1、24-Bit 电容数字转换器带温度传感器AD7745/AD7746Rev. 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 use. Specificat
2、ions 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.S.A. Tel: 781.3
3、29.4700 Fax: 781.461.3113 2005 Analog Devices, Inc. All rights reserved. FEATURES 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 17 pF满量程(改变)电容范围 4 pF 最 大 容 忍 对 地 寄 生 电 容 可 达 60 pF 更 新 速率: 10 Hz 至 90 Hz 在 16Hz处 同 时 抑制5 0Hz和 60Hz片上温度传感器 分 辨 率 : 0.1C, 精度: 2C 电 压输入通道内部时钟振
4、荡器2线串行接口 (兼容I 2C) 电源单 电源2.7 V 5.25 V 电流消耗0.7 mA 工 作温度： 40C to +125C 16管脚 TSSOP 封装APPLICATIONS 汽车、工业、医疗器械 压 力 测量位置传感 器液 位 传 感 器 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
5、 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 one 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
6、plate connected to ground, the AD7747 is recommended. The parts have an on-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 inter
7、face. Both parts can operate with a single power supply from 2.7 V to 5.25 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 DIGITALFILTER24-BIT -MODULATORCLOCKGENERATORMUXTEMPSENSORCAP DACCAP DACVOLTAGERE
8、FERENCECONTROL LOGICCALIBRATIONAD7745VDDREFIN(+) REFIN() GNDSDASCLRDYVIN(+)VIN()CIN1(+)CIN1()EXCAEXCB05468-001I2CSERIALINTERFACEEXCITATIONFigure 1. DIGITALFILTER24-BIT -MODULATORMUXTEMPSENSORCAP DACCAP DACVOLTAGEREFERENCECONTROL LOGICCALIBRATIONAD7746VDDREFIN(+) REFIN() GNDSDASCLRDYVIN(+)VIN()CIN1(+
9、)CIN1()CIN2(+)CIN2()EXC1EXC205468-002CLOCKGENERATORI2CSERIALINTERFACEEXCITATIONFigure 2.AD7745/AD7746 Rev. 0 | Page 2 of 28 TABLE OF CONTENTS Specifications. 3Timing Specifications. 5Absolute Maximum Ratings 6Pin Configurations and Function Descriptions . 7Typical Performance Characteristics . 8Outp
10、ut Noise and Resolution Specifications 11Serial Interface 12Read Operation. 12Write Operation 12AD7745/AD7746 Reset . 13General Call. 13Register Descriptions . 14Status Register . 15Cap Data Register. 15VT Data Register 15Cap Set-Up Register. 16VT Set-Up Register 16EXC Set-Up Register 17Configuratio
11、n Register 18Cap DAC A Register. 19Cap DAC B Register. 19Cap Offset Calibration Register 19Cap Gain Calibration Register 19Volt Gain Calibration Register . 19Circuit Description. 20Overview . 20Capacitance-to-Digital Converter . 20Excitation Source 20CAPDAC . 21Single-Ended Capacitive Input. 21Diffe
12、rential Capacitive Input 21Parasitic Capacitance to Ground 22Parasitic Resistance to Ground. 22Parasitic Parallel Resistance 22Parasitic Serial Resistance . 23Capacitive Gain Calibration . 23Capacitive System Offset Calibration 23Internal Temperature Sensor 23External Temperature Sensor . 24Voltage
13、Input . 24VDD Monitor 24Typical Application Diagram 24Outline Dimensions . 25Ordering Guide 25REVISION HISTORY 4/05Revision 0: Initial Version AD7745/AD7746Rev. 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 otherwi
14、se noted. Table 1. Parameter Min Typ Max Unit Test Conditions/Comments电 容 输 入 4.096 pF1 工 厂校准0.01 % of FSR24 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
15、 分 非 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, 4 32 aF1 After system offset calibration, Excluding effect of noise41pF1 aF/C 0.02 0.08 % of FS 25C, VDD = 5 V 28 26 24 ppm of FS/C60 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%, conversi
16、on 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 CAPDAC17 21 pF 164 fF 7-bit CAPDAC满 量程分 辨 率 6温 度漂移 2 24 26 28 ppm of FS/CEXCITATION32 kHz频 率电 容电压 VDD/8 V 通 过数字接口可配置 VDD/4 V VDD 3/8 VVDD/2 V 通 过电容平均直流电压 30 M) VDD 3 V: IGND 50 M) VDD 2.
