1.1 2 AS8500 Universal multi pupose data aquisition system 3 Preliminary Data Sheet DATA SHEET 1 2 3 Features 16 bits resolution differential inputs Single + 5V supply Low power 15 mW SOIC16 package Self- and system-calibration with auto-calibration on power up 16 kHz maximum sampling frequency internal temperature measurement internal reference programmable current sources digital comparator active wake-up PGA gains 6, 24, 50, 100 Zero offset Zero offset TC Extremely low noise Internal oscillator with comparator for active wake up 3-wire serial interface, μP compatible temperature range – 40 to + 125 °C Applications battery management for automotive systems power management mV/µV-meter thermocouple temperature measurement RTD precision temperature measurement high-precision voltage and current measurement General description The AS8500 is a complete, low power data acquisition system for very small signals (i.e. voltages from shunt resistors, thermocouples) that operates on a single 5 V power supply. The chip powers up with a set of default conditions at which time it can be operated as a read-only-converter. Reprogramming is at any time possible by just writing into two internal registers via the serial interface. The AS8500 has four ground refering inputs which can be switched separately to the internal PGA. Two input channels can also be operated as a fully differential ground free input. The system can measure both positive and negative input signals. The PGA amplification ranges from 6 to 100 which enables the system to measure signals from 7mV to 120 mV full scale range with high accuracy, linearity and speed. The chip contains a high precision bandgap reference and an active offset compensation that makes the system offset free (better than 0,5 μV) and the offset-TC value negligible. The builtin programmable digital filter allows an effective noise suppression if the high speed is not necessary in the application. The input noise density is only 35 nV / Hz and due to Revision 1.1, 04-April-06 AGND REF INTERNAL TEMPERATURE ETR ETS VBAT VDDA VSSA 1.26 V REFERENCE VDDD CALIBRATION DATA BUF VSSD INPUT MUX DSP CONTROLLER FILTER INT. CLOCK TIMER CHOPPER 16 BIT - CONVERTER PROTECTION RSHH PGA and LEVEL SHIFT RSHL CURRENT SOURCES CLK EZPRG COMPARATOR SERIAL INTERFACE / CONTROL REGISTERS SCLK SDAT INTN Figure 1: Functional Block Diagram the high internal chopping frequency the system is free of 1/f-noise down to DC.The 0-10 Hz noise is typical below 1 µV i.e. as good or better than any other available chopper amplifier. For high speed synchronous measurements the chip can run in an automatic switching mode between two input channels with preprogrammed parameter sets. The circuit has been optimised for the application in battery management systems in automotive systems. As a front end data acquisition system it allows an high quality measurement of current, voltage and temperature of the battery. With a high quality 100 μΩ resistor the system can handle the starter current of up to 1500 A, a continuous current of ± 300 A as well as the very low idle current of a few mA in the standby mode. For external temperature measurement the chip can use a wide variety of different temperature sensors such as RTD, PTC, NTC, thermocouples or even diodes or transistors. A built-in programmable current source can be switched to any input and activate these sensors without the need of other external components. The measurement of the chip temperature with the integrated internal temperature sensor allows in addition the temperature compensation of sensitive parameters which increases the total accuracy considerably. The flexibility of the system is further increased by a digital comparator that can be assigned to any measured property (current, voltage, temperature) and an active wake-up in the sleep-mode. All analog input-terminals can be checked for wire break via the SDIinterface. www.austriamicrosystems.com Page 1 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet CONTENTS 1 FEATURES.........................................................................................................................................................................................1 2 APPLICATIONS .................................................................................................................................................................................1 3 GENERAL DESCRIPTION.................................................................................................................................................................1 4 PIN FUNCTION DESCRIPTION FOR SOIC 16 PACKAGE...............................................................................................................3 5 ABSOLUTE MAXIMUM RATINGS.....................................................................................................................................................4 6 ELECTRICAL CHARACTERISTICS ..................................................................................................................................................5 7 FUNCTIONAL DESCRIPTION ...........................................................................................................................................................9 