参数资料
型号: AD7653ACPZ
厂商: Analog Devices Inc
文件页数: 9/28页
文件大小: 0K
描述: IC ADC 16BIT UNIPOLAR 48LFCSP
标准包装: 1
系列: PulSAR®
位数: 16
采样率(每秒): 1M
数据接口: 串行,并联
转换器数目: 1
功率耗散(最大): 145mW
电压电源: 模拟和数字
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 48-VFQFN 裸露焊盘,CSP
供应商设备封装: 48-LFCSP-VQ(7x7)
包装: 托盘
输入数目和类型: 2 个伪差分,单极
配用: EVAL-AD7653CBZ-ND - BOARD EVALUATION FOR AD7653
AD7653
TYPICAL CONNECTION DIAGRAM
when the switches are opened, the input impedance is limited to
C1. R1 and C2 make a 1-pole low-pass filter that reduces
undesirable aliasing effects and limits the noise.
Figure 22 shows a typical connection diagram for the AD7653.
Analog Input
When the source impedance of the driving circuit is low, the
AD7653 can be driven directly. Large source impedances will
significantly affect the ac performance, especially total
harmonic distortion.
Figure 23. Equivalent Analog Input Circuit
shows an equivalent circuit of the input structure of
the AD7653.
The two diodes, D1 and D2, provide ESD protection for the
analog inputs IN and INGND. Care must be taken to ensure
that the analog input signal never exceeds the supply rails by
more than 0.3 V. This will cause these diodes to become
forward-biased and start conducting current. These diodes can
handle a forward-biased current of 100 mA maximum. For
instance, these conditions could eventually occur when the
input buffer’s (U1) supplies are different from AVDD. In such a
case, an input buffer with a short-circuit current limitation can
be used to protect the part.
Driver Amplifier Choice
Although the AD7653 is easy to drive, the driver amplifier needs
to meet the following requirements:
The driver amplifier and the AD7653 analog input circuit
must be able to settle for a full-scale step of the capacitor
array at a 16-bit level (0.0015%). In the amplifier’s data
sheet, settling at 0.1% to 0.01% is more commonly
specified. This could differ significantly from the settling
time at a 16-bit level and should be verified prior to driver
selection. The tiny op amp AD8021, which combines
ultralow noise and high gain-bandwidth, meets this settling
time requirement even when used with gains up to 13.
C2
R1
D1
D2
C1
IN
OR INGND
AGND
AVDD
02966-0-008
The noise generated by the driver amplifier needs to be
kept as low as possible in order to preserve the SNR and
transition noise performance of the AD7653. The noise
coming from the driver is filtered by the AD7653 analog
input circuit 1-pole low-pass filter made by R1 and C2 or
by the external filter, if one is used.
This analog input structure allows the sampling of the different-
tial signal between IN and INGND. Unlike other converters,
INGND is sampled at the same time as IN. By using this differ-
ential input, small signals common to both inputs are rejected.
For instance, by using INGND to sense a remote signal ground,
ground potential differences between the sensor and the local
ADC ground are eliminated.
The driver needs to have a THD performance suitable to
that of the AD7653.
The AD8021 meets these requirements and is appropriate for
almost all applications. The AD8021 needs a 10 pF external
compensation capacitor that should have good linearity as an
NPO ceramic or mica type.
During the acquisition phase, the impedance of the analog input
IN can be modeled as a parallel combination of capacitor C1
and the network formed by the series connection of R1 and C2.
C1 is primarily the pin capacitance. R1 is typically 168 and is
a lumped component made up of some serial resistors and the
on resistance of the switches. C2 is typically 60 pF and is mainly
the ADC sampling capacitor. During the conversion phase,
The AD8022 could also be used if a dual version is needed and
gain of 1 is present. The AD829 is an alternative in applications
where high frequency (above 100 kHz) performance is not
required. In gain of 1 applications, it requires an 82 pF
compensation capacitor. The AD8610 is an option when low
bias current is needed in low frequency applications.
Rev. A | Page 17 of 28
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