参数资料
型号: AD7785BRUZ-REEL
厂商: Analog Devices Inc
文件页数: 24/32页
文件大小: 0K
描述: IC ADC 20BIT 3CH LN LP 16-TSSOP
标准包装: 2,500
位数: 20
采样率(每秒): 470
数据接口: MICROWIRE?,QSPI?,串行,SPI?
转换器数目: 1
电压电源: 模拟和数字
工作温度: -40°C ~ 105°C
安装类型: 表面贴装
封装/外壳: 16-TSSOP(0.173",4.40mm 宽)
供应商设备封装: 16-TSSOP
包装: 带卷 (TR)
输入数目和类型: 3 个差分,单极;3 个差分,双极
配用: EVAL-AD7785EBZ-ND - BOARD EVALUATION FOR AD7785
AD7785
Rev. 0 | Page 30 of 32
TEMPERATURE MEASUREMENT USING AN RTD
To optimize a 3-wire RTD configuration, two identically
matched current sources are required. The AD7785, which
contains two well-matched current sources, is ideally suited to
these applications. One possible 3-wire configuration is shown
in Figure 21. In this 3-wire configuration, the lead resistances
result in errors if only one current is used, as the excitation
current flows through RL1, developing a voltage error between
AIN1(+) and AIN1(–). In the scheme outlined, the second RTD
current source is used to compensate for the error introduced
by the excitation current flowing through RL1. The second RTD
current flows through RL2. Assuming RL1 and RL2 are equal
(the leads would normally be of the same material and of equal
length), and IOUT1 and IOUT2 match, the error voltage across
RL2 equals the error voltage across RL1, and no error voltage
is developed between AIN1(+) and AIN1(–). The voltage is
developed twice across RL3. However, because this is a
common- mode voltage, it does not introduce errors. The
reference voltage for the AD7785 is also generated using one of
these matched current sources. It is developed using a precision
resistor and applied to the differential reference pins of the
ADC. This scheme ensures that the analog input voltage span
remains ratiometric to the reference voltage. Any errors in the
analog input voltage due to the temperature drift of the excita-
tion current are compensated by the variation of the reference
voltage.
06
72
1-
0
21
DOUT/RDY
DIN
SCLK
CS
DVDD
SERIAL
INTERFACE
AND
CONTROL
LOGIC
AD7785
IOUT1
REFIN(+)
REFIN(–)
AVDD
GND
BAND GAP
REFERENCE
INTERNAL
CLOCK
CLK
GND
AVDD
IN-AMP
BUF
REFIN(+) REFIN(–)
AIN1(+)
AIN1(–)
RREF
IOUT2
RL2
RL1
RTD
RL3
Σ-Δ
ADC
Figure 21. RTD Application Using the AD7785
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