Ultra Low Power, 2 Channel, Capacitance Converter for Proximity Sensing AD7150 Preliminary Technical Data FEATURES GENERAL DESCRIPTION Ultra low power 3.3 V, 90 uA Response time 10 ms Adaptive environmental compensation Two independent capacitance input channels Sensor capacitance (CSENS) 0 up to 14 pF Sensitivity to 0.8 fF EMC tested Two modes of operation: Standalone with fixed settings Interfaced to a uC for user-defined settings Two proximity detection output flags The AD7150 delivers a complete signal processing solution for capacitive proximity sensors, featuring an ultra low power converter with fast response time. The AD7150 uses Analog Devices’ capacitance to digital converter (CDC) technology, which combines features important for interfacing to real sensors, such as a high input sensitivity and a high tolerance of both input parasitic ground capacitance and leakage current. The integrated adaptive threshold algorithm compensates for any variations in the sensor capacitance due to environmental factors like humidity and temperature, or changes in the dielectric material over time. 2-wire serial interface (I2C®-compatible) Operating temperature: -40°C to +125°C 10-lead uSOIC package By default, the AD7150 operates in standalone mode using the fixed power up settings and indicates detection on two digital outputs. Alternatively, the AD7150 can be interfaced to a uC via I2C interface, the internal registers can be programmed with user-defined settings and the data and status can be read from the part. APPLICATIONS Proximity sensing Contact-less switching Position detection Level detection The AD7150 operates from a 3.3 V power supply. It is specified over the temperature range of -40°C to +125°C. FUNCTIONAL BLOCK DIAGRAM VDD CSENS1 CIN1 Σ−∆ CDC DIGITAL FILTER SERIAL INTERFACE SCL SDA EXC1 CSENS2 CIN2 MUX AD7150 EXCITATION EXC2 THRESHOLD OUT1 THRESHOLD OUT2 GND Figure 1. Rev. PrD, 8. November 2006 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. 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.S.A. www.analog.com Tel: 781.329.4700 Fax: 781.461.3113 © 2006 Analog Devices, Inc. All rights reserved. Preliminary Technical Data AD7150 TABLE OF CONTENTS Preliminary Specifications............................................................... 3 Sensitivity Registers ................................................................... 13 Timing Specifications....................................................................... 4 Timeout Registers....................................................................... 13 Absolute Maximum Ratings............................................................ 5 Setup Registers............................................................................ 14 Pin Configurations and Function Descriptions ........................... 6 Configuration Register .............................................................. 15 Typical Performance Characteristics ............................................. 7 Power Down Timer Register .................................................... 16 Architecture and Main Features ..................................................... 8 Cap DAC B Registers ................................................................. 16 Overview........................................................................................ 8 Serial Number Registers ............................................................ 16 Capacitance to Digital Converter............................................... 8 Chip ID Registers ....................................................................... 16 CAPDAC ....................................................................................... 8 Serial Interface ................................................................................ 17 Comparator and Threshold Modes............................................ 9 Read Operation .......................................................................... 17 Adaptive Threshold...................................................................... 9 Write Operation.......................................................................... 17 Data Average ................................................................................. 9 AD7150 Reset ............................................................................. 18 Sensitivity .................................................................................... 10 General Call ................................................................................ 18 Hysteresis..................................................................................... 10 Hardware Design Considerations ................................................ 19 Timeout........................................................................................ 10 Overview ..................................................................................... 19 Auto CAPDAC adjustment ....................................................... 10 Parasitic Capacitance to Ground.............................................. 19 Power Down Timer .................................................................... 10 Parasitic Resistance To Ground................................................ 19 Register Descriptions ..................................................................... 11 Parasitic Parallel Resistance ...................................................... 19 Status Register ............................................................................. 12 Parasitic Serial Resistance ......................................................... 20 Data Registers ............................................................................. 12 Input Overvoltage Protection ................................................... 