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| 型号： | EVAL-AD7643CBZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 11/28页 |
| 文件大小： | 0K |
| 描述： | BOARD EVALUATION FOR AD7643 |
| 标准包装： | 1 |
| 系列： | PulSAR® |
| ADC 的数量： | 1 |
| 位数： | 18 |
| 采样率（每秒）： | 1.25M |
| 数据接口： | 串行，并联 |
| 输入范围： | ±VREF |
| 在以下条件下的电源（标准）： | 65mW @ 1.25MSPS |
| 工作温度： | -40°C ~ 85°C |
| 已用 IC / 零件： | AD7643 |
| 已供物品： | 板 |
| 相关产品： | AD7643BCPZRL-ND - IC ADC 18BIT DIFF W/REF 48-LFCSP AD7643BCPZ-ND - IC ADC 18BIT DIFF W/REF 48LFCSP AD7643BSTZ-ND - IC ADC 18BIT DIFFER W/REF 48LQFP AD7643BSTZRL-ND - IC ADC 18BIT DIFFER W/REF 48LQFP |
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AD7643
Rev. 0 | Page 19 of 28
Internal Reference (PDBUF = Low, PDREF = Low)
To use the internal reference, the PDREF and PDBUF inputs
must both be low. This produces a 1.2 V band gap output on
REFBUFIN, which is amplified by the internal buffer and
results in a 2.048 V reference on the REF pin.
The internal reference is temperature compensated to 2.048 V ±
10 mV. The reference is trimmed to provide a typical drift of
The output resistance of REFBUFIN is 6.33 kΩ (minimum)
when the internal reference is enabled. It is necessary to
decouple this with a ceramic capacitor greater than 100 nF.
Therefore, the capacitor provides an RC filter for noise reduction.
Because the output impedance of REFBUFIN is typically
6.33 kΩ, relative humidity (among other industrial contaminates)
can directly affect the drift characteristics of the reference.
Typically, a guard ring is used to reduce the effects of drift
under such circumstances. However, because the AD7643 has a
fine lead pitch, guarding this node is not practical. Therefore, in
these industrial and other types of applications, it is recommended
to use a conformal coating, such as Dow Corning 1-2577 or
HumiSeal 1B73.
External 1.2 V Reference and Internal Buffer (PDBUF =
Low, PDREF = High)
To use an external reference along with the internal buffer,
PDREF should be high and PDBUF should be low. This powers
down the internal reference and allows an external 1.2 V
reference to be applied to REFBUFIN, producing 2.048 V
(typically) on the REF pin.
External 2.5 V Reference (PDBUF = High, PDREF = High)
To use an external 2.5 V reference directly on the REF pin,
PDREF and PDBUF should both be high.
For improved drift performance, an external reference, such as
using the external voltage reference are:
The SNR and dynamic range improvement (about 1.7 dB)
resulting from the use of a reference voltage very close to
the supply (2.5 V) instead of a typical 2.048 V reference
when the internal reference is used. This is calculated by
=
50
.
2
048
.
2
log
20
SNR
The power savings when the internal reference is powered
down (PDREF high).
PDREF and PDBUF power down the internal reference and
the internal reference buffer, respectively. The input current
of PDREF and PDBUF should never exceed 20 mA. This can
occur when the driving voltage is above AVDD (for instance, at
power-up). In this case, a 125 Ω series resistor is recommended.
Reference Decoupling
Whether using an internal or external reference, the AD7643
voltage reference input (REF) has a dynamic input impedance;
therefore, it should be driven by a low impedance source with
efficient decoupling between the REF and REFGND inputs.
This decoupling depends on the choice of the voltage reference
but usually consists of a low ESR capacitor connected to REF
and REFGND with minimum parasitic inductance.
A 10 μF (X5R, 1206 size) ceramic chip capacitor (or 47 μF
tantalum capacitor) is appropriate when using either the
internal reference or one of the recommended reference voltages.
The placement of the reference decoupling is also important to
the performance of the AD7643. The decoupling capacitor
should be mounted on the same side as the ADC right at the
REF pin with a thick PCB trace. The REFGND should also connect
to the reference decoupling capacitor with the shortest distance.
For applications that use multiple AD7643 devices, it is more
effective to use an external reference with the internal reference
buffer to buffer the reference voltage. However, because the
reference buffers are not unity gain, ratiometric, simultaneously
sampled designs should use an external reference and external
same reference level for all converters.
The voltage reference temperature coefficient (TC) directly
impacts full scale; therefore, in applications where full-scale
accuracy matters, care must be taken with the TC. For instance,
a ±4 ppm/°C TC of the reference changes full scale by ±1 LSB/°C.
Note that VREF can be increased to AVDD + 0.1 V. Because the
input range is defined in terms of VREF, this would essentially
increase the range to 0 V to 2.8 V with an AVDD = 2.7 V.
Temperature Sensor
The TEMP pin measures the temperature of the AD7643. To
improve the calibration accuracy over the temperature range,
the output of the TEMP pin is applied to one of the inputs of
the analog switch (such as, ADG779), and the ADC itself is
used to measure its own temperature. This configuration is
shown in Figure 28.
ADG779
AD8021
CC
ANALOG INPUT
(UNIPOLAR)
AD7643
IN+
TEMPERATURE
SENSOR
TEMP
06
02
4-
0
2
8
Figure 28. Use of the Temperature Sensor
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| EVAL-AD7643EDZ | 功能描述:BOARD EVAL FOR AD7643 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-AD7650CB | 制造商:Analog Devices 功能描述:EVAL BD EVAL BD AD765X/AD766X/AD767X - Bulk |
| EVAL-AD7650CBZ | 功能描述:BOARD EVALUATION FOR AD7650 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-AD7650EDZ | 功能描述:BOARD EVAL FOR AD7650 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-AD7651CB | 制造商:Analog Devices 功能描述:DEV TOOLS, 16BIT 100KSPS SAR UNIPOLAR ADC W/ REF - Bulk |
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