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参数资料
| 型号： | DDC112U/1K |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | ADC |
| 英文描述： | 2-CH 20-BIT DELTA-SIGMA ADC, SERIAL ACCESS, PDSO28 |
| 封装： | GREEN, PLASTIC, SOIC-28 |
| 文件页数： | 3/34页 |
| 文件大小： | 776K |
| 代理商： | DDC112U/1K |
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DDC112
11
SBAS085B
www.ti.com
Determining the Integration Capacitor (CF) Value
The value of the integrator’s feedback capacitor, the integra-
tion period, and the reference voltage determine the positive
full-scale (+FS) value of the DDC112. The approximate
positive full-scale value of the DDC112 is given by the
following equations:
QI
T
QV
C
I
VC
T
or
C
IT
V
IN
INT
FS
REF
F
FS
REF
F
INT
F
FS
INT
REF
=×
=
(
)
×
= (
)
×
=
×
096
.
(.
)
The
0.96 factor allows the front end integrators to reach full-
scale without having to completely swing to ground. The
negative full-scale (–FS) range is approximately 0.4% of the
positive full-scale range. For example, Range 5 has a nomi-
nal +FS range of 250pC. The –FS range is then approxi-
mately –1pC. This relationship holds for external capacitors
as well and is independent of VREF (for VREF within the
allowable range, see the Electrical Characteristics table).
Integration Capacitors
There are seven different capacitors available on-chip for
each side of each channel in the DDC112. These internal
capacitors are trimmed in production to achieve the specified
performance for range error of the DDC112. The range
control pins (RANGE0-RANGE2) change the capacitor value
for all four integrators. Consequently, both inputs and both
sides of each input will always have the same full-scale
range unless external capacitors are used.
External integration capacitors may be used instead of the
internal capacitors values by setting [RANGE2-RANGE0 =
000]. The external capacitor pin connections are summa-
rized in Table II. Usually, all four external capacitors are
equal in value; however, it is possible to have differing pairs
of external capacitors between Input 1 and Input 2 of the
DDC112. Regardless of the selected value of the capacitor,
it is strongly recommended that the capacitors for sides A
and B be the same.
INTEGRATOR
DDC112U, UK
DDC112Y, YK
Channel
Side
5 and 6
1 and 2
1
A
3 and 4
31 and 32
1
B
23 and 24
2
A
25 and 26
2
B
TABLE II. External Capacitor Connections with Range Con-
figuration of RANGE2-RANGE0 = 000.
Since the range accuracy depends on the characteristics of
the integration capacitor, they must be carefully selected. An
external integration capacitor should have low-voltage coef-
ficient, temperature coefficient, memory, and leakage cur-
rent. The optimum selection depends on the requirements of
the specific application. Suitable types include chip-on-glass
(COG) ceramic, polycarbonate, polystyrene, and silver mica.
Voltage Reference
The external voltage reference is used to reset the integra-
tion capacitors before an integration cycle begins. It is also
used by the
Σ converter while the converter is measuring
the voltage stored on the integrators after an integration
cycle ends. During this sampling, the external reference must
supply charge needed by the
Σ converter. For an integration
time of 500
s, this charge translates to an average V
REF
current of approximately 150
A. The amount of charge
needed by the
Σ converter is independent of the integration
time; therefore, increasing the integration time lowers the
average current. For example, an integration time of 1000
s
lowers to average VREF current to 75A.
It is critical that VREF be stable during the different modes of
operation in Figure 5. The
Σ converter measures the volt-
age on the integrator with respect to VREF. Since the
integrator’s capacitors are initially reset to VREF, any droop in
VREF from the time the capacitors are reset to the time when
the converter measures the integrator’s output will introduce
an offset. It is also important that VREF be stable over longer
periods of time as changes in VREF correspond directly to
changes in the full-scale range. Finally, VREF should intro-
duce as little additional noise as possible.
For reasons mentioned above, it is strongly recommended
that the external reference source be buffered with an
operational amplifier, as shown in Figure 6. In this circuit,
the voltage reference is generated by a 4.096V reference.
FIGURE 6. Recommended External Voltage Reference Circuit for Best Low-Noise Operation with the DDC112.
0.10
F
+5V
10k
10
F
4
3
2
1
2
7
6
+
0.10
F
0.1
F
10
F
+
OPA350
To V
REF
Pin 22 of
the DDC112
REF3040
+5V
0.47
F
EXTERNAL CAPACITOR PINS
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相关代理商/技术参数 |
参数描述 |
|---|---|
| DDC112UG4 | 功能描述:模数转换器 - ADC Dual Current Input 20-Bit RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32 |
| DDC112UK | 功能描述:模数转换器 - ADC Dual Current Input 20-Bit RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32 |
| DDC112UK | 制造商:Texas Instruments 功能描述:DUAL CURRENT INPUT 20 BIT ANALOG/DIGITAL |
| DDC112UK | 制造商:Texas Instruments 功能描述:20BIT ADC DUAL SMD SOIC28 112 |
| DDC112UK/1K | 功能描述:模数转换器 - ADC Dual Current Input 20-Bit RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32 |
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