20 Average Registers........................................................................ 12 Input EMC Protection ............................................................... 20 Fixed Threshold Registers ......................................................... 12 Application Examples ................................................................ 21 REVISION HISTORY Pre-Release Preliminary Datasheet Rev. PrD | Page 2 of 24 Preliminary Technical Data AD7150 PRELIMINARY SPECIFICATIONS VDD = 3.0 V to 3.6 V; GND = 0 V; –40°C to +125°C, unless otherwise noted. Table 1. Parameter CAPACITIVE INPUT Capacitive Input Ranges Min IOH Output High Leakage Current POWER REQUIREMENTS VDD-to-GND Voltage IDD Current 3 IDD Current Power-Down Mode 3 Max 4 2 1 0.5 2.0 1.6 1.4 0.8 Resolution Allowed Capacitance to GND Response time Power Supply Rejection Channel-to-Channel Isolation CAPDAC 2 Full Range Resolution AutoDAC Increment / Decrement LOGIC OUTPUTS (OUT1, OUT2) VOL Output Low Voltage VOH Output High Voltage SERIAL INTERFACE LOGIC INPUTS (SCL, SDA) VIH Input High Voltage VIL Input Low Voltage Hysteresis Input Leakage Current (SCL) OPEN-DRAIN OUTPUT (SDA) VOL Output Low Voltage Typ 100 10 TBD TBD 10 160 25 75 0.4 VDD – 0.6 2.1 0.1 3.0 90 1 Test Conditions/Comments pF1 pF pF pF fF1 fF fF fF pF ms fF/V dB 4 pF Range 2 pF Range 1 pF Range 0.5 pF Range pF fF % of CIN Range V V ISINK = 8 mA ISOURCE = 8 mA ±1 V V mV µA 0.4 V ISINK = −6.0 mA 1 µA VOUT = VDD 3.6 100 180 TBD TBD V µA µA µA uA VDD = 3.3 V, nominal –40°C to +85°C –40°C to +125°C –40°C to +85°C –40°C to +125°C 0.8 150 ±0.1 Unit 1 Capacitance units: 1 pF = 10-12 F; 1 fF = 10-15 F. The CAPDAC can be used to shift (offset) the input range. The total capacitance of the sensor can be therefore up to sum of the max CAPDAC value and the input range. With the auto CAPDAC feature, the CAPDAC is adjusted automatically when the CDC input value is lower than 25% or higher than 75% of the CDC input range. 3 Digital inputs equal to VDD or GND 2 Rev. PrD| Page 3 of 24 Preliminary Technical Data AD7150 TIMING SPECIFICATIONS VDD = 3.0 V to 3.6 V; GND = 0 V; Input Logic 0 = 0 V; Input Logic 1 = VDD; –40°C to +125°C, unless otherwise noted. Table 2. Parameter SERIAL INTERFACE1, 2 SCL Frequency SCL High Pulse Width, tHIGH SCL Low Pulse Width, tLOW SCL, SDA Rise Time, tR SCL, SDA Fall Time, tF Hold Time (Start Condition), tHD;STA Set-Up Time (Start Condition), tSU;STA Data Set-Up Time, tSU;DAT Set-Up Time (Stop Condition), tSU;STO Data Hold Time, tHD;DAT (Master) Bus-Free Time (Between Stop and Start Condition, tBUF) 2 0 0.6 1.3 Typ Max Unit 400 kHz µs µs µs µs µs µs µs µs µs µs 0.3 0.3 0.6 0.6 0.1 0.6 0 1.3 Test Conditions/Comments See Figure 2 After this period, the first clock is generated Relevant for repeated start condition Sample tested during initial release to ensure compliance. All input signals are specified with input rise/fall times = 3 ns, measured between the 10% and 90% points. Timing reference points at 50% for inputs and outputs. Output load = 10 pF. tLOW tR tF tHD:STA SCL tHD:STA tHD:DAT tHIGH tSU:STA tSU:DAT tSU:STO SDA tBUF P S S Figure 2. Serial Interface Timing Diagram Rev. PrD | Page 4 of 24 P 05468-003 1 Min Preliminary Technical Data AD7150 ABSOLUTE MAXIMUM RATINGS TA = 25°C, unless otherwise noted. Table 3. Parameter Positive Supply Voltage VDD to GND Voltage on any Input or Output to GND ESD Rating (ESD Association Human Body Model, S5.1) Operating Temperature Range Storage Temperature Range Junction Temperature uSOIC Package θJA, (Thermal Impedance-to-Air) uSOIC Package θJC, (Thermal Impedance-to-Case) Lead Temperature, Soldering (10 sec) IR Reflow, Peak Temperature Rating −0.3 V to + 3.9 V –0.3 V to VDD + 0.3 V TBD V –40°C to +125°C –65°C to +150°C 150°C 206°C/W Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. 44 °C/W 300°C 220°C ESD CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. Rev. PrD| Page 5 of 24 Preliminary Technical Data AD7150 PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS GND 1 10 SDA VDD 2 AD7150 9 SCL CIN2 3 8 OUT2 CIN1 4 TOP VIEW (Not to Scale) 7 OUT1 EXC2 5 6 EXC1 Figure 3. AD7150 Pin Configuration(10-Lead MSOP) Table 4. Pin Function Descriptions Pin No. 1 2 Mnemonic GND VDD Description Ground Pin. Power Supply Voltage. This pin should be decoupled to GND, using a low impedance capacitor, for example 0.1 µF X7R multilayer ceramic. CDC Capacitive Input Channel 2. The measured capacitance (sensor) is connected between the EXC2 pin and CIN2 pin. If not used, this pin can be left open circuit or connected to GND. CDC Capacitive Input Channel 1. The measured capacitance (sensor) is connected between the EXC1 pin and CIN1 pin. If not used, this pin can be left open circuit or connected to GND. CDC Excitation Output. The measured capacitance is connected between the EXC2 pin and CIN2 pin. If not used, this pin should be left as an open circuit. CDC Excitation Output. The measured capacitance is connected between the EXC1 pin and CIN1 pin. If not used, this pin should be left as an open circuit. 3 CIN2 4 CIN1 5 EXC2 6 EXC1 7 8 9 OUT1 OUT2 SCL Logic output. High level on this output indicates proximity detected on capacitive input 1. Logic output. High level on this output indicates proximity detected on capacitive input 2. Serial Interface Clock Input. Connects to the master clock line. Requires a pull-up resistor if not provided elsewhere in the system. 