AS1716 D a ta s h e e t C a pa c i t i v e S e n s o r I n t e r f a c e 1 General Description 2 Key Features AS1716 is an analog front end specifically designed for unbiased Capacitive Sensors, as for instance Knock Sensors in Automotive, to be interfaced with Analog Digital Converters with Sample and Hold input stages. ! Differential input stage with wide input range ! Resistive sensor biasing (VDDA/2) ! Programmable Gain (x0.5, x1, x2, x4) The device provides differential inputs, a 1st order low pass filter to cutoff the high frequency noise components, differential to single ended conversion, programmable gain stage and a 2 pole low pass Multiple Feedback Filter. ! Internal 2 order low pass Multiple Feedback Filter with a min. cut off frequency of 16kHz ! Single supply operation: 4.5V to 5.5V ! Operating Temperature range: -40°C to +125°C ! High CMRR: 55dB (min) ! EMC characterized by IEC 61967-4 (1Ω / 150Ω Method) ! EMC characterized by IEC 62132-4 (Direct Power Injection) ! Automotive qualified to AECQ100 for IC and PPAP level 3 ! 8-pin SOIC Package The Knock Sensor is a Piezo Electric device that generates a voltage if it is stressed. It senses knock and transmits information to the electronic engine management control unit. This influences process control in the engine, for example timing and fuel injection until knock is eliminated. The capacitive sensor is biased via resistors to a voltage level of VDDA/2. nd 3 Applications Analog front end for Capacitive Sensors to Analog to Digital Converters and DSP. Figure 1. AS1716 Block Diagram VDDA VSSA NC - INN + VDDA VDDA/2 Gain Control x0.5, x1, x2, x4 + - + + - OUT VDDA/2 VDDA/2 Multiple Feedback LP Filter fc ~23kHz typ. - INP VDDA/2 + AS1716 VDDA/2 GA www.austriamicrosystems.com GB Revision 1.00 1 - 12 AS1716 Datasheet - P i n o u t 4 Pinout Pin Assignment Figure 2. Pin Assignments (Top View) VDDA 1 GA 8 OUT 7 VSSA 2 AS1716 GB 3 6 NC INP 4 5 INN Pin Description Table 1. Pin Description Pin Name Pin Number VDDA 1 Positive Supply. GA 2 Gain selection. Internal pull-down of 100kΩ GB 3 Gain selection. Internal pull-down of 100kΩ INP 4 Non-Inverting Input. INN 5 Inverting Input. NC 6 Not Connected. Must be left unconnected in the application VSSA 7 Negative Supply. OUT 8 Signal Output. www.austriamicrosystems.com Description Revision 1.00 2 - 12 AS1716 Datasheet - A b s o l u t e M a x i m u m R a t i n g s 5 Absolute Maximum Ratings Stresses beyond those listed in Table 2 may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in Electrical Characteristics on page 4 is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Table 2. Absolute Maximum Ratings Parameter Min VDDA, VSSA GA, GB, OUT, INP, INN, NC Max Units + 7.0 V V To get an overvoltage protection of up to +16V at the system level, apply external resistors (typ. 1kΩ) on the pins INP and INN. ±4 kV AEC-Q100-002, @ TA = +25ºC AEC-Q100-004, @ TA = +25ºC VSSA - VDDA + 0.3 0.3 ESD Latchup Immunity -100 +100 mA Operating Temperature Range -40 +125 ºC Junction Temperature Storage Temperature Range Package Body Temperature www.austriamicrosystems.com -65 Comments +150 ºC +150 ºC +260 Revision 1.00 ºC The reflow peak soldering temperature (body temperature) specified is in accordance with IPC/JEDEC J-STD020D “Moisture/Reflow Sensitivity Classification for Non-Hermetic Solid State Surface Mount Devices”. The lead finish for Pb-free leaded packages is matte tin (100% Sn). 3 - 12 AS1716 Datasheet - E l e c t r i c a l C h a r a c t e r i s t i c s 6 Electrical Characteristics TA = -40ºC to +125ºC, Parameters are measured at VDDA = 4.5V to 5.5V, RLOAD = 100Ω serial to CLOAD = 10nF, TA = +25ºC and are refering to VSSA, unless otherwise specified. Typical values are listed for reference only and will not be tested. Table 3. Electrical Characteristics Symbol Parameter Condition Min Typ Max Unit DC Electrical Characteristics VDDA Supply Voltage Range @ pin VDDA 4.5 5 5.5 V IDDA Supply Current @ pin VDDA 3 4.5 9 mA 6 dB VDDA V PSRR Power Supply Rejection Ratio VCM Common Mode input Range CMRR Common Mode Rejection Ratio RIN Differential Input Resistance between pins INN and INP VREF Internal Common Mode Input Voltage INP shorted to INN VOFF Offset Voltage Gain1, VINP = VINN @ VCM = VDDA/2, @ pin OUT VIL Logic Low (GA, GB) @ pin GA and GB VIH Logic High (GA, GB) @ pin GA and GB Leakage Current (GA, GB) VDDA = 5V, Gain4 Hysteresis @ pin GA and GB RPD Pull-Down Resistor Gain0.5 1 ILEAK @ pins INN, INP VSSA 55 70 dB 100 VDDA/2 VDDA/2 -2% VREF -10 130 kΩ VDDA/2 +2% V VREF +10 