SENSOR OVERL. CONVERSION ROGRAM ABLE ACIT RESIST REGIST SERI
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Data Sheet XE2004
SENSOR
OVERL. CONVERSION
ROGRAM ABLE ACIT RESIST REGIST SERIAL ERFACE
XE2004
XE2004
Programmable Low-Power Capacitive Sensor Conditioning
GENERAL DESCRIPTION
XE2004 high precision capacitance-tovoltage converter, based analog signal path with digital programmable gain, offset non-linearity. low-power, low-voltage device, XE2004 provides power-on-reset sensor overload detection. XE2004 available dice SOIC.
PRODUCT FEATURES
high precision capacitance-to-voltage conversion digital programming analog signal path read-out electrically floating capacitances output voltage proportional supply voltage power-on reset sensor overload detection bandwidth resolves down 0.25e-18 F/sqrt(Hz) wide voltage supply range low-power operation: industrial extended temperature operating range
APPLICATIONS
Micro-machined sensors MEMS Single differential capacitive sensors Pressure sensors Touch sensors Flow sensors fluid control humidity sensors Portable, battery operated sensors
DEVICE OPTIONS
SOIC dice temperature range (I-grade) temperature range (E-grade)
Cool Solutions Wireless Connectivity
XEMICS e-mail: info@xemics.com web: www.xemics.com
Data Sheet XE2004
FUNCTIONAL DESCRIPTION
XE2004 implements capacitance-to-voltage conversion. output voltage proportional supply voltage, linearized expression including sensor capacitances supply voltage. ANALOG SIGNAL PATH: XE2004 composed stages. first stage capacitance-to-voltage converter. based floating charge amplifier architecture. This allows operate only with capacitive sensors that have electrically floating electrodes. second stage programmable gain amplifier. DIGITAL CALIBRATION: Offset, span linearity analog output signal digitally adjusted. calibration settings stored on-chip registers. power-on-reset sequence XE2004 allows upload calibration data from external nonvolatile memory host control equipment into registers. SENSOR OVERLOAD DETECTION: XE2004 provides three programmable thresholds that allow detection sensory overload. Upon overload, output voltage XE2004 will saturate supply rail give pre-defined output voltage. SENSITIVITY SENSOR'S PARASITIC RESISTANCES: XE2004 accepts relatively parasitic resistors parallel with sensor's capacitances. example, parallel resistance kOhm parallel with sensor's capacitors will lead output error below POWER OPERATION: Several characteristics make XE2004 particularly suited battery operated applications: Low-power, low-voltage operation (2.4 power-on-reset function allows automatic uploading calibration data user settings from external non-volatile memory.
CONFIGURATION
Dimensions shown millimeters (inches) 3.30 (0.130)
2.70 (0.106)
XE2004I-SW number
identifier
Figure
XE2004I-SW SOIC (not scale)
Figure
location XE2004I-000 (not scale)
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Data Sheet prod number
DESCRIPTION
Position SOIC Position Name Type connected connected connected Analog Analog Logic Input Logic Input/Output connected Analog Analog Analog connected Power Analog Input Output Power Analog Analog Description
Power-on-reset signal Test output oscillator frequency Clock line data transfer Data line data transfer Upper electrode capacitive sensor Middle electrode capacitive sensor Lower electrode capacitive sensor Positive power supply Reference voltage (selectable input output) Negative power supply Connect optional filter capacitor Output signal
ABSOLUTE MAXIMUM RATINGS
Condition Voltage point with respect Storage temperature Minimum -0.3 Typical Maximum Unit
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Data Sheet XE2004
ELECTRICAL CHARACTERISTICS
Power supply operating temperature unless indicated otherwise. Symbol IVDD start-up time Note description power supply current consumption t_start type Unit comment
current consumption Ivdd varies with temperature supply voltage, according following expression temperature supply voltage
Ivdd(T,Vdd) [Ivdd( 27°C,2.4V) (Vdd 2.4V)] 0.005 27°C))
Note
Start-up time XE2004 only. This duration different when combined with non-volatile memory. Refer Application Note AN2004.01.
ANALOG SIGNAL PROCESSING CHAIN
TRANSFER FUNCTION XE2004 based digitally controlled, analog signal processing chain. provides amplified output voltage that function sensor capacitors CS2, various passive on-chip elements, supply voltage. passive on-chip elements trimmed digitally, thus allowing compensation sensor imperfections such offset non-linearity. IMPORTANT: C-to-V converter architecture does only read electrically floating capacitors CS2. connection pins another external element than electrically floating electrode will adversely affect operation. conversion sensor capacitances output voltage realized amplifier stages cascade. first stage, called C-to-V conversion stage, provides bits programmable (coarse) offset compensation through registers COFF, COFFP. also allows bits non-linearity compensation through registers CNOM, CDEN. second stage programmable gain amplifier with bits fine offset tuning register ROFF. Gain programmable over bits (registers GAINH, GAINL). sensor capacitors form capacitive half-bridge. CS2, XE2004 provides output signal that equals value internal reference voltage (suppose Voff zero). Therefore, expressing output signal REF, obtains output signal CS2.
