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參數(shù)資料
| 型號(hào)： | AD7923 |
| 廠商： | Analog Devices, Inc. |
| 元件分類(lèi)： | ADC |
| 英文描述： | SHROUDED HEADER 60 PIN STRAIGHT |
| 中文描述： | 4通道，200 kSPS的，12位序列ADC的16引腳TSSOP |
| 文件頁(yè)數(shù)： | 12/20頁(yè) |
| 文件大?。?/td> | 430K |
| 代理商： | AD7923 |
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–12–
AD7923
REV. 0
When the ADC starts a conversion (see Figure 5), SW2 will
open and SW1 will move to position B, causing the comparator
to become unbalanced. The Control Logic and the capacitive
DAC are used to add and subtract fixed amounts of charge from
the sampling capacitor to bring the comparator back into a
balanced condition. When the comparator is rebalanced, the
conversion is complete. The Control Logic generates the ADC
output code. Figures 7 and 8 show the ADC transfer functions.
V
IN
0
.
.
V
IN
3
AGND
A
B
SW1
SW2
COMPARATOR
CONTROL
LOGIC
4k
CAPACITIVE
DAC
Figure 5. ADC Conversion Phase
Analog Input
Figure 6 shows an equivalent circuit of the analog input struc-
ture of the AD7923. The two diodes D1 and D2 provide ESD
protection for the analog inputs. Care must be taken to ensure
that the analog input signal never exceeds the supply rails by
more than 200 mV. This will cause these diodes to become
forward-biased and start conducting current into the substrate.
10 mA is the maximum current these diodes can conduct with-
out causing irreversible damage to the part. Capacitor C1 in
Figure 6 is typically about 4 pF and can primarily be attributed
to pin capacitance. The resistor R1 is a lumped component
made up of the on resistance of the track-and-hold switch and
also includes the on resistance of the input multiplexer. The
total resistance is typically about 400
W
. Capacitor C2 is the
ADC sampling capacitor and has a capacitance of 30 pF typi-
cally. For ac applications, removing high frequency components
from the analog input signal is recommended by using an RC
low-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 will significantly affect the ac perfor-
mance of the ADC. This may necessitate the use of an input
buffer amplifier. The choice of the op amp will be a function of
the particular application.
When no amplifier is used to drive the analog input, the source
impedance should be limited to low values. The maximum source
impedance will depend on the amount of total harmonic distortion
(THD) that can be tolerated. The THD will increase as the
source impedance increases and performance will degrade.
(See TPC 5.)
V
IN
C1
4pF
C2
30pF
R1
D1
D2
AV
DD
CONVERSION PHASE: SWITCH OPEN
TRACK PHASE: SWITCH CLOSED
Figure 6. Equivalent Analog Input Circuit
ADC TRANSFER FUNCTION
The output coding of the AD7923 is either straight binary or
twos complement, depending on the status of the LSB in the
Control Register. The designed code transitions occur at succes-
sive LSB values (i.e., 1 LSB, 2 LSBs, and so on). The LSB size
is REF
IN
/4096 for the AD7923. The ideal transfer characteristic
for the AD7923 when straight binary coding is selected is shown
in Figure 7, and the ideal transfer characteristic for the AD7923
when twos complement coding is selected is shown in Figure 8.
000…000
0V
ANALOG INPUT
111…111
111…110
111…000
011…111
000…001
000…010
1 LSB
+V
REF
1 LSB
1LSB V
REF
/4096
NOTE: V
REF
IS EITHER REF
IN
OR 2 REF
IN
A
Figure 7. Straight Binary Transfer Characteristic
–V
REF
1LSB
A
ANALOG INPUT
+V
REF
1LSB
1LSB 2 V
REF
4096
V
REF
1LSB
100…000
011…111
011…110
000…001
000…000
100…001
100…010
111…111
Figure 8. Twos Complement Transfer Characteristic with
REF
IN
±
REF
IN
Input Range
Handling Bipolar Input Signals
Figure 9 shows how useful the combination of the 2
￥
REF
IN
input range and the twos complement output coding scheme is
for handling bipolar input signals. If the bipolar input signal is
biased about REF
IN
and twos complement output coding is
selected, then REF
IN
becomes the zero code point, –REF
IN
is
negative full scale, and +REF
IN
becomes positive full scale, with
a dynamic range of 2
￥
REF
IN
.
TYPICAL CONNECTION DIAGRAM
Figure 10 shows a typical connection diagram for the AD7923. In
this setup the AGND pin is connected to the analog ground plane
of the system. In Figure 10, REF
IN
is connected to a decoupled
2.5 V supply from a reference source, the AD780, to provide an
analog input range of 0 V to 2.5 V (if RANGE bit is 1) or 0 V
to 5 V (if RANGE bit is 0). Although the AD7923 is connected
to a V
DD
of 5 V, the serial interface is connected to a 3 V micro-
processor. The V
DRIVE
pin of the AD7923 is connected to the same
3 V supply of the microprocessor to allow a 3 V logic interface
(see the Digital Inputs section). The conversion result is output in
a 16-bit word. This 16-bit data stream consists of two leading zeros,
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參數(shù)描述 |
|---|---|
| AD7923_11 | 制造商:AD 制造商全稱(chēng):Analog Devices 功能描述:4-Channel, 200 kSPS 12-Bit ADC with Sequencer in 16-Lead TSSOP |
| AD7923BRU | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 4CH 200 kSPS 12-Bit W/ Sequencer RoHS:否 制造商:Analog Devices 通道數(shù)量: 結(jié)構(gòu): 轉(zhuǎn)換速率: 分辨率: 輸入類(lèi)型: 信噪比: 接口類(lèi)型: 工作電源電壓: 最大工作溫度: 安裝風(fēng)格: 封裝 / 箱體: |
| AD7923BRU-REEL | 制造商:Analog Devices 功能描述:ADC Single SAR 200ksps 12-bit Serial 16-Pin TSSOP T/R 制造商:Analog Devices 功能描述:ADC SGL SAR 200KSPS 12-BIT SERL 16TSSOP - Tape and Reel |
| AD7923BRU-REEL7 | 制造商:Analog Devices 功能描述:ADC Single SAR 200ksps 12-bit Serial 16-Pin TSSOP T/R |
| AD7923BRUZ | 功能描述:IC ADC 12BIT 4CH W/SEQ 16TSSOP RoHS:是 類(lèi)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:microPOWER™ 位數(shù):8 采樣率（每秒）:1M 數(shù)據(jù)接口:串行，SPI? 轉(zhuǎn)換器數(shù)目:1 功率耗散（最大）:- 電壓電源:模擬和數(shù)字 工作溫度:-40°C ~ 125°C 安裝類(lèi)型:表面貼裝 封裝/外殼:24-VFQFN 裸露焊盤(pán) 供應(yīng)商設(shè)備封裝:24-VQFN 裸露焊盤(pán)（4x4） 包裝:Digi-Reel® 輸入數(shù)目和類(lèi)型:8 個(gè)單端，單極 產(chǎn)品目錄頁(yè)面:892 (CN2011-ZH PDF) 其它名稱(chēng):296-25851-6 |
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