17、7 V: IGND 100 M) A higher leakage current to ground results in a gain error, an offset error, and a nonlinearity error. See the typical performance characteristics shown in Figure 12 and Figure 13. 寄生并联电阻 DATACDCEXCCINRP05468-022CXFigure 38. Parasitic Parallel Resistance AD7745/AD7746 CDC 测量 EXC 管脚和
18、 CIN管脚 间电荷转移 . Any resistance connected in parallel to the measured capacitance CX (see Figure 38), such as the parasitic resistance of the sensor, also transfers charge. Therefore, the parallel resistor is seen as an additional capacitance in the output data.等效并联电容(或者并联电 阻造成的错误) 可以近似计算41=EXCPPFRCWh
19、ere RP is the parallel resistance and CEXC is the excitation frequency. See the typical performance characteristics shown in Figure 14. AD7745/AD7746Rev. 0| Page 23 of 28 寄生串联电阻 DATACDCEXCRS1CINRS2CX05468-023Figure 39. Parasitic Serial Resistance The AD7745/AD7746 CDC result is affected by a resista
20、nce in series with the measured capacitance. The total serial resistance, which refers to RS1 + RS2 on Figure 39, should be less than 1 k for the specified performance. See typical performance charac-teristics shown in Figure 15. 电容增益校准 The AD7745/AD7746 gain is factory calibrated for the full scale
21、 of 4.096 pF in the production for each part individually. The factory gain coefficient is stored in a one-time programmable (OTP) memory and is copied to the capacitive gain register at power-up or after reset. 增益可以通过外部连接一个满量程电容执行电容校准模式更改，或者向电容增益校准寄存器写入一个用户值更改。这种改变只是暂时性的，在上电或者复位后工厂校准系数将会被重新装载回来。 Th
22、e part is tested and specified only for use with the default factory calibration coefficient. 电容系统失调校准 The capacitive offset is dominated by the parasitic offset in the application, such as the initial capacitance of the sensor, any parasitic capacitance of tracks on the board, and the capacitance o
23、f any other connections between the sensor and the CDC. Therefore, the AD7745/AD7746 are not factory calibrated for capacitive offset. It is the users responsibility to calibrate the system capacitance offset in the application. 任何输入失调电容超过1 pF应该首先使用片上CAPDACs补偿 . 在 1 pF 之间的小失调电容可以通过电容失调校准寄存器补偿. 调 整失调
24、的一种方法是连接一个零电容到输入端然后执行电容失调校准模式. The calibration sets the midpoint of the 4.096 pF range (that is, Output Code 0x800000) to that zero-scale input. 另一种方法是计算并写入失调校 准寄存器值, LSB 值是 31.25 aF (4.096 pF/217). 失调校准寄存器在上电和复位后重新 加 载默认值.因此，如果不是每次上电都需要失调校准，校准系数值应该被主控制器存储并作为 AD7745/AD7746 设置的一部分被加载. 在 AD7746中，该寄存器被
25、两个电容通道共享。如果电容融到需要独立的失调校准，主控制器软件应该在独立通道执行失调校准后读取AD7746电容失调校准寄存器值并在每次不同通道执行转换前加载该值. 内 部 温 度传感器 DIGITALFILTERANDSCALING24-BIT -MODULATORCLOCKGENERATORINTERNAL TEMPERATURE SENSOR05468-040VOLTAGEREFERENCEDATAIN IVBEVDDFigure 40. Internal Temperature Sensor AD7745/AD7746 使用的温度测量方法是在两个不同电 流下测量 晶体管V BE 压 差(
26、see Figure 40). VBE 改变与温度成线性关系可以表示为)ln()( NqKTnVfBE= where: K ：波尔兹曼常数(1.3 8 1023). T ：开尔文绝对温度. q ：电子电量(1.6 1019 C). N ：两 个 电流比值. nf ：热敏二极管理想因子. AD7745/AD7746 使 用 一个片上晶体管测量硅芯片内部温度 . - ADC 将 VBE 压差转换为数字量, 数据使用工厂校准系数扩展, 因此输入代码与 温度成正比t: () 40962048=CodeCeTemperaturThe AD7745/AD7746 has a low power consu
27、mption resulting in only a small effect due to the part self-heating (less than 0.5C at VDD = 5 V). AD7745/AD7746 Rev. 0 | Page 24 of 28 如 果 电容传感器可以被认为在与AD77 45/AD7746 芯片具有相同温度, 内部温度传感器可以被作为系统温度传感 器 . 这 意味着整个系统温度漂移补偿可以基于AD774 5 / AD7746内部温度传感器 ， 而 不需要任何额外的外部元件See the typical performance characterist