7.1 POWER ON RESET ...........................................................................................................................................................................9 7.2 ANALOG PART, GENERAL DESCRIPTION .............................................................................................................................................9 7.2.1 Reference voltage .............................................................................................................................................................10 7.2.2 Current sources.................................................................................................................................................................11 7.2.3 Internal temperature sensor ..............................................................................................................................................12 7.3 DIGITAL PART .................................................................................................................................................................................12 7.3.1 Sampling rate ....................................................................................................................................................................12 7.3.2 Calibration .........................................................................................................................................................................12 7.4 MODES OF OPERATION ...................................................................................................................................................................13 7.5 REGISTER DESCRIPTION .................................................................................................................................................................14 7.5.1 OPM operation mode register ( 4 bits ) .............................................................................................................................15 7.5.2 CRG general configuration register ( 28 bits )...................................................................................................................15 7.5.3 CRA measurement channel A configuration register ( 17 bits ) ......................................................................................16 7.5.4 CRB measurement channel B configuration register ( 17 bits ) .......................................................................................18 7.5.5 ZZR Zener-Zap register (188 bits ):..................................................................................................................................19 7.5.6 CAR calibration register ( 110 bits ) .................................................................................................................................21 7.5.7 TRR trimming register ( 20 bits ) .......................................................................................................................................21 7.5.8 THR alarm (Wake-up) threshold register ( 17 bits ) .........................................................................................................24 7.5.9 MSR measurement result register ( 18 bits )....................................................................................................................24 8 DIGITAL INTERFACE DESCRIPTION.............................................................................................................................................24 8.1 CLK..............................................................................................................................................................................................24 8.2 INTN ............................................................................................................................................................................................24 8.3 SDI BUS OPERATION ......................................................................................................................................................................25 8.4 DATA TRANSFERS ..........................................................................................................................................................................26 8.5 SDI BUS TIMING .............................................................................................................................................................................27 8.6 SDI ACCESS TO OTP MEMORY........................................................................................................................................................28 8.6.1 ZZR register bit mapping...................................................................................................................................................28 8.6.2 Stored ZZR-register mapping............................................................................................................................................32 9 GENERAL APPLICATION HINTS ...................................................................................................................................................33 