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Data Sheet XE2004
overall transfer XE2004 given
VOUT VREF VREF Voff Ccomp
[Volt
Note that output voltage C-to-V conversion stage equal
VREF Ccomp
Ccomp CNOM CDEN
[Volt
with
Where: VREF
gain (inverting) programmable gain amplifier reference voltage REF, either equal (VDD VSS)/2 register SET.1 reset zero, default setting), provided externally SET.1 one). CS1+(1-).COFF; includes capacitances between pins register COFFP.0 reset (zero, default value), register COFFP.0 (one). CS2+.COFF; includes capacitances between pins register COFFP.0 reset (zero, default value), register COFFP.0 (one). Ccomp non-linearity compensation capacitor, determined on-chip capacitors CNOM, CDEN, programmable through registers CNOM CDEN, respectively. Voff offset voltage, referred input gain stage. Voff offsets contributed non-ideal amplifiers, offset introduced through registers COFF, COFFP ROFF.
RESOLUTION
output referred noise uV/sqrt(Hz) while input referred resolution 0.25e-18 F/sqrt(Hz) (0.42e-18 sqrt(Hz)
FREQUENCY RESPONSE
frequency response analog signal processing chain combination C-to-V stage programmable gain stage. gain stage determines overall bandwidth. cut-off frequency given this expression: [Hz] Bandwidth Rgain (Cgain CGext Where: gain programmable gain amplifier equals kOhm Variation over temperature +125 with respect cut-off frequency Cgain equals product Rgain*Cgain vary with respect nominal (designed) value. CGext value optional external capacitor connected between pins nominal value Bandwidth 17.3 CGext Rgain
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Data Sheet XE2004
electrical specifications analog signal path given Table below. Table 1Electrical characteristics analog signal path VDD-VSS unless specified otherwise. Symbol Description type Unit Sensor requirements Ctot Total value sensor capacitances Creldif Relative difference sensor capacitances Rpar Resistance parallel sensor capacitor Output voltage VOUT VOUT dynamic range TCvout Temperature variation µV/°C VOUT Svout White noise spectral -100 density VOUT dBV/H Voffres Output referred residual -1.1 offset Gain Gain Kstep Gain trim step 0.007 Ktol Nominal gain spread TCgain Temperature variation -150 ppm/°C gain External elements Rout External resistive load VOUT Cout External capacitive load VOUT CGext External filter capacitor 1000 Note comment Note Note Note
Note
Note Note Note Note
Note Note
Measured VOUT VGND. From drift VOUT increases maximum ppm/°C. Note Gain defined ratio between output signal VOUT input signal gain amplifier. Note Spread nominal value, before calibration. Note After offset trimming output stage. Voffres determined from VOUT AGND. Note External sensor. CS2. include potential wiring other paracitic capacitances. Note External sensor. relative difference defined (CS1 CS2) (CS1 CS2). Note maximum capacitive load VOUT defined load which second harmonic distortion reaches fundamental signal cut-off frequency. Note CGext parallel on-chip filter capacitor type. Note gain output stage programmable with 1023 equal steps 0.007 between Note precision VOUT. Rpar typically paracitic resistor related sensor construction. Rpar often specified other manufacturers, typically more than required assure precision. XE2004, however, special circuit technique, minimum value Rpar relatively low. precision, Rpar must 51.2 least. programmable gain amplifier drives loads kOhm
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Data Sheet XE2004
REFERENCE BUFFER AMPLIFIER
XE2004 converts difference capacitances into single-ended voltage VOUT. Positive negative output signals obtained referencing output signal VOUT GND. equals half supply voltage. characteristics reference buffer amplifier listed Table VDD-VSS Symbol description Vgnd Buffered reference voltage Rgnd External resitive load Cgnd External capacitive load Note type (VDD VSS)/2 Unit comment Note
Since VOUT VGND trimmed minimum offset, only typical value Vgnd specified. specifications, refer specification Voffres Table
Table 2Reference buffer amplifier characteristics
SENSOR OVERLOAD DETECTION
XE2004 sensor overload detection function. Sensor overload needs detected order avoid situation which output voltage saturates gets stuck VSS. This might lead unwanted condition closed loop control systems including XE2004. overload condition occurs, output signal will clipped predefined threshold level, instead VSS. OVTH register used program upper lower threshold levels, which symmetrical around AGND. Upon removing overload situation, will return normal reading. overload condition more following cases true: (CS1-CS2)/(CS1+CS2) input signal gain stage goes outside lower limit VDD-VSS under supply) input signal gain stage goes outside upper limit VDD-VSS under supply) upper lower threshold limits programmable different values. description OLTH register more details.
