- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄375238 > AD7711A (Analog Devices, Inc.) Signal Conditioning ADC with RTD Current Source(帶RTD電流源信號調(diào)節(jié)A/D轉(zhuǎn)換器) PDF資料下載
參數(shù)資料
| 型號： | AD7711A |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Signal Conditioning ADC with RTD Current Source(帶RTD電流源信號調(diào)節(jié)A/D轉(zhuǎn)換器) |
| 中文描述： | 信號調(diào)理ADC，具有電阻電流源（帶電阻電流源信號調(diào)節(jié)的A / D轉(zhuǎn)換器） |
| 文件頁數(shù)： | 15/27頁 |
| 文件大小： | 237K |
| 代理商： | AD7711A |
第1頁第2頁第3頁第4頁第5頁第6頁第7頁第8頁第9頁第10頁第11頁第12頁第13頁第14頁當(dāng)前第15頁第16頁第17頁第18頁第19頁第20頁第21頁第22頁第23頁第24頁第25頁第26頁第27頁
2
AD7711A
–15–
REV. C
Table V. Typical External Series Resistance That Will Not
Introduce 20-Bit Gain Error
External Capacitance (pF)
50
100
34.5 k
20.4 k
5.2 k
70.5 k
16.9 k
10 k
31.8 k
8.0 k
13.4 k
3.6 k
Gain
0
145 k
500
1000
2.8 k
1.4 k
670
300
5000
700
350
170
80
1
2
4
8–128
2.5 k
1.2 k
550
4.8 k
2.2 k
The numbers in the above tables assume a full-scale change on
the analog input. In any case, the error introduced due to longer
charging times is a gain error which 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 which can handle either unipolar or bipolar input
signals. The common-mode range of these inputs is from V
SS
to
AV
DD
provided that the absolute value of the analog input volt-
age lies between V
SS
–30 mV and AV
DD
+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
μ
A 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 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 opera-
tion, 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
μ
A constant current source,
which 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 IO 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 V
REF
voltage. Therefore, if the V
REF
voltage varies with the RTD
temperature coefficient, the temperature drift of the current
source will be removed. Hence, the reference voltage for the
part should be generated by placing a low t.c. resistor (6.25 k
for 2.5 V reference) in series with the constant current. The
RTD current source can be driven to within 2 V of AV
DD
. 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,
±
f
3 dB
wide (f
3 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
. The input appears
as a dynamic load which 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, C
IN
, to be charged. External impedances result
in a longer charge time for this capacitor and this 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
V
C
11.5pF TYP
V
BIAS
R
INT
7k
V
AIN
SWITCHING FREQUENCY DEPENDS
ON
f
CLKIN
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)
50
100
45.3 k
27.1 k
7.3 k
88.6 k
22.1 k
13.2 k
3.6 k
41.4 k
10.6 k
6.3 k
17.6 k
4.8 k
Gain
0
184 k
500
1000
4.1 k
2.0 k
970
440
5000
1.1 k
560
270
120
1
2
4
8–128
1.7 k
790
2.9 k
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| AD7711 | LC2MOS Signal Conditioning ADC with RTD Excitation Currents(RTD激勵電流LC2MOS信號調(diào)節(jié)A/D轉(zhuǎn)換器) |
| AD7714(中文) | Signal Conditioning ADC(信號調(diào)節(jié)A/D轉(zhuǎn)換器) |
| AD7715 | 3 V/5 V, 450 mA 16-Bit, Sigma-Delta ADC(16位∑△A/D轉(zhuǎn)換器) |
| AD7716BP | LC2MOS 22-Bit Data Acquisition System |
| AD7716BS | LC2MOS 22-Bit Data Acquisition System |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD7711AAN | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Analog-to-Digital Converter， 24-Bit |
| AD7711AAR | 功能描述:IC ADC 24BIT RTD I SOURCE 24SOIC RoHS:否 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 模數(shù)轉(zhuǎn)換器 系列:- 標(biāo)準(zhǔn)包裝:1 系列:- 位數(shù):14 采樣率（每秒）:83k 數(shù)據(jù)接口:串行，并聯(lián) 轉(zhuǎn)換器數(shù)目:1 功率耗散（最大）:95mW 電壓電源:雙 ± 工作溫度:0°C ~ 70°C 安裝類型:通孔 封裝/外殼:28-DIP（0.600"，15.24mm） 供應(yīng)商設(shè)備封裝:28-PDIP 包裝:管件 輸入數(shù)目和類型:1 個(gè)單端，雙極 |
| AD7711AARZ | 功能描述:IC ADC 24BIT RTD I SOURCE 24SOIC RoHS:是 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 模數(shù)轉(zhuǎn)換器 系列:- 其它有關(guān)文件:TSA1204 View All Specifications 標(biāo)準(zhǔn)包裝:1 系列:- 位數(shù):12 采樣率（每秒）:20M 數(shù)據(jù)接口:并聯(lián) 轉(zhuǎn)換器數(shù)目:2 功率耗散（最大）:155mW 電壓電源:模擬和數(shù)字 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:48-TQFP 供應(yīng)商設(shè)備封裝:48-TQFP（7x7） 包裝:Digi-Reel® 輸入數(shù)目和類型:4 個(gè)單端，單極；2 個(gè)差分，單極 產(chǎn)品目錄頁面:1156 (CN2011-ZH PDF) 其它名稱:497-5435-6 |
| AD7711AN | 功能描述:IC ADC 24BIT RTD I SOURCE 24-DIP RoHS:否 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 模數(shù)轉(zhuǎn)換器 系列:- 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:- 位數(shù):12 采樣率（每秒）:3M 數(shù)據(jù)接口:- 轉(zhuǎn)換器數(shù)目:- 功率耗散（最大）:- 電壓電源:- 工作溫度:- 安裝類型:表面貼裝 封裝/外殼:SOT-23-6 供應(yīng)商設(shè)備封裝:SOT-23-6 包裝:帶卷 (TR) 輸入數(shù)目和類型:- |
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。