10 SDA Serial Interface Bidirectional Data. Connects to the master data line. Requires a pull-up resistor if not provided elsewhere in the system. Rev. PrD | Page 6 of 24 Preliminary Technical Data AD7150 TYPICAL PERFORMANCE CHARACTERISTICS Figure 4. Figure 7. Figure 5. Figure 8. Figure 6. Figure 9. Rev. PrD| Page 7 of 24 Preliminary Technical Data AD7150 ARCHITECTURE AND MAIN FEATURES +3.3V VDD CSENS1 CIN1 CLOCK GENERATOR PWR DOWN TIMER AD7150 Σ−∆ CDC DIGITAL FILTER SERIAL INTERFACE CAP DAC THRESHOLD SCL EXC1 SDA MUX CSENS2 CIN2 PROGRAMMING INTERFACE OUT1 DIGITAL OUTPUTS EXCITATION EXC2 OUT2 THRESHOLD GND Figure 10. AD7150 Block Diagram OVERVIEW The AD7150 core is a high performance capacitance to digital converter (CDC), which allows the part to be interfaced directly to a capacitive sensor. CAPACITANCE TO DIGITAL CONVERTER (CDC) The comparators compare the CDC result with thresholds, either fixed or dynamically adjusted by the on-chip adaptive threshold algorithm engine. Thus, the outputs indicate a defined change in the input sensor capacitance. CLOCK GENERATOR 0x000 .. 0xFFF DATA CIN Σ -∆ MODULATOR DIGITAL FILTER CSENS 0..4pF The AD7150 also integrates an excitation source and CAPDAC for the capacitive inputs, an input multiplexer, a complete clock generator, a power down timer, control logic, and an I2Ccompatible serial interface for configuring the part and accessing the internal CDC data, status, etc., if required in the system. See Figure 10. EXC EXCITATION Figure 11. CDC Simplified Block Diagram CAPACITANCE TO DIGITAL CONVERTER CAPDAC Figure 11 shows the CDC simplified functional diagram. The converter consists of a second order Σ-Δ (or charge balancing) modulator and a third order digital filter. The measured capacitance CX is connected between an excitation source and the Σ-Δ modulator input. The excitation signal is applied on the CX during the conversion and the modulator continuously samples the charge going through the CX. The digital filter processes the modulator output, which is a stream of 0s and 1s containing the information in 0 and 1 density. The data are processed by the adaptive threshold engine and output comparators; the data can be also read through the serial interface. The AD7150 CDC core maximum full-scale input range is 4 pF. However, the part can accept a higher capacitance on the input and the offset (not-changing component) capacitance up to 10 pF can be balanced by a programmable on-chip CAPDAC. The AD7150 is designed for floating capacitive sensors. Therefore, both CX plates have to be isolated from ground or any other fixed potential node in the system. The AD7150 features slew rate limiting on the excitation voltage output, which decrease the energy of higher harmonics on the excitation signal and dramatically improves the system EMC radiation performance. CAPDAC 10pF CIN(+) 0..4pF CDC 0x000 .. 0xFFF DATA CSENS 10..14pF EXC Figure 12. Using CAPDAC The CAPDAC can be understood as a negative capacitance connected internally to the CIN pin. The CAPDAC has a 6-bit resolution and a monotonic transfer function. The example in Figure 12 shows how to use the CAPDAC to shift the CDC 4 pF input range to measure capacitance between 10 pF to 14 pF. Rev. PrD | Page 8 of 24 Preliminary Technical Data AD7150 COMPARATOR AND THRESHOLD MODES ADAPTIVE THRESHOLD The AD7150 comparators and their thresholds can be programmed to operate in several different modes. In an adaptive mode, the threshold is dynamically adjusted and the comparator output will indicate fast changes and ignore slow changes in the input (sensor) capacitance Alternatively, the threshold can be programmed a constant (fixed) value and the output will indicate all changes in the input capacitance. In an adaptive mode, the threshold(s) are dynamically adjusted, ensuring indication of fast changes (for example an object moving close to a capacitive proximity sensor) and eliminating slow changes in the sensor capacitance (usually caused by environment changes – e.g. humidity or temperature - or changes in the sensor dielectric material over time.). See Figure 17. The AD7150 logic output (active high) indicates either positive or negative change in the input capacitance, in both adaptive and fixed threshold modes; see Figure 13 and Figure 14. FAST CHANGE SLOW CHANGE INPUT CAP. THRESHOLD POSITIVE CHANGE OUTPUT ACTIVE POSITIVE THRESHOLD OUTPUT TIME INPUT CAP. Figure 17. Adaptive Threshold Indicates fast changes and eliminates slow changes in input capacitance OUTPUT ACTIVE OUTPUT DATA AVERAGE TIME Figure 13. Positive Threshold Mode Indicates positive change in input capacitance The adaptive threshold algorithm is based on an average calculated from previous CDC output data. The response of the average to an input capacitance step change (more exactly, response to the change in the CDC output data) is an exponential settling curve, which can be characterized by equation: NEGATIVE CHANGE INPUT CAP. NEGATIVE THRESHOLD OUTPUT ACTIVE Average( N ) = Average(0) + Change(1 − e N / TimeConst ) OUTPUT TIME Figure 14. Negative Threshold Mode Indicates negative change in input capacitance Additionally, for the adaptive mode only, the comparators can work as “window” comparators, indicating input either inside or outside selected sensitivity band; see Figure 15 and Figure 16. POSITIVE THRESHOLD Where Average(N) is the value of average N complete CDC conversion cycles after a step change on the input, Average(0) is the value before the step change, and the TimeConstant can be selected in range between 2 and 65536 in steps of power of 2 by programming the ThrSettling bits in the setup registers. See Figure 18. See Register Descriptions. INPUT CAPACITANCE (CDC DATA) CHANGE INPUT INSIDE THRESHOLD WINDOW INPUT CAP. DATA AVERAGE RESPONSE NEGATIVE THRESHOLD TIME OUTPUT ACTIVE Figure 18 .Data Average Response to Data Step Change OUTPUT TIME Figure 15. In-Window (Adaptive) Threshold Mode POSITIVE THRESHOLD INPUT OUTSIDE THRESHOLD WINDOW INPUT CAP. NEGATIVE THRESHOLD OUTPUT ACTIVE OUTPUT TIME Figure 16. Out-Window (Adaptive) Threshold Mode Rev. PrD| Page 9 of 24 Preliminary Technical Data AD7150 SENSITIVITY DATA AVERAGE + SENSITIVITY In adaptive threshold mode, the output comparator threshold is set as a defined distance (“sensitivity”) above the data average, below the data average, or both, depending on the selected threshold mode of operation – see Figure 19. The sensitivity value is programmable in range of 0 to 255 LSBs of the 12-bit CDC converter. See Register Descriptions. LARGE CHANGE IN DATA DATA AVERAGE DATA AVERAGE – SENSITIVITY TIMEOUT TIME Figure 21. Threshold Timeout after a Large Change in CDC Data DATA POSITIVE THRESHOLD TIMEOUT APPROACHING SENSITIVITY INPUT CAP. DATA AVERAGE THRESHOLD SENSITIVITY NEGATIVE THRESHOLD LARGE CHANGE OUTPUT ACTIVE OUTPUT ACTIVE TIME OUTPUT Figure 19. Threshold Sensitivity TIME Figure 22. Approaching Timeout in Negative Threshold Mode Shortens False Output Trigger HYSTERESIS In adaptive threshold mode, the comparator features hysteresis. The hysteresis is fixed to ¼ of the threshold sensitivity and can be programmable ON or OFF. The comparator does not have any hysteresis in the fixed threshold mode. LARGE CHANGE TIMEOUT RECEDING INPUT CAP. DATA THRESHOLD POSITIVE THRESHOLD OUTPUT ACTIVE HYSTERSIS OUTPUT TIME DATA AVERAGE Figure 23. Positive Timeout in Negative Threshold Mode Shortens Period of Missing Output Trigger OUTPUT ACTIVE OUTPUT AUTO CAPDAC ADJUSTMENT TIME Figure 20. Threshold Hysteresis TIMEOUT In case of a large long change in the capacitive input, when the data average adapting to a new condition might take too long, a timeout can be set. The timeout becomes active (counting) when the CDC data goes outside the band of data average ± sensitivity. When the timeout elapses (a defined number of CDC conversions is counted), the data average, and thus the thresholds, are forced to follow the new CDC data value immediately. See Figure 21. The timeout can be set independently for “approaching” – for change in data towards the threshold, and for “receding” – for change in data away from the threshold. See Figure 22 and Figure 23. See Register Descriptions. In adaptive threshold mode, the part can dynamically adjust the CAPDAC to keep the CDC in an optimal operating capacitive range. When the AutoDAC function is enabled, the CAPDAC value is automatically incremented when the data average exceeds ¾ of the CDC full range, and the CAPDAC value is decremented when the data average goes below ¼ or the CDC full range. The AutoDAC increment or decrement step depends on the selected CDC capacitive input range. See Register Descriptions. POWER DOWN TIMER In power sensitive applications, the AD7150 can be set to automatically enter power down mode after a programmed period of time, in which the outputs have not been activated. The AD7150 can be then returned to a normal operational mode either via the serial interface or by power supply off – on sequence. Rev. PrD | Page 10 of 24 Preliminary Technical Data AD7150 REGISTER DESCRIPTIONS Table 5. Register Summary Pointer Register (Dec) (Hex) Bit 7 Bit 6 Bit 5 Bit 4 Dir PwrDown DacStep2 Bit 3 Default Value OUT1 DacStep1 OUT2 Bit 2 Bit 1 Bit 0 C1/C2 RDY2 RDY1 0 1 1 Status 0 0x00 R Ch1 Data H 1 0x01 R Channel 1 Data – high byte, 0x00 Ch1 Data L 2 0x02 R Channel 1 Data – low byte, 0x00 Ch2 Data H 3 0x03 R Channel 2 Data – high byte, 0x00 Ch2 Data L 4 0x04 R Channel 2 Data – low byte, 0x00 Ch1 Average H 5 0x05 R Channel 1 Average – high byte, 0x00 Ch1 Average L 6 0x06 R Channel 1 Average – low byte, 0x00 Ch2 Average H 7 0x07 R Channel 2 Average – high byte, 0x00 Ch2 Average L 8 0x08 R Channel 2 Average – low byte, 0x00 Ch1 Sens / Thr H 9 0x09 R/W Channel 1 Sensitivity (adaptive) / Threshold – high byte (fixed), 0x08 Ch1Tout / Thr L 10 0x0A R/W Channel 1 Timeout (adaptive) / Threshold – low byte (fixed), 0x86 Ch1 Setup 11 0x0B R/W Ch2 Sens / Thr H 12 0x0C R/W Channel 2 Sensitivity (adaptive) / Threshold (fixed) – high byte, 0x08 Ch2 Tout / Thr L 13 0x0D R/W Channel 2 Timeout (adaptive) / Threshold (fixed) – low byte, 0x86 Ch2 Setup 14 0x0E R/W Configuration 15 0x0F R/W Power Down Timer 16 0x10 R/W Ch1 CAPDAC 17 0x11 R/W Ch2 CAPDAC 18 0x12 R/W Serial Number 3 19 0x13 R Serial Number – byte 3 (MSB) Serial Number 2 20 0x14 R Serial Number – byte 2 Serial Number 1 21 0x15 R Serial Number – byte 1 Serial Number 0 22 0x16 R Serial Number – byte 0 (LSB) Chip ID 23 0x17 R Chip Identification Code 0 1 0 1 0 RngH1 RngL1 - Hyst1 ThrSettling1 – 4-Bit Value 0 0 0 0 0x0B RngH2 RngL2 - 0 ThrFixed 0 – 0 DacEn1 0 DacEn2 0 0 ThrMD1 0 – 0 DacAuto1 0 DacAuto2 0 0 ThrMD0 0 Hyst2 ThrSettling2 – 4-Bit Value 0 0x0B EnCh1 EnCh2 MD2 MD1 1 1 0 0 Power Down Timeout – 6-Bit Value 0x00 Channel 1 CAPDAC – 6-Bit Value 0x00 Channel 2 CAPDAC – 6-Bit Value 0x00 Rev. PrD| Page 11 of 24 MD0 1 Preliminary Technical Data AD7150 STATUS REGISTER Address Pointer 0x00 8 Bits, Read Only, Default Value 0x53 This register indicates the status of the part. The register can be read via the 2-wire serial interface to query status of the outputs, check the CDC finished conversion and whether the CAPDAC has been changed by the auto CAPDAC function. Table 6. Status Register Bit Map Bit Mnemonic Default Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 PwrDown DacStep2 OUT2 DacStep1 OUT1 C1/C2 RDY2 RDY1 0 1 0 1 0 0 1 1 Table 7. Bit 7 6 Mnemonic PwrDown DacStep2 5 OUT2 4 DacStep1 3 OUT1 2 C1/C2 1 RDY2 0 RDY1 Description PwrDown = 1 indicates that the part is in a power down mode. DacStep2 = 0 indicates that the CAPDAC Ch2 was changed after the last CDC conversion as part of the AutoDac function The bit value is updated after each finished CDC conversion on this channel. OUT2 = 1 indicates that the Ch2 data (CIN2 capacitance) crossed the threshold, according to the selected comparator mode of operation. The bit value is updated after each finished CDC conversion on this channel. DacStep1 = 0 indicates