参数资料
型号: AD7495BR-REEL
厂商: Analog Devices Inc
文件页数: 7/25页
文件大小: 0K
描述: IC ADC 12BIT SRL LP W/REF 8-SOIC
产品变化通告: AD7495 Obsolescence 15/Apr/2011
标准包装: 2,500
位数: 12
采样率(每秒): 1M
数据接口: DSP,MICROWIRE?,QSPI?,串行,SPI?
转换器数目: 1
功率耗散(最大): 10.5mW
电压电源: 单电源
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 8-SOIC(0.154",3.90mm 宽)
供应商设备封装: 8-SOIC
包装: 带卷 (TR)
输入数目和类型: 1 个单端,单极
AD7475/AD7495
Rev. B | Page 14 of 24
TYPICAL CONNECTION DIAGRAM
Figure 13 and Figure 15 show typical connection diagrams for
the AD7475 and AD7495, respectively. In both setups the GND
pin is connected to the analog ground plane of the system. In
Figure 13, REF IN is connected to a decoupled 2.5 V supply
from a reference source, the AD780, to provide an analog input
range of 0 V to 2.5 V. Although the AD7475 is connected to a
VDD of 5 V, the serial interface is connected to a 3 V micro-
processor. The VDRIVE pin of the AD7475 is connected to the
same 3 V supply of the microprocessor to allow a 3 V logic
interface (see the Digital Inputs section.) In Figure 15, the REF
OUT pin of the AD7495 is connected to a buffer and then
applied to a level-shifting circuit used on the analog input to
allow a bipolar signal to be applied to the AD7495. A minimum
100 nF capacitance is required on the REF OUT pin to GND.
The conversion result from both ADCs is output in a 16-bit
word with four leading zeros followed by the MSB of the 12-bit
result. For applications where power consumption is of concern,
the power-down modes should be used between conversions or
bursts of several conversions to improve power performance.
See the Operating Modes section for more information.
VDD
VIN
GND
5V
SUPPLY
2.5V
AD780
3V
SUPPLY
AD7475
0V TO
2.5V
INPUT
SDATA
μC/μP
SCLK
SERIAL
INTERFACE
0.1
μF
(MIN)
VDRIVE
REF IN
0.1
μF
10
μF
0.1
μF
10
μF
CS
01684-B
-013
Figure 13. AD7475 Typical Connection Diagram
Analog Input
Figure 14 shows an equivalent circuit of the analog input
structure of the AD7475/AD7495. The D1 and D2 diodes
provide ESD protection for the analog inputs. Care must be
taken to ensure that the analog input signal never exceeds the
supply rails by more than 200 mV. This causes these diodes to
become forward-biased and start conducting current into the
substrate. The maximum current these diodes can conduct
without causing irreversible damage to the part is 20 mA.
The capacitor C1 in Figure 14 is typically about 4 pF and can
primarily be attributed to pin capacitance. The resistor R1 is a
lumped component made up of the on resistance of a switch.
This resistor is typically about 100 Ω. The capacitor C2 is
the ADC sampling capacitor and has a capacitance of 16 pF,
typically. For ac applications, it is recommended to remove
high frequency components from the analog input signal
using an RC low-pass filter on the relevant analog input pin. In
applications where harmonic distortion and signal-to-noise
ratio are critical, the analog input should be driven from a low
impedance source. Large source impedances significantly affect
the ac performance of the ADC. This may necessitate the use of
an input buffer amplifier. The choice of the op amp is a function
of the particular application.
R1
VIN
C2
16pF
D1
D2
C1
4pF
VDD
CONVERSION PHASE: SWITCH OPEN
TRACK PHASE: SWITCH CLOSED
01684-B
-014
Figure 14. Equivalent Analog Input Circuit
VDD
VIN
GND
5V
SUPPLY
3V
SUPPLY
AD7495
0V TO
2.5V
INPUT
SDATA
μC/μP
SCLK
SERIAL
INTERFACE
0.1
μF
(MIN)
VDRIVE
REF OUT
0.1
μF
10
μF
0.1
μF
10
μF
R
3R
R
V
0V
V
CS
01684-B-015
Figure 15. AD7495 Typical Connection Diagram
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