描述:IC ADC 24BIT RTD I SOURCE 24-DIP RoHS:是 类别:集成电路 (IC) >> 数据采集 - 模数转换器 系列:- 其它有关文件:TSA1204 View All Specifications 标准包装:1 系列:- 位数:12 采样率（每秒）:20M 数据接口:并联 转换器数目:2 功率耗散（最大）:155mW 电压电源:模拟和数字 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:48-TQFP 供应商设备封装:48-TQFP（7x7） 包装:Digi-Reel® 输入数目和类型:4 个单端，单极；2 个差分，单极 产品目录页面:1156 (CN2011-ZH PDF) 其它名称:497-5435-6 |
| AD7711ANZ | 制造商:Analog Devices 功能描述:IC ADC 24-BIT SIGMA DELTA |
| AD7711AQ | 功能描述:IC ADC 24BIT RTD I SOURCE 24CDIP RoHS:否 类别:集成电路 (IC) >> 数据采集 - 模数转换器 系列:- 标准包装:1 系列:- 位数:14 采样率（每秒）:83k 数据接口:串行，并联 转换器数目:1 功率耗散（最大）:95mW 电压电源:双 ± 工作温度:0°C ~ 70°C 安装类型:通孔 封装/外壳:28-DIP（0.600"，15.24mm） 供应商设备封装:28-PDIP 包装:管件 输入数目和类型:1 个单端，双极 |
| AD7711AR | 功能描述:IC ADC 24BIT RTD I SOURCE 24SOIC RoHS:否 类别:集成电路 (IC) >> 数据采集 - 模数转换器 系列:- 标准包装:1 系列:- 位数:14 采样率（每秒）:83k 数据接口:串行，并联 转换器数目:1 功率耗散（最大）:95mW 电压电源:双 ± 工作温度:0°C ~ 70°C 安装类型:通孔 封装/外壳:28-DIP（0.600"，15.24mm） 供应商设备封装:28-PDIP 包装:管件 输入数目和类型:1 个单端，双极 |
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