that the CAPDAC Ch2 was changed during the last conversion as part of the AutoDac function The bit value is updated after each finished CDC conversion on this channel. OUT1 = 1 indicates that the Ch1 data (CIN1 capacitance) crossed the threshold, according to the selected comparator mode of operation. The bit value is updated after each finished CDC conversion on this channel. The C1/C2 = 0 indicates the last finished CDC conversion was on channel 1, The C1/C2 = 1 indicates the last finished CDC conversion was on channel 2 RDY2 = 0 indicates finished CDC conversion on Ch2. The bit is reset back to 1 when the Ch2 data register is read via serial interface or after the part reset or power-up. RDY1= 0 indicates finished CDC conversion on Ch1. The bit is reset back to 1 when the Ch1 data register is read via serial interface or after the part reset or power-up. DATA REGISTERS AVERAGE REGISTERS Ch1 Address Pointer 0x01, 0x02 Ch2 Address Pointer 0x03,0x04 16 Bits, Read-Only, Default Value 0x0000 Ch1 Address Pointer 0x05, 0x06 Ch2 Address Pointer 0x07,0x08 16 Bits, Read-Only, Default Value 0x0000 CDC output data. The AD7150 has a 12-bit converter, the 12bit result is mapped to the 12 MSB (most significant bits) of the 16-bit data register and the 4 LSB (least significant bits) are always 0. Average calculated from the previous CDC data. The 12-bit CDC result corresponds to the 12 MSB of the average register. The register is updated after a finished conversion on the capacitive channel, with one exception: When the serial interface read operation from the data register is in progress, the data register is not updated and the new capacitance conversion result is lost. The stop condition on the serial interface is considered to be the end of the read operation. Therefore, to prevent incorrect data reading through the serial interface, the two bytes of the data register should be read sequentially using the register address pointer auto-increment feature of the serial interface. The settling time of the average can be set by programming the ThrSettling bits in the setup register. The average register is overwritten directly with the CDC output data, i.e., the history is forgotten, if the timeout is enabled and elapses. FIXED THRESHOLD REGISTERS Ch1 Address Pointer 0x09, 0x0A Ch2 Address Pointer 0x0C,0x0D 16 Bits, Read/Write, Factory Preset 0x0886 Set a constant threshold for the output comparator in the fixed threshold mode. The 12-bit CDC result corresponds to the 12 MSB of the threshold register. The threshold registers are not accessible in the adaptive threshold mode. Rev. PrD | Page 12 of 24 Preliminary Technical Data AD7150 SENSITIVITY REGISTERS Ch1 Address Pointer 0x09 Ch2 Address Pointer 0x0C 8 Bits, Read/Write, Factory Preset 0x08 Sensitivity register sets the distance of the positive threshold above the data average, and the distance of the negative threshold below the data average, in the adaptive threshold mode. DATA POSITIVE THRESHOLD The receding timeout starts when the CDC data cross the data average±sensitivity band in direction away from the threshold, according to the selected positive or negative threshold mode. The receding timeout is not used in the window threshold modes. The receding timeout elapses after 2TimeOutRec conversion cycles. When either approaching or receding timeout elapses (i.e., after the defined number of CDC conversions is counted), the data average, and thus the thresholds, are forced to follow the new CDC data value immediately. Timeout register = 0 disables both timeouts SENSITIVITY DATA AVERAGE SENSITIVITY NEGATIVE THRESHOLD DATA AVERAGE + SENSITIVITY OUTPUT ACTIVE LARGE CHANGE IN DATA TOWARDS THRESHOLD DATA AVERAGE THRESHOLD TIME Figure 24. Threshold Sensitivity The sensitivity is an 8-bit value and is mapped to the lower 8 bits of the 12-bit CDC data, i.e., corresponds to the 16-bit data register as shown in Figure 39. SENSITIVITY TIMEOUT APPROACHING Figure 26. Threshold Timeout Approaching after a Large Change in CDC Data towards Threshold Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 DATA H TIME TIMEOUT RECEDING DATA L Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 DATA AVERAGE + SENSITIVITY 12-BIT CDC RESULT DATA AVERAGE Figure 25. Threshold Timeout after a Large Negative Change in CDC Data THRESHOLD LARGE CHANGE IN DATA AWAY FROM THRESHOLD TIMEOUT REGISTERS Figure 27. Threshold Timeout Receding after a Large Change in CDC Data away from Threshold Ch1 Address Pointer 0x0A Ch2 Address Pointer 0x0D 8 Bits, Read/Write, Factory Preset 0x86 Table 8. Timeout Register Bit Map Bit Mnemonic Default Bit 7-4 TimeOutApr 0x08 TIME Bit 3-0 TimeOutRec 0x06 The registers set timeouts for the adaptive threshold mode. The approaching timeout starts when the CDC data cross the data average±sensitivity band in direction towards the threshold, according to the selected positive, negative or window threshold mode. The approaching timeout elapses after 2TimeOutApr conversion cycles. Rev. PrD| Page 13 of 24 Preliminary Technical Data AD7150 SETUP REGISTERS Ch1 Address Pointer 0x0B Ch2 Address Pointer 0x0E 8 Bits, Read/Write, Factory Preset 0x0B Table 9. Setup Register Bit Map Bit Bit 7 Bit 6 Mnemonic RngH 0 Default Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 RngL - Hyst ThrSettling1 – 4-Bit Value 0 0 0 0x0B Bit 0 Table 10. Bit 7 6 Mnemonic RngH RngL Description Range bits set the CDC input range. Also determine step for AutoDAC function RngH RngL 0 0 1 1 0 1 0 1 Cin Range (pF) 2 0.5 1 4 AutoDAC Step (CAPDAC LSB) 4 1 2 8 5 4 Hyst This bit must be 0 for proper operation. Hyst = 1 disables hysteresis in adaptive threshold mode. Bit has no effect in fixed threshold mode - hysteresis is always disabled in the fixed threshold mode. 3 2 1 0 ThrSettling Determines the settling