9.1 GROUND CONNECTION, ANALOG COMMON .......................................................................................................................................33 9.2 THERMAL EMF ..............................................................................................................................................................................33 9.3 NOISE CONSIDERATIONS .................................................................................................................................................................33 9.4 SHIELDING, GUARDING....................................................................................................................................................................34 10 TYPICAL PERFORMANCE CHARACTERISTICS ..........................................................................................................................35 11 PACKAGE DIMENSIONS ................................................................................................................................................................37 12 REVISION HISTORY........................................................................................................................................................................37 13 ORDERING INFORMATION ............................................................................................................................................................37 14 CONTACT.........................................................................................................................................................................................38 14.1 HEADQUARTERS .......................................................................................................................................................................38 14.2 SALES OFFICES ........................................................................................................................................................................38 Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 2 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 4 PIN function description for SOIC 16 package PIN Name description 1 RSHL anlalog input from shunt resistor low side 2 RSHH anlalog input from shunt resistor high side 3 ETS analog input with reference to RSHL Comment analog common for VBAT, ETS and ETR; return for internal current source analog input for differential input ETS-VBAT analog output for current-source 4 VBAT analog input with reference to RSHL analog input for differential input ETS-VBAT analog output for current-source 5 VSS 0V-power supply for analog part 6 EZPRG digital power input for programming Zener fuses. 7 VSSD 0V-power supply and ground reference point for digital part This input must be open or connected to VDDD. It is not intended, that OTP content is modified by the user. digital input for external clock, master clock input external clock typical 8.192 MHz; during MWU-mode (see 7.4) external connection must be high impedance or connected to VDDD to reduce current consumption SCLK serial port clock input for SDI-port the user must provide a serial clock on this input SDAT serial data in- and output INTN Digital I/O for interrupt from comparator signal wake-up to external µC conversion ready flag for external interupt and synchronisation in normal mode 8 CLK 9 10 11 12 VDDD + 5V digital power supply 13 VDDA + 5V analog power supply 14 REF reference input/output 15 AGND analog ground, ground reference for ADC 16 ETR analog input with reference to RSHL must be connected to VSS with a 30 nF capacitor this PIN must be connected with a 50-100nF-capacitor to VSS; no direct connection to VSSD/VSS allowed analog output for current-source Table 1: Pin Description Figure 2: Schematic Package outline SOIC 16 Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 3 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 5 Absolute Maximum Ratings Stress beyond those listed under “Absolute Maximum Ratings“ may cause permanent damage to the device. These are stress ratings only. Functional operation of the device at these or any other conditions beyond those indicated under “Operating Conditions” is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. All voltages are defined with respect to VSS and VSSD. Positive currents flow into the IC. Absolute maximum ratings (TA = -40°C to 125°C unless otherwise specified) Nr. 0 1 2 PARAMETER Supply voltage Analogue VDDA and digital VDDD Input pin voltage SYMBOL VDD MIN -0.3 Vin TYP MAX 7.0 UNIT V -0.3 VDD +0.3 V ISCR -100 100 mA 3 Input current (latch-up immunity) Electrostatic discharge ESD -2 2 kV 4 Ambient temperature TA -40 125 OC 5 6 7 8 9 Storage temperature Soldering conditions Humidity, non-condensing Thermal resistance Power dissipation TSTRG TLEAD -55 150 260 85 75 350 OC 5 RthJA PTOT °C % K/W mW NOTE Polarity inversion externally protected JEDEC 17 1) (Tj = 150°C) 2) Notes: 1) MIL 883 E method 3015, HBM: R =1.5 kΩ, C =100pF. 2) Jedec Std – 020C, lead free Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 4 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 