Datasheet AS1716 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 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 Resistive sensor biasing (VDDA/2) Programmable Gain (x0.5, x1, x2, x4) nd Single supply operation: 4.5V to 5.5V Operating Temperature range: -40°C to +125°C 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. High CMRR: 55dB (min) EMC characterized by IEC 61967-4 (1Ω / 150Ω Method) EMC characterized by IEC 62132-4 (Direct Power Injection) The capacitive sensor is biased via resistors to a voltage level of VDDA/2. Automotive qualified to AECQ100 for IC and PPAP level 3 8-pin SOIC Package 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/Capacitive-Sensors/AS1716 GB Revision 1.02 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 Description 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/Capacitive-Sensors/AS1716 Revision 1.02 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 Max Units +7 V Comments Electrical Parameters VDDA, VSSA GA, GB, OUT, INP, INN, NC Input Current (latch-up immunity) VSSA - VDDA + 0.3 0.3 -100 +100 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. mA Norm: AEC-Q100-004, @ TA = +25ºC kV Norm: AEC-Q100-002, @ TA = +25ºC Electrostatic Discharge Electrostatic Discharge HBM ±4 Temperature Ranges and Storage Conditions Storage Temperature Range -65 Junction Temperature Package Body Temperature Humidity non-condensing 5 Moisture Sensitive Level www.austriamicrosystems.com/Capacitive-Sensors/AS1716 +150 ºC +150 ºC +260 ºC 85 % 3 The reflow peak soldering temperature (body temperature) specified is in accordance with IPC/ JEDEC J-STD-020 “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). Represents a max. floor life time of 168h Revision 1.02 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 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. All limits are guaranteed. The parameters with min and max values are guaranteed with production tests or SQC (Statistical Quality Control) methods. Table 3. Electrical Characteristics Symbol Parameter TAMB Operating Temperature Range Condition Min Typ -45 Max Unit +125 °C 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 1 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 ILEAK Leakage Current (GA, GB) VDDA = 5V, Gain4 Hysteresis @ pin GA and GB RPD Pull-Down Resistor Gain0.5 @ pins INN, INP VSSA 55 dB 70 130 kΩ VDDA/2 - VDDA/2 2% VDDA/2 +2% V - VREF +10 mV 1.2 V VREF 10 100 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 1k Ω External Capacitive Load RL serial to CL (see Figure 13 on page 8) 100 CL 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 kΩ 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 16 23 29 80 kHz dB 1 mVRMS 1. Guaranteed by design www.austriamicrosystems.com/Capacitive-Sensors/AS1716 Revision 1.02 4 - 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 95 9 90 8 Supply Current (mA) 100 CMRR (dB) 85 80 75 70 65 7 6 5 4 3 60 2 55 1 50 -40 -20 0 20 40 60 0 -40 -20 80 100 120 0 Temperature (°C) Figure 5. THD vs. Temperature 20 -76 0 60 80 100 120 -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 Figure 6. THD vs. Frequency -75 -77 THD (dB) 20 Temperature (°C) -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 1 Frequency (kHz) www.austriamicrosystems.com/Capacitive-Sensors/AS1716 10 100 1000 10000 Frequency (kHz) Revision 1.02 5 - 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/Capacitive-Sensors/AS1716 Revision 1.02 6 - 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/Capacitive-Sensors/AS1716 Revision 1.02 7 - 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/Capacitive-Sensors/AS1716 Revision 1.02 8 - 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 Figure 14. 8-pin SOIC Marking Table 5. Packaging Code YYWWMZZ YY last two digits of the current year WW manufacturing week www.austriamicrosystems.com/Capacitive-Sensors/AS1716 Revision 1.02 M ZZ plant identifier free choice / traceability code 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 Figure 15. 8-pin SOIC Package Dimensions www.austriamicrosystems.com/Capacitive-Sensors/AS1716 Revision 1.02 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 6. Table 6. Ordering Information Ordering Code Marking Description Delivery Form Package AS1716-ASOT AS1716 Capacitive Sensor Interface, 16kHz Tape and Reel 8-pin SOIC Note: All products are RoHS compliant. Buy our products or get free samples online at ICdirect: http://www.austriamicrosystems.com/ICdirect For further information and requests, please contact us mailto:[email protected] or find your local distributor at http://www.austriamicrosystems.com/distributor www.austriamicrosystems.com/Capacitive-Sensors/AS1716 Revision 1.02 11 - 12 AS1716 Datasheet Copyrights Copyright © 1997-2011, austriamicrosystems AG, Tobelbaderstrasse 30, 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. 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