time constant of the data average, and thus the settling time of the adaptive thresholds. The response of the average to an input capacitance step change (more exact, response to the change in the CDC output data) is an exponential settling curve, characterized by equation: Average( N ) = Average(0) + Change(1 − e N / TimeConst ) Where Average(N) is the value of average after N complete CDC conversion cycles after a step change on the input, Average(0) is the value before the step change, and the TimeConstant can be selected in range between 2 and 65536 conversion cycle multiples, in steps of power of 2, by programming the ThrSettling bits: TimeConst = 2 ( ThrSettling +1) INPUT CAPACITANCE (CDC DATA) CHANGE DATA AVERAGE RESPONSE TIME Figure 28 .Data Average Response to Data Step Change Rev. PrD | Page 14 of 24 Preliminary Technical Data AD7150 CONFIGURATION REGISTER Address Pointer 0x0F 8 Bits, Read/Write, Factory Preset 0x19 Table 11. Configuration Register Bit Map Bit Mnemonic Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 ThrFixed ThrMD1 ThrMD0 EnCh1 EnCh2 MD2 MD1 MD0 0 0 0 1 1 0 0 1 Default Table 12. Bit 7 Mnemonic ThrFixed 6 5 ThrMD1 ThrMD0 4 3 2 1 0 EnCh1 EnCh2 MD2 MD1 MD0 Description ThrFixed = 1 sets the fixed threshold mode. The outputs reflect comparison of data and a fixed (constant) value of the threshold registers. ThrFixed = 0 sets the adaptive threshold mode. The outputs reflect comparison of data to the adaptive thresholds, which is set dynamically based on the previous data and according to the other settings. These bits set the output comparators mode. OUTPUT ACTIVE WHEN ThrMD1 0 0 1 ThrMD0 0 1 0 Threshold Mode Negative Positive In-Window 1 1 Out-Window Adaptive Threshold Mode data < average – sensitivity data > average + sensitivity data > average – sensitivity AND data < average + sensitivity data < average – sensitivity OR data > average + sensitivity Fixed Threshold Mode Data < Threshold Data > Threshold - - Enables conversion on channel 1 Enables conversion on channel 2 Converter mode of operation setup. MD2 0 0 MD1 0 0 MD0 0 1 Mode Idle Cont. conversion 0 1 0 Single conversion 0 1 1 Power-Down 1 X X Reserved Description Part is fully powered up, but performing no conversion Part is repeatedly performing conversions on the enabled channel(s). If two channels are enabled, part is sequentially switching between them. Part performs a single conversion on the enabled channel. If two channels are enabled, the part will perform two conversions, one on each channel. After finishing the conversion(s), the part goes to the idle mode. Powers down the on-chip circuits, except the digital interface. Do not use these modes. Rev. PrD| Page 15 of 24 Preliminary Technical Data AD7150 POWER DOWN TIMER REGISTER Address Pointer 0x10 8 Bits, Read/Write, Factory Preset 0x00 Table 13. Setup Register Bit Map Bit Mnemonic Default Bit 7 – Bit 6 – 0 0 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Power Down Timeout – 6-Bit Value Bit 0 0xPP Table 14. Bit 7-6 5-0 Mnemonic Power Down Timeout Description These bits must be 0 for proper operation Defines period duration of the power down timeout. If the output comparator outputs have not been activated during the programmed period, the part enters automatically power down mode. The part can be then returned to a normal operational mode either via the serial interface or by power supply off – on sequence. The period is programmable in steps of 4 hours. For example, setting value to 0x06 sets the duration to 24 hours, the maximum value of 0x3F corresponds to approximately 10.5 days. Value of 0x00 disables the power down timeout and the part will not enter power down mode automatically. CAP DAC B REGISTERS Ch1 Address Pointer 0x11 Ch2 Address Pointer 0x12 8 Bits, Read/Write, Factory Preset 0x00 Table 15. Setup Register Bit Map Bit Mnemonic Default Bit 7 Bit 6 DacEn DacAuto1 Bit 5 Bit 4 Channel 1 CAPDAC – 6-Bit Value Bit 3 Bit 2 P P 0xPP Bit 1 Bit 0 Table 16. Bit 7 6 Mnemonic DacEn DacAuto Description DacEn = 1 enables capacitive DAC DacAuto = 1 enables the AutoDAC function in the adaptive threshold mode. When the AutoDAC function is enabled, the part dynamically adjust the CAPDAC to keep the CDC in an optimal operating capacitive range. The CAPDAC value is automatically incremented when the data average exceeds ¾ of the CDC full range, and the CAPDAC value is decremented when the data average goes below ¼ or the CDC full range. The AutoDAC increment or decrement step depends on the selected CDC capacitive input range. Bit has no effect in fixed threshold mode - AutoDAC function is always disabled in the fixed threshold mode. 5-0 CAPDAC CAPDAC value, Code 0x00 ≈ 0 pF, Code 0x3F ≈ CAPDAC full range. SERIAL NUMBER REGISTERS CHIP ID REGISTERS Address Pointer 0x13, 0x14, 0x15, 0x16 32 Bits, Read Only, 0xXXXX Address Pointer 0x17 8 Bits, Read Only, 0xXX Register holds a serial number, unique for each individual part. Chip identification code, used in factory manufacturing and test. Rev. PrD | Page 16 of 24 Preliminary Technical Data AD7150 SERIAL INTERFACE The AD7150 supports an I2C-compatible 2-wire serial interface. The two wires on the I2C bus are called SCL (clock) and SDA (data). These two wires carry all addressing, control, and data information one bit at a time over the bus to all connected peripheral devices. The SDA wire carries the data, while the SCL wire synchronizes the sender and receiver during the data transfer. I2C devices are classified as either master or slave devices. A device that initiates a data transfer message is called a master, while a device that responds to this message is called a slave. incrementer allow block data to be written or read from the starting address and subsequent incremental addresses. To control the AD7150 device on