mV 1.2 V 2.0 V 1 µA 100 200 mV @ pin GA and GB 50 100 150 Overall gain 0.5 GA = GB = 1 0.5-10% 0.5 0.5+10% Gain1 Overall gain 1 GA = 1, GB = 0 1-10% 1 1+10% Gain2 Overall gain 2 GA = 0, GB = 1 2-5% 2 2+5% Gain4 Overall gain 4 GA = GB = 0, default setting 4-5% 4 4+5% RL External Serial Resistor 100 1k Ω CL External Capacitive Load RL serial to CL (see Figure 13 on page 9) 0.01 10 nF ISHORT+ Positive Short Circuit Current VOUT is driven to VDDA and VOUT is connected to VSSA 25 mA ISHORT- Negative Short Circuit Current VOUT is driven to VSSA and VOUT is connected to VDDA 25 mA VOUT-L Output Range Low @ pin VOUT VSSA+ 0.05 V VOUT-H Output Range High @ pin VOUT VDDA0.05 V VHYST 1 www.austriamicrosystems.com Revision 1.00 kΩ 4 - 12 AS1716 Datasheet - E l e c t r i c a l C h a r a c t e r i s t i c s Table 3. Electrical Characteristics (Continued) Symbol Parameter Condition Min Typ Max Unit 16 23 29 kHz AC Electrical Characteristics fC Filter Cut-off Frequency VDDA = 4.5V, GA = GB = 0, INP-INN = 1VPP, fIN = 16kHz and 29kHz THD Total Harmonic Distortion VDDA = 5V, fIN = 1kHz, INP-INN = 8VPP, Gain0.5 VNOISE RMS noise at OUT Gain4, fC = 50Hz - 23kHz 80 dB 1 mVRMS 1. Guaranteed by design www.austriamicrosystems.com Revision 1.00 5 - 12 AS1716 Datasheet - Ty p i c a l O p e r a t i n g C h a r a c t e r i s t i c s 7 Typical Operating Characteristics VDDA = 5.0V, TA = +25ºC (unless otherwise specified). Figure 3. CMRR vs. Temperature; GA = GB = 0 Figure 4. Supply Current vs. Temperature; 10 -60 Supply Current (mA) 9 CMRR (dB) -65 -70 -75 8 7 6 5 4 3 2 1 -80 -40 -20 0 20 40 60 80 0 -40 -20 100 120 Temperature (°C) 20 60 80 100 120 Figure 6. THD vs. Frequency -75 20 -76 0 -77 -20 THD (dbV) -78 -79 -80 -81 -82 -40 -60 -80 -100 -83 -120 -84 -85 -40 -20 -140 0 20 40 60 80 100 120 10 100 Temperature (°C) 1000 10000 100000 Frequency (Hz) Figure 7. Transfer Characteristics Figure 8. Phase Gain 10 100 0 -10 0 -20 Phase Gain (deg) Transfer Characteristic (dB) 40 Temperature (°C) Figure 5. THD vs. Temperature THD (dB) 0 -30 -40 -50 -60 -70 -90 -200 -300 min t yp max -80 -100 -100 min t yp max -400 1 10 100 1000 10000 Frequency (kHz) www.austriamicrosystems.com 1 10 100 1000 10000 Frequency (kHz) Revision 1.00 6 - 12 AS1716 Datasheet - D e t a i l e d D e s c r i p t i o n 8 Detailed Description Sensor Biasing and Input Protection Resistors Due to the capacitive and differential nature of the knock sensor, the common mode voltage for the sensor must be set. This is ensured by the first amplifier, whose virtual ground is biasing the sensor via a of 50kΩ resistor. Due to a failure, voltages up to 16V can occur on the input pins. In this case two external serial resistors of 1kΩ must be applied at the inputs. These resistors are limiting the current, when the on chip protection diode opens. Figure 9. Sensor Biasing 560k 1200pF 100pF 1k + INN VDDA VDDA/2 Due to failure up to 16V typical sensor + - VDDA/2 100pF 1k + INP VDDA/2 Inverting Input Structure The Input Strucutre is a first order low-pass filter and fulfills two main functions. First, it is used for biasing the sensor and second, the first order low-pass filter characteristic is used for noise suppression. Figure 10. Input Buffer + VDDA/2 www.austriamicrosystems.com Revision 1.00 7 - 12 AS1716 Datasheet - D e t a i l e d D e s c r i p t i o n Fully Differential to Single Ended Conversion The Subtractor block converts the filtered differential sensor signal into a single ended signal. Further this block provides also the gain setting (see Section Gain Settings). Figure 11. Subtractor Block Gain Control x0.5, x1, x2, x4 + Gain Settings By means of pins GA and GB, 4 gain settings (x0.5, x1, x2, x4) can be realized. The default gain setting is 4, GA=0 and GB=0. Table 4. Gain Settings Gain GA GB 0.5 1 1 1 1 0 2 0 1 4 0 0 Multiple Feedback Filter The Multiple Feedback Filter provides a second order low pass characteristics with a minimum cut-off frequency of 16kHz and a typical fC of 23kHz. The Multiple Feedback configuration is used to avoid aliasing, to filter out high frequency components. The Output is able to drive a resistor from 100Ω to 1kΩ serial to a 10nF capacitor. Figure 12. Multiple Feedback Filter + OUT VDDA/2 Multiple Feedback LP filter fc ~23kHz typ. www.austriamicrosystems.com Revision 1.00 8 - 12 AS1716 Datasheet - A p p l i c a t i o n I n f o r m a t i o n 9 Application Information Figure 13. Application Diagram, minimal requirements 100nF 10µF VDDA VSSA V 4.5...5.5V NC AS1716 100pF 1k + INN VDDA Due to failure up to 