6 Electrical characteristics VDDA=5V +/-0.1 V, fclk=8.192 MHz, chopping ratio MM=4 (see 7.5.3), oversampling frequency=2.048 MHz, oversampling ratio=128 temperature range : -40 to 125°C if not otherwise noted symbol parameter conditions min typ max units input characteristics for gain 1 the input signal is connected directly to th input of the converter, this is not possible for the RSHH-RSHL G1 input Gain gains of PGA 6, 24, 50, 100 AC_g6 Accuracy at gain 6 0 to 85 °C 0.4 % @-120mV -40 to 125°C 1.0 % @-120mV AC_g24 Accuracy at gain 24 0 to 85 °C 0.2 % @+-20mV -40 to 125°C 0.6 % @+-20mV AC_g50 Accuracy at gain 50 0 to 85 °C 1 % @+-10mV AC_g100 Accuracy at gain 100 0 to 85 °C 1 % @+-5mV Vin input voltage ranges G1 -300 to + 800 mV (with reference to RSHL) G6 +/- 120 mV G24 +/- 30 mV G50 +/- 15 mV G100 +/- 7.5 mV 1) 2) 2),3) 2) 2) 3) 2)4) 2)4) 5) 6) 6) 7) 7) Notes: 1) the absolute gain values are subjected to a manufacturing spread of +/-30% 2) Accuracy relies on bandgap characteristic, on the gain variation over temperature and on the trimm information. To achieve optimum performance, the circuit may be trimmed by the user for best temperature stability by writting aproporiate data to the TRR register (see sections 7.4 and 7.5) Default content of TRR register is 17. 3) due to a nonlinear behaviour of the gain and reference voltage over temperature the accuracy is lower for the extended temperature range. 4) It is recommended to use these gain settings only for applications in the temperature range 0 t0 85°C therefore it is recommended to use these gain settings only for applications in the temperature range 0 to 85°C. 5) this gain range is not using the internal PGA, the input is directely connected to the AD-converter. Therefore the input resistance is lower then for other gain ranges. It has been designed mainly for positive input voltages up to 0.8 V i.e. for measurements of temperature with transistors and diodes. The limitation for negative input voltages is due to the onset of conduction of the input protection diodes. 6) the ASIC is optimised for G6 and G24 concerning linearity, speed and TC, therefore these ranges are recommended whenever possible. 7) because of higher TC value at elevated temperature G50 and G100 are recommended for applications in the temperature range 0 to 85°C Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 5 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet Electrical characteristics (continued) VDDA=5V +/-0.1 V, fclk=8.192 MHz, chopping ratio MM=4 (see 7.5.3), oversampling frequency=2.048 MHz, oversampling ratio=128 temperature range : -40 to 125°C if not otherwise noted symbol cal_err lin_err lin_errTC Vos dVos/dT Ib Vndin Indin en p_p en_RMS SNR SDR CCI PSRR parameter calibration error for 30 000 digits output at full range nonlinearity TC of linearity error offset voltage: RSHH_RSHL offset voltage: ETS, ETR, VBAT Offset voltage drift: RSHHRSHL input bias/leakage current, all channels voltage noise density (G=24) current noise density (G=24) voltage noise, peak (G=24) conditions min G1, 720 mV G6, 120 mV G24, 30 mV G50, 15 mV G100, 7.5 mV gain 6 @ room temp gain 24 @ room temp gain 50 @ room temp gain 100 @ room temp all gains typ max Device is not factory calibrated 0.1 0.03 0.05 0.05 1 units % 5 % or 30 digits % or 10 digits % or 15 digits % or 20 digits ppm/K 1) 2) 2) 2) 2) 3) -40 to 125°C -0.5 0.2 0.5 µV 4) -40 to 85°C 85 to 125°C -2 -4 0.5 1 1 2 µV µV 4) -40 to 85 °C room temperature 0.002 -1000 f=0 to 1 kHz f=10 Hz 0 to 100 Hz 0 to 10 Hz voltage noise, RMS (G=24) 1000 Hz signal to noise (G=24, G=6) room temperature signal to distortion (G=24, G=6) room temperature chanel to chanel insulation room temperature power supply rejection ratio 4.9 to 5.1 V 4) µV/K 0.2 1000 nA 5) 35 50 nV//Hz 6) 20 3 1 1.5 100 fA//Hz µV µV µV dBmin 6) 100 -90 -60 dBmin dBmax dBmax 6) 6) 6) Notes: 1) The output response might be calibrated by the user by writing appropriate calibration constants to the CAR register (see 7.5. ). The default values are 1548 dec 2) whatever is lower 3) max limit is derived fromdevice characterization and not tested 4) Min/Maximum limits over temperature range are derived from device characterization and not etsted. In normal operation a termperature independent digital offset of -0.7 digits is present due to internal raunding. 5) Typical leakage current is valid for all gain settings except G=1 for positive input voltages below 200 mV. In the temperature range 85-125°C it may be as high as 5 nA. In normal operation a temperature independent digital offset of -0.7 digits is present due to internal rounding. 