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参数资料
| 型号： | EVAL-AD7791EBZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 10/20页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL FOR AD7791 |
| 标准包装： | 1 |
| ADC 的数量： | 1 |
| 位数： | 24 |
| 采样率（每秒）： | 120 |
| 数据接口： | SPI?、QSPI?、MICROWIRE? 和 DSP |
| 工作温度： | -40°C ~ 105°C |
| 已用 IC / 零件： | AD7791 |
| 已供物品： | 板 |
AD7791
Data Sheet
Rev. A | Page 18 of 20
CIRCUIT DESCRIPTION
ANALOG INPUT CHANNEL
The AD7791 has one differential analog input channel. This is
connected to the on-chip buffer amplifier when the device is
operated in buffered mode and directly to the modulator when
the device is operated in unbuffered mode. In buffered mode
(the BUF bit in the mode register is set to 1), the input channel
feeds into a high impedance input stage of the buffer amplifier.
Therefore, the input can tolerate significant source impedances
and is tailored for direct connection to external resistive-type
sensors such as strain gauges or resistance temperature detec-
tors (RTDs).
When BUF = 0, the part is operated in unbuffered mode. This
results in a higher analog input current. Note that this
unbuffered input path provides a dynamic load to the driving
source. Therefore, resistor/capacitor combinations on the input
pins can cause dc gain errors, depending on the output
impedance of the source that is driving the ADC input. Table 15
shows the allowable external resistance/capacitance values for
unbuffered mode such that no gain error at the 20-bit level is
introduced.
Table 15. External R-C Combination for No 20-Bit Gain Error
C (pF)
R ()
50
16.7K
100
9.6K
500
2.2K
1000
1.1K
5000
160
The absolute input voltage range in buffered mode is restricted
to a range between GND + 100 mV and VDD – 100 mV. Care
must be taken in setting up the common-mode voltage so that
these limits are not exceeded. Otherwise, there will be degrada-
tion in linearity and noise performance.
The absolute input voltage in unbuffered mode includes the
range between GND – 30 mV and VDD + 30 mV as a result of
being unbuffered. The negative absolute input voltage limit does
allow the possibility of monitoring small true bipolar signals
with respect to GND.
BIPOLAR/UNIPOLAR CONFIGURATION
The analog input to the AD7791 can accept either unipolar or
bipolar input voltage ranges. A bipolar input range does not
imply that the part can tolerate negative voltages with respect to
system GND. Unipolar and bipolar signals on the AIN(+) input
are referenced to the voltage on the AIN(–) input. For example,
if AIN(–) is 2.5 V and the ADC is configured for unipolar
mode, the input voltage range on the AIN(+) pin is 2.5 V to 5 V.
If the ADC is configured for bipolar mode, the analog input
range on the AIN(+) input is 0 V to 5 V. The bipolar/unipolar
option is chosen by programming the B/U bit in the mode
register.
DATA OUTPUT CODING
When the ADC is configured for unipolar operation, the output
code is natural (straight) binary with a zero differential input
voltage resulting in a code of 00...00, a midscale voltage
resulting in a code of 100...000, and a full-scale input voltage
resulting in a code of 111...111. The output code for any analog
input voltage can be represented as
Code = 2N × (AIN/VREF)
When the ADC is configured for bipolar operation, the output
code is offset binary with a negative full-scale voltage resulting
in a code of 000...000, a zero differential input voltage resulting
in a code of 100...000, and a positive full-scale input voltage
resulting in a code of 111...111. The output code for any analog
input voltage can be represented as
Code = 2N–1 × [(AIN/VREF) + 1]
where AIN is the analog input voltage and N = 24.
REFERENCE INPUT
The AD7791 has a fully differential input capability for the
channel. The common-mode range for these differential inputs
is from GND to VDD. The reference input is unbuffered and,
therefore, excessive R-C source impedances will introduce gain
errors. The reference voltage REFIN (REFIN(+) – REFIN(–)) is
2.5 V nominal, but the AD7791 is functional with reference
voltages from 0.1 V to VDD. In applications where the excitation
(voltage or current) for the transducer on the analog input also
drives the reference voltage for the part, the effect of the low
frequency noise in the excitation source will be removed
because the application is ratiometric. If the AD7791 is used
in a nonratiometric application, a low noise reference should
be used.
Recommended 2.5 V reference voltage sources for the AD7791
include the ADR381 and ADR391, which are low noise, low
power references. In a system that operates from a 2.5 V power
supply, the reference voltage source will require some head-
room. In this case, a 2.048 V reference such as the ADR380 can
be used, requiring only 300 mV of headroom. Also note that the
reference inputs provide a high impedance, dynamic load.
Because the input impedance of each reference input is
dynamic, resistor/ capacitor combinations on these inputs can
cause dc gain errors, depending on the output impedance of the
source that is driving the reference inputs.
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相关代理商/技术参数 |
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| EVAL-AD7792EBZ | 功能描述:BOARD EVALUATION FOR AD7792 RoHS:是 类别:编程器，开发系统 >> 评估板 - 模数转换器 (ADC) 系列:- 产品培训模块:Obsolescence Mitigation Program 标准包装:1 系列:- ADC 的数量:1 位数:12 采样率（每秒）:94.4k 数据接口:USB 输入范围:±VREF/2 在以下条件下的电源（标准）:- 工作温度:-40°C ~ 85°C 已用 IC / 零件:MAX11645 已供物品:板，软件 |
| EVAL-AD7792EBZ1 | 制造商:AD 制造商全称:Analog Devices 功能描述:3-Channel, Low Noise, Low Power, 16-/24-Bit ?￡-?? ADC with On-Chip In-Amp and Reference |
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| EVAL-AD7793EBZ | 功能描述:BOARD EVALUATION FOR AD7793 RoHS:是 类别:编程器，开发系统 >> 评估板 - 模数转换器 (ADC) 系列:- 产品培训模块:Obsolescence Mitigation Program 标准包装:1 系列:- ADC 的数量:1 位数:12 采样率（每秒）:94.4k 数据接口:USB 输入范围:±VREF/2 在以下条件下的电源（标准）:- 工作温度:-40°C ~ 85°C 已用 IC / 零件:MAX11645 已供物品:板，软件 |
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