参数资料
型号: AD8224ACPZ-WP
厂商: Analog Devices Inc
文件页数: 18/28页
文件大小: 0K
描述: IC AMP INST JFET R-R LP 16LFCSP
标准包装: 64
放大器类型: 仪表
电路数: 2
输出类型: 满摆幅
转换速率: 2 V/µs
-3db带宽: 1.5MHz
电流 - 输入偏压: 25pA
电压 - 输入偏移: 300µV
电流 - 电源: 750µA
电流 - 输出 / 通道: 15mA
电压 - 电源,单路/双路(±): 4.5 V ~ 36 V,±2.25 V ~ 18 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 16-VQFN 裸露焊盘,CSP
供应商设备封装: 16-LFCSP-VQ
包装: 托盘 - 晶粒
配用: AD8224-EVALZ-ND - BOARD EVALUATION AD8224
Data Sheet
AD8224
Rev. C | Page 25 of 28
AD8224
(DIFF OUT)
100pF
NPO
5%
100pF
NPO
5%
1000pF
–IN
+IN
0.1F
10F
0.1F
10F
–12V
+12V
1k
+
IN+
VDD
GND
REF
10F
X5R
AD7688
IN–
0.1F
+5V
ADR435
GND
VIN
VOUT
0.1F
+12V
0.1F
+5V REF
+IN2
REF2
+5V REF
+OUT
–OUT
806
2.7nF
806
06286-
066
Figure 65. Driving a Differential ADC
DRIVING A DIFFERENTIAL INPUT ADC
The AD8224 can be configured in differential output mode
to drive a differential ADC. Figure 65 illustrates several of the
concepts.
First Antialiasing Filter
The 1 k resistor, 1000 pF capacitor, and 100 pF capacitors in
front of the in-amp form a 76 kHz filter. This is the first of two
antialiasing filters in the circuit and helps to reduce the noise of
the system. The 100 pF capacitors protect against common-
mode RFI signals. Note that they are 5% COG/NPO types.
These capacitors match well over time and temperature,
which keeps the CMRR of the system high over frequency.
Second Antialiasing Filter
An 806 resistor and a 2.7 nF capacitor are located between
each AD8224 output and ADC input. These components create
a 73 kHz low-pass filter for another stage of antialiasing
protection.
These four elements also isolate the ADC from loading the
AD8224. The 806 resistor shields the AD8224 from the
switched capacitor input of the ADC, which looks like a time-
varying load. The 2.7 nF capacitor provides a charge to the
switched capacitor front end of the ADC. If the application
requires a lower frequency antialiasing filter, increase the value
of the capacitor rather than the resistor.
The 806 resistors can also protect an ADC from overvoltages.
Because the AD8224 runs on wider supply voltages than a
typical ADC, there is a possibility of overdriving the ADC. This
is not an issue with a PulSAR converter, such as the AD7688.
Its input can handle a 130 mA overdrive, which is much higher
than the short-circuit limit of the AD8224.
However, other converters have less robust inputs and may need
the added protection.
Reference
The ADR435 supplies a reference voltage to both the ADC and
the AD8224. Because REF2 on the AD8224 is grounded, the
common-mode output voltage is precisely half the reference
voltage, exactly where it needs to be for the ADC.
DRIVING CABLING
All cables have a certain capacitance per unit length, which
varies widely with cable type. The capacitive load from the cable
may cause peaking in the AD8224 output response. To reduce
peaking, use a resistor between the AD8224 and the cable.
Because cable capacitance and desired output response vary
widely, this resistor is best determined empirically. A good
starting point is 50 .
The AD8224 operates at a low enough frequency that
transmission line effects are rarely an issue; therefore, the
resistor need not match the characteristic impedance of
the cable.
AD8224
(DIFF OUT)
AD8224
(SINGLE OUT)
06286-
067
Figure 66. Driving a Cable
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