16V + - Gain Control x0.5, x1, x2, x4 - + + VDDA/2 typical sensor VDDA/2 Multiple Feedback LP filter fc ~23kHz typ. 1k 100pF - + INP 100Ω to 1k OUT 12 Bit AD 50k S/s 10nF 560k 1200pF VDDA/2 µC VDDA/2 VDDA/2 GA GB Values of the suggested external components are indicative and need to be characterized for each specific application. Typical Piezo Sensor: ! Resistor from 500kΩ to 1MΩ ! Capacity from 900nF to 1.5µF Typical wire equivalent circuit: ! Capacity to groung from 100pF to 400pF / meter ! Capacity between wires strongly depends on type of wires (twisted-pair strongly suggested) ! Resistance is typical 50mΩ / meter @ 20°C Layout rules ! Input Resistors and Capacitors at the inputs should be placed as close as possible to the stonger possible source of disturbances (i.e. the input connector). ! The input lines should be kept as short as possible and routed close to each other. ! The filter capacitor (100nF) on supply should be a ceramic type and placed as close as possible to the chip. ! VSSA and VDDA lines on PCB should have larger width than other signals to minimize resistance, especially if the 10µF capacitor is not very close to the chip. ! The output line should be kept as short as possible. www.austriamicrosystems.com Revision 1.00 9 - 12 AS1716 Datasheet - P a c k a g e D r a w i n g s a n d M a r k i n g s 10 Package Drawings and Markings The device is available in a 8-pin SOIC package. Figure 14. 8-pin SOIC Package Dimensions Notes: 1. Lead coplanarity should be 0 to 0.10mm (.004”) max. 2. Package surface finishing: - Top, matte (charmilles #18-30) - All sides, matte (charmilles +18-30) - Bottom, smooth or matte (charmilles +18-30) 3. All dimensions excluding mold flashes and end flash from the package body shall not exceed 0.25mm (.010”) per side. 4. Details of pin #1 mark are optional but must be located within the area indicated. www.austriamicrosystems.com Revision 1.00 Symbol A A1 A2 B C D E e H h L α ZD Min Max 1.52 1.72 0.10 0.25 1.37 1.57 0.36 0.46 0.19 0.25 4.80 4.98 3.81 3.99 1.27BSC 5.80 6.20 0.25 0.50 0.41 1.27 0º 8º 0.53REF 10 - 12 AS1716 Datasheet - O r d e r i n g I n f o r m a t i o n 11 Ordering Information The device is available as the standard product shown in Table 5. Table 5. Ordering Information Ordering Code Marking Description Delivery Form Package AS1716A-ASOT AS1716A Capacitive Sensor Interface, 16kHz Tape and Reel 8-pin SOIC All devices are RoHS compliant and free of halogene substances. www.austriamicrosystems.com Revision 1.00 11 - 12 AS1716 Datasheet Copyrights Copyright © 1997-2009, austriamicrosystems AG, Schloss Premstaetten, 8141 Unterpremstaetten, Austria-Europe. Trademarks Registered ®. All rights reserved. The material herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. All products and companies mentioned are trademarks or registered trademarks of their respective companies. Disclaimer Devices sold by austriamicrosystems AG are covered by the warranty and patent indemnification provisions appearing in its Term of Sale. austriamicrosystems AG makes no warranty, express, statutory, implied, or by description regarding the information set forth herein or regarding the freedom of the described devices from patent infringement. austriamicrosystems AG reserves the right to change specifications and prices at any time and without notice. Therefore, prior to designing this product into a system, it is necessary to check with austriamicrosystems AG for current information. This product is intended for use in normal commercial applications. Applications requiring extended temperature range, unusual environmental requirements, or high reliability applications, such as military, medical life-support or lifesustaining equipment are specifically not recommended without additional processing by austriamicrosystems AG for each application. For shipments of less than 100 parts the manufacturing flow might show deviations from the standard production flow, such as test flow or test location. The information furnished here by austriamicrosystems AG is believed to be correct and accurate. However, austriamicrosystems AG shall not be liable to recipient or any third party for any damages, including but not limited to personal injury, property damage, loss of profits, loss of use, interruption of business or indirect, special, incidental or consequential damages, of any kind, in connection with or arising out of the furnishing, performance or use of the technical data herein. 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