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參數(shù)資料
| 型號(hào)： | ADS1256 |
| 英文描述： | Very Low Noise, 24-Bit Analog-to-Digital Converter |
| 中文描述： | 極低噪聲，24位模擬數(shù)字轉(zhuǎn)換器 |
| 文件頁(yè)數(shù)： | 15/39頁(yè) |
| 文件大小： | 427K |
| 代理商： | ADS1256 |
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SBAS288D JUNE 2003 REVISED AUGUST 2004
www.ti.com
15
OPEN/SHORT SENSOR DETECTION
The sensor detect current sources (SDCS) provide a
means to verify the integrity of the external sensor
connected to the ADS1255/6. When enabled, the SDCS
supply a current (I
SDC
) of approximately 0.5
μ
A, 2
μ
A, or
10
μ
A to the sensor through the input multiplexer. The
SDCS bits in the ADCON register enable the SDCS and
set the value of I
SDC
.
When the SDCS are enabled, the ADS1255/6
automatically turns on the analog input buffer regardless
of the BUFEN bit setting. This is done to prevent the input
circuitry from loading the SDCS. AIN
P
must stay below 3V
to be within the absolute input range of the buffer. To
ensure this condition is met, a 3V clamp will start sinking
current from AIN
P
to AGND if AIN
P
exceeds 3V. Note that
this clamp is activated only when the SDCS are enabled.
Figure 7 shows a simplified diagram of ADS1255/6 input
structure with the external sensor modeled as resistance
R
SENS
between two input pins. When the SDCS are
enabled, they source I
SDC
to the input pin connected to
AIN
P
and sink I
SDC
from the input pin connected to AIN
N
.
The two 25
series resistors, R
MUX,
model the
ADS1255/6 internal resistances. The signal measured
with the SDCS enabled equals the total IR drop:
I
SDC
×
(2R
MUX
+ R
SENS
). Note that when the sensor is a
direct short (that is, R
SENS
= 0), there will still be a small
signal measured by the ADS1255/6 when the SDCS are
enabled: I
SDC
×
2R
MUX
.
NOTE: Arrows indicate switch positions when the SDCS are enabled.
AVDD
Input
Buffer
3V
Clamp
Sensor Detect
Current Source
Sensor Detect
Current Source
R
MUX
25
AIN
N
AIN
P
R
MUX
25
R
SENS
Figure 7. Sensor Detect Circuitry
ANALOG INPUT BUFFER
To dramatically increase the input impedance presented
by the ADS1255/6, the low-drift chopper-stabilized buffer
can be enabled via the BUFEN bit in the STATUS register.
The input impedance with the buffer enabled can be
modeled by a resistor, as shown in Figure 8. Table 7 lists
the values of Z
EFF
for the different data rate settings. The
input impedance scales inversely with the frequency of
CLKIN. For example, if f
CLKIN
is reduced by half to
3.84MHz, Z
EFF
for a data rate of 50SPS will double from
80M
to 160M
.
AINP
AINN
Input
Multiplexer
AIN0
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
AIN7
AINCOM
A
ZEFF
Figure 8. Effective Impedance with Buffer On
Table 7. Input Impedance with Buffer On
DATA RATE
(SPS)
ZEFF
(M
)
30,000
10
15,000
10
7,500
10
3,750
10
2,000
10
1,000
20
500
40
100
40
60
40
≤
50
80
NOTE: fCLKIN = 7.68MHz.
With the buffer enabled, the voltage on the analog inputs
with respect to ground (listed in the Electrical
Characteristics as
Absolute Input Voltage
) must remain
between AGND and AVDD 2.0V. Exceeding this range
reduces performance, in particular the linearity of the
ADS1255/6. This same voltage range, AGND to
AVDD 2.0V, applies to the reference inputs when
performing a self gain calibration with the buffer enabled.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ADS1256EVM | 功能描述:數(shù)據(jù)轉(zhuǎn)換 IC 開(kāi)發(fā)工具 ADS1256 Eval Mod RoHS:否 制造商:Texas Instruments 產(chǎn)品:Demonstration Kits 類(lèi)型:ADC 工具用于評(píng)估:ADS130E08 接口類(lèi)型:SPI 工作電源電壓:- 6 V to + 6 V |
| ADS1256EVM-PDK | 功能描述:數(shù)據(jù)轉(zhuǎn)換 IC 開(kāi)發(fā)工具 ADS1256 Perf Demo Kit RoHS:否 制造商:Texas Instruments 產(chǎn)品:Demonstration Kits 類(lèi)型:ADC 工具用于評(píng)估:ADS130E08 接口類(lèi)型:SPI 工作電源電壓:- 6 V to + 6 V |
| ADS1256IDB | 制造商:BB 制造商全稱:BB 功能描述:Very Low Noise, 24-Bit Analog-to-Digital Converter |
| ADS1256IDBR | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 24Bit 30kSPS Very Lo-Noise Delta-Sigma 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(lèi)型:Differential 信噪比:107 dB 接口類(lèi)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 |
| ADS1256IDBRG4 | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 24Bit 30kSPS Very Lo-Noise Delta-Sigma 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(lèi)型:Differential 信噪比:107 dB 接口類(lèi)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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