28、ics in Figure 18. 外部温度传感器 DIGITALFILTERANDSCALING24-BIT -MODULATORCLOCKGENERATOREXTERNALTEMPERATURESENSOR05468-041VOLTAGEREFERENCEDATAI . N IVBEVDDVIN ()VIN (+)RS2RS12N3906Figure 41. Transistor as an External Temperature Sensor The AD7745/AD7746 provide the option of using an external transistor as
29、a temperature sensor in the system. The VBE method, which is similar to the internal temperature sensor method, is used. However, it is modified to compensate for the serial resistance of connections to the sensor. Total serial resistance (RS1 + RS2 in Figure 41) up to 100 is compensated. The VIN()
30、pin must be grounded for proper external temperature sensor operation. The AD7745/AD7746 are factory calibrated for Transistor 2N3906 with the ideality factor nf = 1.008. See the typical performance characteristics shown in Figure 19. 电压输入 DIGITALFILTER24-BIT -MODULATORCLOCKGENERATORANALOG TO DIGITA
31、L CONVERTER(ADC)05468-042VOLTAGEREFERENCEDATAVIN()VIN(+)REFIN()REFIN(+)RREFRTDRTVDDGNDFigure 42. Resistive Temperature Sensor Connected to the Voltage Input The AD7745/AD7746 - core can work as a high resolution (up to 21 ENOB) classic ADC with a fully differential voltage input. The ADC can be used
32、 either with the on-chip high precision, low drift, 1.17 V voltage reference, or an external reference connected to the fully differential reference input pins. The voltage and reference inputs are continuously sampled by a - modulator during the conversion. Therefore, the input source impedance sho
33、uld be kept low. See the application example in Figure 42. VDD 监视器 Along with converting external voltages, the AD7745/AD7746 - ADC can be used for monitoring the VDD voltage. The voltage from the VDD pin is internally attenuated by 6. 典型应用图 DIGITALFILTER24-BIT -MODULATORCLOCKGENERATORMUXTEMPSENSORC
34、AP DACCAP DACEXCITATIONVOLTAGEREFERENCECONTROL LOGICCALIBRATIONAD7745VDDREFIN(+) REFIN()GNDSDASCLRDYVIN(+)VIN()CIN1(+)CIN1()EXCAEXCB05468-008HOSTSYSTEM+0.1F 10F3V/5VPOWER SUPPLYI2CSERIALINTERFACE10k10kFigure 43. Basic Application Diagram for a Differential Capacitive Sensor AD7745/AD7746Rev. 0 | Pag
35、e 25 of 28 OUTLINE DIMENSIONS 16 981PIN 1SEATINGPLANE804.504.404.306.40BSC5.105.004.900.65BSC0.150.051.20MAX0.200.090.750.600.450.300.19COPLANARITY0.10COMPLIANT TO JEDEC STANDARDS MO-153-ABFigure 44. 16-Lead Thin Shrink Small Outline Package TSSOP (RU-16) Dimensions shown in millimeters ORDERING GUI
36、DE Model Temperature Range Package Description Package Option AD7745ARUZ140C to +125C 16-Lead TSSOP RU-16 AD7745ARUZ-REEL140C to +125C 16-Lead TSSOP RU-16 AD7745ARUZ-REEL7140C to +125C 16-Lead TSSOP RU-16 AD7746ARUZ140C to +125C 16-Lead TSSOP RU-16 AD7746ARUZ-REEL140C to +125C 16-Lead TSSOP RU-16 AD
37、7746ARUZ-REEL7140C to +125C 16-Lead TSSOP RU-16 EVAL-AD7746EB Evaluation Board1Z = Pb-free part. AD7745/AD7746 Rev. 0 | Page 26 of 28 NOTES AD7745/AD7746Rev. 0 | Page 27 of 28 NOTES AD7745/AD7746 Rev. 0 | Page 28 of 28 NOTES Purchase of licensed I2C components of Analog Devices or one of its sublice
38、nsed Associated Companies conveys a license for the purchaser under the Philips I2C Patent Rights to use these components in an I2C system, provided that the system conforms to the I2C Standard Specification as defined by Philips. 2005 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. C05468-0-4/05(0)