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Data Sheet XE2004
SERIAL INTERFACE
XE2004 2-wire serial interface read from writing internal registers. This interface used, instance, configure XE2004 during factory calibration sensor. serial interface also used upon power-up XE2004 combination with external non-volatile memory (refer application note AN2004.1). bi-directional oriented protocol implemented. XE2004 always slave. used clock data. bi-directional used transfer data registers. Read write commands preceded start condition, which high-to-low transition when high, Figure Because push/pull output, start cannot generated while XE2004 outputting data.
Figure
Definition start condition.
Figure
Definition data validity.
write operation initiated with start condition, Figure eight-bit control byte, which consists address bits bits command follow start condition. After receipt control byte, XE2004 will enter write mode wait data written into registers. data shifted into device next eight clock cycles. read operation initiated with start condition, also Figure eight-bit control byte, which consists address bits, bits command follow start condition. After receipt control byte, XE2004 will enter read mode prepare data read. data shifted device next eight clock cycles. While clocking data out, start condition cannot generated.
Figure
Write sequence (top) read sequence (bottom).
master must free prior pulse number allow XE2004 send data, figure below.
Figure
Read cycle timing.
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Data Sheet XE2004
EXTERNAL NON-VOLATILE MEMORY
external non-volatile memory used store bytes sensor-related data other settings that were obtained during sensor manufacturing. Upon power-up (POR high-to-low transition), XE2004 ready receive data lines. application based Microchip PIC12LC50x been developed. Program code available from XEMICS. detailed description, refer Application Note AN2004.1 DK2004 Development User Guide.
REGISTERS
XE2004 contains 8-bit registers that relate various programmable elements user settings. registers documented, registers reserved. From documented registers, registers related sensor calibration user settings, remaining ones related application debugging. summary registers given Table detailed description registers given further below. Address 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 0000 0001 0010 0011 0100 010101 1111 Name Reserved CDEN CNOML CNOMH COFF COFFP Reserved ROFF GAINL GAINH Reserved Reserved FOSC OVTH Reserved Reserved Reserved Reserved Reserved
CNOM ROFF GAINL6 GAINL GAINL5 GAINL4 GAINL3 GAINL2 GAINL1 GAINH1 GAINL0 GAINH0
CNOML ROFF6
CNOML ROFF5
CNOML ROFF4
CNOML COFF3 ROFF3
CDEN2 CNOML COFF2 ROFF2
EXTRE CDEN1 CNOML COFF1 ROFF1
EXTCK CDEN0 CNOML0 CNOMH0 COFF0 ROFF0
MOSC
FOSC3
FOSC2
FOSC1 OVTH1
FOSC0 OVTH0
PORF
Table 3Summary registers
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Data Sheet XE2004
CONFIGURATION REGISTER
EXTRE EXTCK
Default value
Res: Reserved bits These bits reserved should always contain default setting. EXTREF: External voltage reference (one) case external voltage reference connected REF. reset (zero) case internal reference voltage source used. EXTCK: External CLock (one) case external clock connected SCK. internal clock then disabled. reset (zero) internal clock used. INTEGRATION CAPACITOR (CF) REGISTER
Default value
-DC: Don't care bits These bits reserved. Integration Capacitor Value value capacitor programmable between (all bits reset) (all bits set) steps LSB, MSB. COMPENSATION CAPACITOR (CDEN) REGISTER CDEN
Default value CDEN2 CDEN1 CDEN0
Don't care bits These bits reserved. CDEN: Stability Capacitor Value value capacitor CDEN programmable between (all bits reset) (all bits set) steps CDEN0 LSB, CDEN2 MSB. Note: code CDEN 0000 0000 forbidden value. COMPENSATION CAPACITOR (CNOM) LOWER REGISTER CNOML
CNOML CNOML CNOML CNOML CNOML CNOML CNOML CNOML
Default value
CNOML: Linearity Capacitor Value, Lower Register value capacitor CNOM determined bits contained registers, CNOML CNOMH. CNOM programmable between (all bits reset) 51.1 (all bits set) steps CNOML0 LSB, CNOMH0 MSB.