6) This parameter is not measured directly. It is measured indirectly via gain measurement of the whole path at room temperature Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 6 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet Electrical characteristics (continued) VDDA=5V +/-0.1 V, fclk=8.192 MHz, chopping ratio MM=4 (see 7.5.3), oversampling frequency=2.048 MHz, oversampling ratio =128 temperature range : -40 to 125°C if not otherwise noted symbol parameter conditions min typ max units data conversion RES resolution all channels 16 bits Vref reference voltage room temperature 1.21 V 0-85°C,box Vref_TC temperature coefficient of Vref method 20 ppm/K Vref_Ri internal resistance of Vref Rload > 50 kOhm 200 Ohm fovs clock frequency 4.096 MHz R1 oversamplig ratio 64 128 MM conversions during chopper cycle 4 8 BW bandwidth 7.8 1000 16000 Hz av internal averaging 1 4 1024 cycles fclk external clock frequency 0.05 8.192 10 MHz CLK_extdiv clock division factor 2 4 DR_clk duty ratio of external clock 50 % int_fclk internal clock frequency 180 250 330 kHz analog inputs RSHH, VBAT, ETS, ETS Rin input resistance Ue < 150 mV 50 100 MOhm Cin input capacitance at gain 24 8 15 30 pF internal temperature sensor T_out20 output at 23°C G 6, typical 23 000 digits T_sl slope -20 to 100°C 75 digits/degC current source output to RSHH, RSHL Icurr_rshh 2 µA 1) 2) 3) 4) Notes: 1) with external averaging the resolution can be increased up to 21 bits with an effective sampling rate below 10 Hz 2) the system works in overflow condition without degradation of accuracy up to 1.4 * range width. This means that the overflow bit can work as bit no.17 in this range. 3) TC- value of the reference voltage may be set through trimm bits intentionally higher to minimize TC of the entire measurement path for gain 24 4) in the temperature range 0 - 85°C the clock frequency can be increased to 12 MHz Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 7 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet Electrical characteristics (continued) VDDA=5V +/-0.1 V, fclk=8.192 MHz, chopping ratio MM=4 (see 7.5.3), oversampling frequency=2.048 MHz, oversampling ratio=128 temperature range : -40 to 125°C if not otherwise noted symbol parameter conditions min typ max units programmable current source output to Vbat, ETS, or ETR Icurr_ON current level 0 248 µA I_steps current steps 6 8 10 µA TC_CS temperature coefficient 900 ppm/K Icurr_OFF current when off room temperature 0.001 µA Icurr_Ri internal resistance of current source Ua < 2 V 10 MOhm digital CMOS inputs with pull up and schmidt-trigger input PINs CLK and SCLK Vih high level input voltage VDDD=5V 3.5 V Vil low level input voltage VDDD=5V 1.5 V Iih current level VDDD=5V, Vih=5V -1 1 µA Iil current level VDDD=5V, Vil=0 30 120 µA digital CMOS outputs output PINs SDAT and INTN Voh high level output voltage VDDD=5V, -633uA 4.5 V Vol low level output voltage VDDD=5V, 564uA 0.4 V Cl capacitive load 20 pF Tristate digital I/O Voh high level output voltage VDDD=5V, -633uA 4.5 V Vol low level output voltage VDDD=5V, 564uA 0.4 V tristate leakage current to Ioz VDDD,VSSD VDDD=5V -1 1 µA Vih high level input voltage VDDD=5V 3.5 V Vil low level input voltage VDDD=5V 1.5 V supply current Isup normal operation VDDD=VDDA=5V 3 5 mA Iaw active wake-up VDDD=VDDA=5V 40 100 µA supply voltage VDDA positive analog supply voltage 4.7 5.0 5.3 V VDDD positive digital supply voltage 4.5 5.0 5.5 V VSS, VSSD negative supply voltage 0 V Power On Reset Vporhi Power on reset Hi 3.1 V Vhyst Hysteresis 0.2 V 1) 2) Notes: 1) the average current is dependent on the on-time of the measurement system i.e. it can be programed via the CRA register 2) dynamic stability of analog supply should be within +/- 0.1 V Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 8 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 7 Functional Description 7.1 Power on Reset The power on reset is iniciated during each power up of the ASIC and can be triggered purpously by reducing the analog supply voltage (VDDA) to a value lower than Vporlo for a time interval longer than 0.5 µsec. During power on reset sequence the following steps are performed automatically: The chip goes to mode MZL (see 7.4) Internal clock is enabled The calibration constants are loaded from Zener-zap memory to the appropriate registers (ZTR=>TRR, ZCL=>CAR). The load procedure is directed by the internal clock and can be monitored on INTN pin. 188 clock pulses are generated from the internal oscillator source. Pulse period is equal to internal clock period. After the power-on reset sequence is finished: the operation continues with internal clock if no external clock is detected. In this case the ASICs switches to mode MWU with default value of threshold register ( 214 ) If external clock is available the ASIC switches to mode current measurement MMS (default measurement with default configuration: gain=100, fovs=4.096MHz, R1=64, MM=4, R2=1, NTH=214). The microcontroller can communicate via SDI interface whenever appropriate, i.e. CAR and TRR register can be rewritten from the µC if necessary. Because the automatic selected calibration factor (CGI4) is loaded with zeros, the ASIC delivers constant zero at the output to allow the µC to check for an unwanted POR. To bring the ASIC back into normal operation for current measurement with gain100 the µC has to copy the CAU4 default content or a customer specific calibration factor into the CAR-register. (see also 7.5.5 and 8.6.2) 7.2 Analog part, general description The input signals are level shifted to AGND (+ 2.5 V) then switched by the special high quality MUX- which contains also the chopper – to the input of the programmable gain amplifier (PGA). This low noise amplifier is optimised for best linearity, TC- value and speed at gain 24. The