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參數資料
| 型號： | AD7921AUJ-REEL7 |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | ADC |
| 英文描述： | 2-Channel, 2.35 V to 5.25 V 250 kSPS, 10-/12-Bit ADCs |
| 中文描述： | 2-CH 12-BIT SUCCESSIVE APPROXIMATION ADC, SERIAL ACCESS, PDSO8 |
| 封裝： | MO-193BA, TSOT-23 |
| 文件頁數： | 16/28頁 |
| 文件大小： | 312K |
| 代理商： | AD7921AUJ-REEL7 |
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AD7911/AD7921
TYPICAL CONNECTION DIAGRAM
Figure 22 shows a typical connection diagram for the AD7911/
AD7921. V
REF
is taken internally from V
DD
and as such V
DD
should be well decoupled. This provides an analog input range
of 0 V to V
DD
. The conversion result is output in a 16-bit word
with two leading zeros, followed by the channel identifier bit
that identifies the channel converted, followed by an invalid bit
that matches up to the channel converted, followed by the MSB
of the 12-bit or 10-bit result. For the AD7911, the 10-bit result is
followed by two trailing zeros. See the Serial Interface section.
Rev. 0 | Page 16 of 28
Alternatively, because the supply current required by the
AD7911/AD7921 is so low, a precision reference can be used as
the supply source to the AD7911/AD7921. A REF19x voltage
reference (REF195 for 5 V or REF193 for 3 V) can be used to
supply the required voltage to the ADC (see Figure 22). This
configuration is especially useful, if the power supply is quite
noisy or if the system supply voltages are at some value other
than 5 V or 3 V (for example, 15 V). The REF19x outputs a
steady voltage to the AD7911/AD7921. If the low dropout
REF193 is used, the current it needs to supply to the AD7911/
AD7921 is typically 1.5 mA. When the ADC is converting at a
rate of 250 kSPS, the REF193 needs to supply a maximum of
2 mA to the AD7911/AD7921. The load regulation of the
REF193 is typically 10 ppm/mA (REF193, V
S
= 5 V), which
results in an error of 20 ppm (60 μV) for the 2 mA drawn from
it. This corresponds to a 0.082 LSB error for the AD7921 with
V
DD
= 3 V from the REF193 and a 0.061 LSB error for the
AD7911.
For applications where power consumption is a concern, the
power-down mode of the ADC and the sleep mode of the
REF19x reference should be used to improve power perform-
ance. See the Modes of Operation section.
0
AD7911/
AD7921
V
DD
V
IN0
SERIAL
INTERFACE
0V TO V
DD
INPUT
μ
C/
μ
P
V
IN1
GND
SCLK
CS
DIN
DOUT
0.1
μ
F
10
μ
F
1
μ
F
TANT
0.1
μ
F
680nF
3V
5V
SUPPLY
1.5mA
REF193
Figure 22. REF193 as Power Supply to AD7911/AD7921
Table 6 provides some typical performance data with various
references used as a V
DD
source and a 50 kHz input tone under
the same setup conditions.
Table 6. AD7921 Performance for Various Voltage
References IC
Reference Tied to V
DD
AD7921 SNR Performance (dB)
AD780 at 3 V
73
REF193
72.42
ADR433
72.9
AD780 at 2.5 V
72.86
REF192
72.27
ADR421
72.75
ANALOG INPUT
Figure 23 shows an equivalent circuit of the analog input
structure of the AD7911/AD7921. The two diodes, D1 and D2,
provide ESD protection for the analog input. Care must be
taken to ensure that the analog input signal never exceeds the
supply rails by more than 300 mV, because this would cause
these diodes to become forward biased and start conducting
current into the substrate. The maximum current these diodes
can conduct without causing irreversible damage to the part is
10 mA.
0
C1
6pF
C2
20pF
R1
D1
D2
CONVERSION PHASE—SWITCH OPEN
TRACK PHASE—SWITCH CLOSED
V
DD
V
IN
Figure 23. Equivalent Analog Input Circuit
The capacitor C1 in Figure 23 is typically about 6 pF and can
primarily be attributed to pin capacitance. The resistor R1 is a
lumped component made up of the on resistance of a track-
and-hold switch and also includes the on resistance of the input
multiplexer. This resistor is typically about 100 . The capacitor
C2 is the ADC sampling capacitor and has a capacitance of
20 pF typically.
For ac applications, removing high frequency components from
the analog input signal is recommended using a band-pass filter
on the relevant analog input pin. In applications where
harmonic distortion and signal-to-noise ratio are critical, the
analog input should be driven from a low impedance source.
Large source impedances can significantly affect the ac
performance of the ADC. This might necessitate the use of an
input buffer amplifier. The choice of the op amp is a function of
the particular application.
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| AD7922AUJ-REEL7 | Circular Connector; No. of Contacts:7; Series:; Body Material:Aluminum Alloy; Connecting Termination:Solder; Connector Shell Size:16S; Circular Contact Gender:Socket; Circular Shell Style:Wall Mount Receptacle |
| AD7912AUJ-REEL7 | Circular Connector; No. of Contacts:5; Series:; Body Material:Aluminum Alloy; Connecting Termination:Solder; Connector Shell Size:16S; Circular Contact Gender:Pin; Circular Shell Style:Wall Mount Receptacle; Insert Arrangement:16S-8 RoHS Compliant: No |
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| AD7921AUJZ-R2 | 功能描述:IC ADC 12BIT DUAL LP TSOT-23-8 RoHS:是 類別:集成電路 (IC) >> 數據采集 - 模數轉換器 系列:- 標準包裝:2,500 系列:- 位數:16 采樣率（每秒）:15 數據接口:MICROWIRE?，串行，SPI? 轉換器數目:1 功率耗散（最大）:480µW 電壓電源:單電源 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:38-WFQFN 裸露焊盤 供應商設備封裝:38-QFN（5x7） 包裝:帶卷 (TR) 輸入數目和類型:16 個單端，雙極；8 個差分，雙極 配用:DC1011A-C-ND - BOARD DELTA SIGMA ADC LTC2494 |
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