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Data Sheet XE2004
COMPENSATION CAPACITOR (CNOM) HIGHER REGISTER CNOMH
CNOMH
Default value
Don't care bits These bits reserved. CNOMH: Linearity Capacitor Value, Higher Register value capacitor CNOM determined bits contained registers, CNOML CNOMH. CNOM programmable between (all bits reset) 51.1 (all bits set) steps CNOML0 LSB, CNOMH0 MSB. OFFSET CAPACITOR REGISTER COFF
Default value COFF3 COFF2 COFF1 COFF0
Res: Reserved bits These bits reserved should always contain default setting. COFF: Offset Capacitor Value value capacitor COFF determined bits. COFF programmable between (all bits reset) (all bits set) steps COFF0 LSB, COFF3 MSB. POLARITY OFFSET CAPACITOR REGISTER COFFP
Default value
Don't care bits These bits reserved. POL: Polarity Offset Capacitor polarity reset (zero), COFF connected parallel with sensor capacitor CS1. polarity (one), COFF connected parallel with sensor capacitor CS2. OFFSET RESISTOR REGISTER ROFF
Default value ROFF7 ROFF6 ROFF5 ROFF4 ROFF3 ROFF2 ROFF1 ROFF0
Offset Resistor ROFF value resistor ROFF determined bits. ROFF programmable between (all bits reset) 1.89 MOhm (all bits set) steps kOhm. ROFF0 LSB, ROFF7 MSB.
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Data Sheet XE2004
GAIN, LOWER REGISTER GAINL
Default value GAINL7 GAINL6 GAINL5 GAINL4 GAINL3 GAINL2 GAINL1 GAINL0
GAINL: Gain Setting, Lower Register value gain programmable gain amplifier, GAIN, determined bits contained registers, GAINL GAINH. GAIN programmable between (all bits reset) (all bits set) steps 6.84e-3. GAINL0 LSB, GAINH1 MSB. GAIN, HIGHER REGISTER GAINH
GAINH GAINH
Default value
Don't care bits These bits reserved. 1.0- GAINH: Gain Setting, Higher Register value gain programmable gain amplifier, GAIN, determined bits contained registers, GAINL GAINH. GAIN programmable between (all bits reset) (all bits set) steps 6.84e-3. GAINL0 LSB, GAINH1 MSB. OSCILLATOR FREQUENCY REGISTER FOSC
Default value FOSC3 FOSC2 FOSC1 FOSC0
Don't care bits These bits reserved. 3.0- FOSC: Oscillator Frequency Setting value internal oscillator trimmed around nominal value over bits. default nominal oscillator frequency kHz, programmable between (all bits reset) (all bits set) non-linear fashion. FOSC0 LSB, FOSC3 MSB. OVERLOAD THRESHOLD REGISTER OVTH
Default value OVTH1 OVTH0
Don't care bits These bits reserved. 1.0- OVTH: Overload Threshold Setting value overload threshold programmed four values, according following Table. Code disables overload protection. overload should happen code XE2004 will enter into lock situation output signal will stuck VSS. This situation only resolved through resetting XE2004.
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Data Sheet XE2004
OVTH1
OVTH0
Lower threshold limit VDD-VSS)
Upper threshold limit VDD-VSS)
MONITOR REGISTER
Default value MOSC
Don't care bits These bits reserved. Res: Reserved bits These bits reserved should always contain default setting. MOSC: Monitor Internal Oscillator Frequency value internal oscillator monitored when MEAS.4 (one). frequency program through register FOSC. Res: Reserved bits These bits reserved should always contain default setting. POWER-ON REGISTER
Default value PORF
Don't care bits These bits reserved. Res: Reserved bits These bits reserved should always contain default setting. PORF: Power-on Force This contains status power-on-reset signal POR. When PORF (one), logical high, when PORF reset (zero); logical low.
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Data Sheet XE2004
APPLICATION NOTES DEVELOPMENT TOOLS
following application notes development tools available from XEMICS: AN2004.01 AN2004.02 DK2004 Using PIC12LC50x microcontroller with memory store register values XE2004 Getting calibrated sensor steps Development XE2004
DK2004 XE2004 Development Kit. DK2004 suited evaluation XE2004 application, well manufacturing environment. DK2004 contains: Evaluation board sockets XE2004I-SW PIC12LC509A microcontroller interface board XE2004I-SW PIC12LC509A-04I/P Labview-based graphical user interface DK2004 requires National Instruments' PCI-6503 card (DIO-24).
DK2004: evaluation board interface board
DK2004: Graphical user interface
©XEMICS, 2001 rights reserved. Reproduction whole part prohibited without prior written consent copyright owner. information presented this document does form part quotation contract, believed accurate reliable changed without notice. liability will accepted publisher consequence use. Publication thereof does convey imply license under patent other industrial intellectual property rights
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