the bus, the following protocol must be followed. First, the master initiates a data transfer by establishing a start condition, defined by a high-tolow transition on SDA while SCL remains high. This indicates that the start byte follows. This 8-bit start byte is made up of a 7-bit address plus an R/W bit indicator. The user can also access any unique register (address) on a oneto-one basis without having to update all the registers. The address pointer register contents cannot be read. All peripherals connected to the bus respond to the start condition and shift in the next 8 bits (7-bit address + R/W bit). The bits arrive MSB first. The peripheral that recognizes the transmitted address responds by pulling the data line low during the ninth clock pulse. This is known as the acknowledge bit. All other devices withdraw from the bus at this point and maintain an idle condition. An exception to this is the general call address, which is described later in this document. The idle condition is where the device monitors the SDA and SCL lines waiting for the start condition and the correct address byte. The R/W bit determines the direction of the data transfer. A Logic 0 LSB in the start byte means that the master writes information to the addressed peripheral. In this case the AD7150 becomes a slave receiver. A Logic 1 LSB in the start byte means that the master reads information from the addressed peripheral. In this case, the AD7150 becomes a slave transmitter. In all instances, the AD7150 acts as a standard slave device on the I2C bus. The start byte address for the AD7150 is 0x90 for a write and 0x91 for a read. READ OPERATION When a read is selected in the start byte, the register that is currently addressed by the address pointer is transmitted on to the SDA line by the AD7150. This is then clocked out by the master device and the AD7150 awaits an acknowledge from the master. If an acknowledge is received from the master, the address autoincrementer automatically increments the address pointer register and outputs the next addressed register content on to the SDA line for transmission to the master. If no acknowledge is received, the AD7150 return to the idle state and the address pointer is not incremented. The address pointers’ auto- In continuous conversion mode, the address pointers’ autoincrementer should be used for reading a conversion result. That means, the three data bytes should be read using one multibyte read transaction rather than three separate single byte transactions. The single byte data read transaction may result in the data bytes from two different results being mixed. The same applies for six data bytes if both the capacitive and the voltage/temperature channel are enabled. If an incorrect address pointer location is accessed or, if the user allows the auto-incrementer to exceed the required register address, the following applies: • In read mode, the AD7150 continues to output various internal register contents until the master device issues a no acknowledge, start, or stop condition. The address pointers’ auto-incrementer’s contents are reset to point to the status register at address 0x00 when a stop condition is received at the end of a read operation. This allows the status register to be read (polled) continually without having to constantly write to the address pointer. • In write mode, the data for the invalid address is not loaded into the AD7150 registers but an acknowledge is issued by the AD7150. WRITE OPERATION When a write is selected, the byte following the start byte is always the register address pointer (subaddress) byte, which points to one of the internal registers on the AD7150. The address pointer byte is automatically loaded into the address pointer register and acknowledged by the AD7150. After the address pointer byte acknowledge, a stop condition, a repeated start condition, or another data byte can follow from the master. A stop condition is defined by a low-to-high transition on SDA while SCL remains high. If a stop condition is ever encountered by the AD7150, it returns to its idle condition and the address pointer is reset to address 0x00. If a data byte is transmitted after the register address pointer byte, the AD7150 load this byte into the register that is currently addressed by the address pointer register, send an acknowledge, and the address pointer auto-incrementer automatically increments the address pointer register to the next internal register address. Thus, subsequent transmitted data bytes are loaded into sequentially incremented addresses. Rev. PrD| Page 17 of 24 Preliminary Technical Data AD7150 If a repeated start condition is encountered after the address pointer byte, all peripherals connected to the bus respond exactly as outlined above for a start condition, that is, a repeated start condition is treated the same as a start condition. When a master device issues a stop condition, it relinquishes control of the bus, allowing another master device to take control of the bus. Hence, a master wanting to retain control of the bus issues successive start conditions known as repeated start conditions. GENERAL CALL When a master issues a slave address consisting of seven 0s with the eighth bit (R/W bit) set to 0, this is known as the general call address. The general call address is for addressing every device connected to the I2C bus. The AD7150 acknowledge this address and read in the following data byte. If the second byte is 0x06, the AD7150 are reset, completely uploading all default values. The AD7150 do not respond to the I2C bus commands (do not acknowledge) during the default values upload for approximately TBD µs. AD7150 RESET To reset the AD7150 without having to reset the entire I2C bus, an explicit reset command is provided. This