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參數資料
| 型號： | ADS1256 |
| 英文描述： | Very Low Noise, 24-Bit Analog-to-Digital Converter |
| 中文描述： | 極低噪聲，24位模擬數字轉換器 |
| 文件頁數： | 17/39頁 |
| 文件大?。?/td> | 427K |
| 代理商： | ADS1256 |
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SBAS288D JUNE 2003 REVISED AUGUST 2004
www.ti.com
17
The charging of the input capacitors draws a transient
current from the sensor driving the ADS1255/6 inputs. The
average value of this current can be used to calculate an
effective impedance Z
EFF
where Z
EFF
= V
IN
/ I
AVERAGE
.
Figure 11 shows the input circuitry with the capacitors and
switches of Figure 9 replaced by their effective
impedances. These impedances scale inversely with the
CLKIN frequency. For example, if f
CLKIN
is reduced by a
factor of two, the impedances will double. They also
change with the PGA setting. Table 10 lists the effective
impedances with the buffer off for f
CLKIN
= 7.68MHz.
Zeff
A
=
τ
SAMPLE
/C
A
Zeff
B
=
τ
SAMPLE
/C
B
Zeff
A
=
τ
SAMPLE
/C
A
AVDD/2
AVDD/2
Input
Multiplexer
AIN0
AIN1
AIN
P
AIN
N
AIN2
AIN3
AIN4
AIN5
AIN6
AIN7
AINCOM
A
O
Figure 11. Analog Input Effective Impedances
with Buffer Off
Table 10. Analog Input Impedances with Buffer Off
PGA
SETTING
ZeffA
(k
)
ZeffB
(k
)
1
260
220
2
130
110
4
65
55
8
33
28
16
16
14
32
8
7
64
8
7
NOTE: fCLKIN = 7.68MHz.
VOLTAGE REFERENCE INPUTS (VREFP, VREFN)
The voltage reference for the ADS1255/6 A/D converter is
the differential voltage between VREFP and VREFN:
V
REF
= VREFP VREFN. The reference inputs use a
structure similar to that of the analog inputs with the
circuitry on the reference inputs of Figure 12. The load
presented by the switched capacitor can be modeled with
an
effective
impedance
f
CLKIN
= 7.68MHz. The temperature coefficient of the
effective impedance of the voltage reference inputs is
approximately 35ppm/
°
C.
(Z
EFF
)
of
18.5k
for
AVDD
Self Gain
Calibration
AIN
P
(1) f
CLKIN
= 7.68MHz
AIN
N
Z
EFF
= 18.5k
(1)
VREFP
VREFN
AVDD
ESD
Protection
Figure 12. Simplified Reference Input Circuitry
ESD diodes protect the reference inputs. To keep these
diodes from turning on, make sure the voltages on the
reference pins do not go below AGND by more than
100mV, and likewise do not exceed AVDD by 100mV:
100mV < (VREFP or VREFN) < AVDD + 100mV
During self gain calibration, all the switches in the input
multiplexer are opened, VREFN is internally connected to
AIN
N
, and VREFP is connected to AIN
P
. The input buffer
may be disabled or enabled during calibration. When the
buffer is disabled, the reference pins will be driving the
circuitry shown in Figure 9 during self gain calibration,
resulting in increased loading. To prevent this additional
loading from introducing gain errors, make sure the
circuitry driving the reference pins has adequate drive
capability. When the buffer is enabled, the loading on the
reference pins will be much less, but the buffer will limit the
allowable voltage range on VREFP and VREFN during
self or self gain calibration as the reference pins must
remain within the specified input range of the buffer in
order to establish proper gain calibration.
A high-quality reference voltage is essential for achieving
the best performance from the ADS1255/6. Noise and drift
on the reference degrade overall system performance. It
is especially critical that special care be given to the
circuitry generating the reference voltages and their layout
when operating in the low-noise settings (that is, with low
data rates) to prevent the voltage reference from limiting
performance.
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PDF描述 |
|---|---|
| ADS1271 | 24 BIT WIDE BANDWIDTH ANALOG TO DIGITAL CONVERTER |
| ADS1271IPW | 24 BIT WIDE BANDWIDTH ANALOG TO DIGITAL CONVERTER |
| ADS1271IPWR | 24 BIT WIDE BANDWIDTH ANALOG TO DIGITAL CONVERTER |
| ADS1271EVM-PDK | modular EVM form factor |
| ADS1271EVM | modular EVM form factor |
相關代理商/技術參數 |
參數描述 |
|---|---|
| ADS1256EVM | 功能描述:數據轉換 IC 開發(fā)工具 ADS1256 Eval Mod RoHS:否 制造商:Texas Instruments 產品:Demonstration Kits 類型:ADC 工具用于評估:ADS130E08 接口類型:SPI 工作電源電壓:- 6 V to + 6 V |
| ADS1256EVM-PDK | 功能描述:數據轉換 IC 開發(fā)工具 ADS1256 Perf Demo Kit RoHS:否 制造商:Texas Instruments 產品:Demonstration Kits 類型:ADC 工具用于評估:ADS130E08 接口類型: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:模數轉換器 - ADC 24Bit 30kSPS Very Lo-Noise Delta-Sigma RoHS:否 制造商:Texas Instruments 通道數量:2 結構:Sigma-Delta 轉換速率:125 SPs to 8 KSPs 分辨率:24 bit 輸入類型:Differential 信噪比:107 dB 接口類型: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 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-32 |
| ADS1256IDBRG4 | 功能描述:模數轉換器 - ADC 24Bit 30kSPS Very Lo-Noise Delta-Sigma RoHS:否 制造商:Texas Instruments 通道數量:2 結構:Sigma-Delta 轉換速率:125 SPs to 8 KSPs 分辨率:24 bit 輸入類型:Differential 信噪比:107 dB 接口類型: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 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-32 |
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