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1、24-Bit 电容数字转换器电容数字转换器 带温度传感器带温度传感器 AD7745/AD7746 Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its
2、 use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U
3、.S.A. Tel: 781.329.4700 Fax: 781.461.3113 2005 Analog Devices, Inc. All rights reserved. FEATURES 电容数字转换器电容数字转换器 单芯片解决方案新标准 传感器单端或差分输入接口 分辨率低至4aF（最多21位有效位） 精度：4fF 线性度：0.01% 共模(不改变)电容最大可达 单芯片解决方案新标准 传感器单端或差分输入接口 分辨率低至4aF（最多21位有效位） 精度：4fF 线性度：0.01% 共模(不改变)电容最大可达17 pF 满量程(改变)电容范围满量程(改变)电容范围 4 pF 最大容忍对
4、地寄生电容可达最大容忍对地寄生电容可达60 pF 更新速率更新速率: 10 Hz 至 至 90 Hz 在16Hz处同时抑制50Hz和60Hz 片上温度传感器 在16Hz处同时抑制50Hz和60Hz 片上温度传感器 分辨率 分辨率: 0.1C, 精度精度: 2C 电压输入通道 内部时钟振荡器 电压输入通道 内部时钟振荡器 2线串行接口线串行接口 (兼容兼容I2C) 电源 单电源 电源 单电源2.7 V 5.25 V 电流消耗电流消耗0.7 mA 工作温度：工作温度： 40C to +125C 16管脚管脚 TSSOP 封装封装 APPLICATIONS 汽车、工业、医疗器械汽车、工业、医疗器械
5、压力测量 位置传感 压力测量 位置传感 器 液位传感器 器 液位传感器 流量计 湿度传感器 杂质检测 流量计 湿度传感器 杂质检测 GENERAL DESCRIPTION AD7745/AD7746是一个高分辨率- 型电容数字转换器 (CDC). 被测电容与设备输入管脚直接连接. 该结构固有高分 辨率(24位无失码，最高21位有效分辨率)、高线性度 (0.01%)和高精度 (工厂校准4 fF ). AD7745/AD7746 电容 输入范围 4 pF (改变), 同时可接受最大17pF共模电容(不可 变), 可以通过一个片上数字电容转换器(CAPDAC)平衡. The AD7745 has o
6、ne capacitance input channel, while the AD7746 has two channels. Each channel can be configured as single-ended or differential. The AD7745/AD7746 are designed for floating capacitive sensors. For capacitive sensors with one plate connected to ground, the AD7747 is recommended. The parts have an on-
7、chip temperature sensor with a resolution of 0.1C and accuracy of 2C. 片上电压基准和片 上时钟发生器省去了在电容传感器应用中需要任何外部元 件.该器件有一个标准电压输入，当与差分基准电压输入结 合可轻松实现一个外部温度传感器，如RTD ，热敏电阻或 二极管。 The AD7745/AD7746 have a 2-wire, I2C-compatible serial interface. Both parts can operate with a single power supply from 2.7 V to 5.25
8、V. They are specified over the automotive temperature range of 40C to +125C and are housed in a 16-lead TSSOP package. FUNCTIONAL BLOCK DIAGRAMS DIGITAL FILTER 24-BIT - MODULATOR CLOCK GENERATOR MUX TEMP SENSOR CAP DAC CAP DAC VOLTAGE REFERENCE CONTROL LOGIC CALIBRATION AD7745 VDD REFIN(+) REFIN()GN
9、D SDA SCL RDY VIN(+) VIN() CIN1(+) CIN1() EXCA EXCB 05468-001 I2C SERIAL INTERFACE EXCITATION Figure 1. DIGITAL FILTER 24-BIT - MODULATOR MUX TEMP SENSOR CAP DAC CAP DAC VOLTAGE REFERENCE CONTROL LOGIC CALIBRATION AD7746 VDD REFIN(+) REFIN()GND SDA SCL RDY VIN(+) VIN() CIN1(+) CIN1() CIN2(+) CIN2()
10、EXC1 EXC2 05468-002 CLOCK GENERATOR I2C SERIAL INTERFACE EXCITATION Figure 2. AD7745/AD7746 Rev. 0 | Page 2 of 28 TABLE OF CONTENTS Specifications.3 Timing Specifications.5 Absolute Maximum Ratings6 Pin Configurations and Function Descriptions.7 Typical Performance Characteristics.8 Output Noise and
11、 Resolution Specifications11 Serial Interface 12 Read Operation.12 Write Operation12 AD7745/AD7746 Reset.13 General Call.13 Register Descriptions.14 Status Register.15 Cap Data Register.15 VT Data Register15 Cap Set-Up Register.16 VT Set-Up Register16 EXC Set-Up Register17 Configuration Register18 C
12、ap DAC A Register.19 Cap DAC B Register.19 Cap Offset Calibration Register19 Cap Gain Calibration Register 19 Volt Gain Calibration Register. 19 Circuit Description. 20 Overview . 20 Capacitance-to-Digital Converter . 20 Excitation Source 20 CAPDAC. 21 Single-Ended Capacitive Input. 21 Differential
13、Capacitive Input 21 Parasitic Capacitance to Ground 22 Parasitic Resistance to Ground. 22 Parasitic Parallel Resistance 22 Parasitic Serial Resistance. 23 Capacitive Gain Calibration . 23 Capacitive System Offset Calibration 23 Internal Temperature Sensor 23 External Temperature Sensor. 24 Voltage I
14、nput. 24 VDD Monitor 24 Typical Application Diagram 24 Outline Dimensions. 25 Ordering Guide 25 REVISION HISTORY 4/05Revision 0: Initial Version AD7745/AD7746 Rev. 0| Page 3 of 28 SPECIFICATIONS VDD = 2.7 V to 3.6 V or 4.75 V to 5.25 V; GND = 0 V; EXC = 32 kHz; EXC = VDD/2; 40C to +125C, unless othe
15、rwise noted. Table 1. ParameterMin Typ Max Unit Test Conditions/Comments 电容输入 4.096 pF1工厂校准 0.01 % of FSR 24 Bit Conversion time 62 ms 16.5 Bit Conversion time = 62 ms, see Table 5 19 Bit Conversion time = 62 ms, see Table 5 2 aF/Hz See Table 5 4fF125C, VDD = 5 V, after offset calibration 转换输入范围 积分非
16、线性(INL)2 ?无失码2 分辨率, p-p 有效分辨率 输出噪声, rms 绝对误差3 偏移误差2, 432aF1 After system offset calibration, Excluding effect of noise4 1pF 1 aF/C 0.02 0.08 % of FS 25C, VDD = 5 V 282624ppm of FS/C 60 pF See Figure 9 and Figure 10 0.3 1 fF/V 65 dB 50 Hz 1%, conversion time = 62 ms 55 dB 60 Hz 1%, conversion time = 62 ms 系统失调校准范围2 失调温度漂移 增益误差5 增益温度漂移2 允许对地电容2 电源抑制 常模抑制 Channel-to-Channel Isolation 70 dB AD7746 only CAPDAC 17 21 pF 164fF7