uses a particular address pointer word as a command word to reset the part and upload all default settings. The AD7150 do not respond to the I2C bus commands (do not acknowledge) during the default values upload for approximately TBD µs. The AD7150 do not acknowledge any other general call commands. The reset command address word is 0xBF. SCLOCK S 1–7 8 9 1–7 8 9 START ADDR R/W ACK SUBADDRESS ACK 1–7 DATA 8 9 P ACK STOP 05468-006 SDATA Figure 29. Bus Data Transfer S SLAVE ADDR A(S) SUB ADDR A(S) DATA S SLAVE ADDR A(S) S = START BIT P = STOP BIT DATA A(S) P LSB = 1 LSB = 0 READ SEQUENCE A(S) SUB ADDR A(S) S SLAVE ADDR A(S) = ACKNOWLEDGE BY SLAVE A(M) = ACKNOWLEDGE BY MASTER A(S) DATA A(M) A(S) = NO-ACKNOWLEDGE BY SLAVE A(M) = NO-ACKNOWLEDGE BY MASTER Figure 30. Write and Read Sequences Rev. PrD | Page 18 of 24 DATA A(M) P 05468-007 WRITE SEQUENCE Preliminary Technical Data AD7150 HARDWARE DESIGN CONSIDERATIONS OVERVIEW PARASITIC RESISTANCE TO GROUND The AD7150 is an interface to capacitive sensors. On the output side, the AD7150 can work as a standalone device, using the power-up default register settings and flagging the result on digital outputs. Alternatively, the AD7150 can be interfaced to a microcontroller via the 2-wire serial interface, offering flexibility by overwriting the AD7150 register values from the host with a user specific setup. PARASITIC CAPACITANCE TO GROUND CIN CDC RGND2 DATA EXC Figure 32. Parasitic Resistance to Ground The AD7150 CDC result would be affected by a leakage current from the CX to ground, therefore the CX should be isolated from the ground. (The equivalent resistance between the CX and ground should be maximized – see Figure 32). The limit will be specified after the AD7150 characterization. PARASITIC PARALLEL RESISTANCE DATA CIN 05468-012 CX EXC CDC CX CX CGND2 CIN CDC DATA RP EXC 05468-022 CGND1 RGND1 05468-013 On the input side, the sensor (CX) can be connected directly between the AD7150 EXC and the CIN pins. The way how is it connected and the electrical parameters of the sensor connection, such as parasitic resistance or capacitance, can affect the system performance. Therefore, any circuit with additional components in the capacitive front end, such as overvoltage protection, has to be carefully designed considering the AD7150 specified limits and information provided in this section. Figure 31. Parasitic Capacitance to Ground The CDC architecture used in the AD7150 measures the capacitance CX connected between the EXC pin and the CIN pin. In theory, any capacitance CGND to ground should not affect the CDC result (see Figure 31). Figure 33. Parasitic Parallel Resistance The practical implementation of the circuitry in the chip implies certain limits and the result is gradually affected by capacitance to ground. See the allowed capacitance to GND in the specification table for CIN and excitation. The AD7150 CDC measures the charge transfer between EXC pin and CIN pin. Any resistance connected in parallel to the measured capacitance CX (see Figure 33), 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. The equivalent parallel capacitance (or error caused by the parallel resistance) can be approximately calculated as Further details will be specified after the AD7150 characterization. CP = 1 RP × FEXC × 4 Where RP is the parallel resistance and FEXC is the excitation frequency. Further details will be specified after the AD7150 characterization. Rev. PrD | Page 19 of 24 Preliminary Technical Data AD7150 PARASITIC SERIAL RESISTANCE INPUT EMC PROTECTION 39kΩ CX RS1 CIN CIN 82kΩ 68pF 22pF CDC DATA CDC EXC 10kΩ 47pF GND CX 05468-023 Figure 36. AD7150 CIN EMC Protection RS2 EXC Figure 34. Parasitic Serial Resistance Some applications may have specific requirements for EMC protection. Figure 36 shows one of the possible input circuit configurations improving the system EMC robustness. The AD7150 CDC result is affected by a resistance in series with the measured capacitance. The total serial resistance, which refers to RS1 + RS2 on Figure 34, should be in order of hundreds Ω. Further details will be specified after the AD7150 characterization. INPUT OVERVOLTAGE PROTECTION CDC RS1 CIN RS2 EXC2 CX GND Figure 35. AD7150 CIN Overvoltage Protection The AD7150 capacitive input has an internal ESD protection. However, some applications may require an additional overvoltage protection depending on the application specific requirements. Any additional circuit in the capacitive front end has to be carefully designed, especially with respect to the limits recommended for max. capacitance to ground, max. serial resistance, max. leakage, etc. Further details will be specified after the AD7150 characterization. Rev. PrD | Page 20 of 24 Preliminary Technical Data AD7150 APPLICATION EXAMPLES VDD CIN1 SDA AD7150 CSENS1 EXC1 LED1 SCL LED2 OUT1 3.6V BATTERY CIN2 CSENS2 OUT2 EXC2 GND Figure 37. AD7150 Standalone Operation Application Diagram +3.3V VDD CIN1 AD7150 CSENS1 SDA SDA SCL SCL OUT1 IRQ1 OUT2 IRQ2 HOST uC EXC1 CIN2 CSENS2 EXC2 GND Figure 38. AD7150 Interfaced to a Host Microcontroller Rev. PrD | Page 21 of 24 Preliminary Technical Data AD7150 Notes Rev. PrD | Page 22 of 24 Preliminary Technical Data AD7150 Notes Rev. PrD | Page 23 of 24 Preliminary Technical Data AD7150 3.00 BSC 10 6 4.90 BSC 3.00 BSC 1 5 PIN 1 0.50 BSC 0.95 0.85 0.75 0.15 0.00 1.10 MAX 0.27 0.17 SEATING PLANE 0.23 0.08 8° 0° 0.80 0.60 0.40 COPLANARITY 0.10 COMPLIANT TO JEDEC STANDARDS MO-187BA Figure 39. 10-Lead Mini Small Outline Package [MSOP] (RM-10) Dimensions shown in millimeters Purchase of licensed I2C components of Analog Devices or one of its sublicensed 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. © 2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. PR06517-0-11/06(PrD) Rev. PrD | Page 24 of 24