systems contains an internal bandgap reference with high stability, low noise and low TC-value. The output of a programmable current source can be switched to the analog inputs VBAT, ETS and ETR for testing the sensor connections or for external activation of resistors, bridges or sensors (RTD, NTC). The voltage drop generated by the current is measured at the corresponding input/output PIN. For the wire break test of the RSHH and RSHL inputs special low noise current sources are implemented. The integrated temperature sensor can also be switched to the PGA by the MUX and measured any time. The chip temperature can be used for the temperature compensation of the gain of the different channels in the external µC, which increases the absolute accuracy considerably. The offset of the amplifier itself is already fairly low, but to guarantee the full dynamic range it can be trimmed via the digital interface to nearly zero independent of the autozero chopping function. In the same way the manufacturing spread of the absolute value of the reference voltage can be eliminated and the TC-value set to nearly zero by a trimming process via the SDI interface. For more details of the input multiplexer see the following schematic. The position of all switches is defined by writing into the registers CRA, CRB and CRG via the SDI bus, which is explained in 7.5.2 through 7.5.4. M7 M6 INTERNAL TEMPERATURE CURRENT SOURCE ETR M9 M8 ETS M 15 M2 M 14 VBAT M 10 M4 M3 M5 RSHH M1 RSHL PGA ADCONVERTER M 12 M 13 Figure 3: Multiplexer Revision 1.1, 04-April-06 AUXILIARY CURRENT SOURCE www.austriamicrosystems.com Page 9 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 7.2.1 Reference voltage The ASIC contains a highly sophisticated precision reference voltage. Its typical temperature dependence is a slight parabola shaped curve and is shown in figure 14. This reference voltage is used mainly for the internal AD-converter, but can also be used for external purposes if the impedance of the external circuitry is high enough. reference voltage as function of resistance load 1,26 reference voltage in V 1,24 1,22 1,20 1,18 measurement open loop value 1,16 1,14 1,12 10 20 30 40 50 60 70 80 90 100 110 resistance load in kOhm The absolute value and its temperature coefficient (TC) is given by the content of the TRR register. This opens the possibility to calibrate the reference voltage to the optimum absolute value (i.e. 1.28 V) and the TC value to zero thus eliminating fully the production spread. Writing into subregister TRIMBV of TRR changes the absolute value linearly by 5.1 mV per digit as shown in the following graph and described in full detail in 7.5.7 as function of temperature reference voltage in V 1,36 1,32 75 °C 24 °C 1,28 1,24 1,20 1,16 0 5 10 15 20 25 30 content of TRIMBV in bits Trimming the TC value is similarly done by writing into subregister TRIMBTC. Since the TC trimming is also changing the absolute value it is important to trim the TC first and then the absolute value. Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 10 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet temperature coefficient as function of TRIMBTC setting temperature coefficient in ppm/K 200 150 100 change 12.7 ppm/K per step 50 0 -50 -100 -150 -200 -250 0 5 10 15 20 25 30 35 setting of subregister TRIMBTC of TRR The TC trimming also opens the unique possibility to change the TC-value within the time of reprogramming of the TRR-register (i.e. within µsec) to allow the compensation of different TC-values of the external circuitry for different channels. In addition it can be used for very fast autocalibration of the total TC of a given channel. An external reference voltage is applied to the channel to be checked. Then all numbers from 0 to 31 are written into subregister TRIMBTC and a reading is done for the input voltage and the internal temperature as well. The same is repeated at any temperature above RT. From these data the TRIMBTC setting for a minimum drift can be easily calculated. 7.2.2 Current sources The AS8500 contains several current sources which can be used for checking all input lines for wire brake, to control external circuitry or to activate external sensors. Main current source The main current source can be digitally controlled via the content of the CRG register in 31 steps of 8 µA in the range of 0 to 248 µV. Its absolute value can be calibrated by writing in the subregister TRIMC of TRR. The current source can be switched to the inputs VBAT, ETR or ETS to activate external sensors like RTDs, NTCs or resistance briges and strain gages. It can also be used to detect a wire breake of external connected sensors. Performing a measurement with a high and a low (or zero) current opens the possiblity to eliminate thermal EMF voltages in external sensors. Secondary current sources The ASIC contains two other high quality current sources supplying a current of approx. 2µA at the inputs RSHL and RSHH. These current sources can be switched on and off at any time to check the correct connection of both terminals. During off state they must not interfere with the high sensitive voltage inputs, especially the noise level should not be increased. If one of the terminals is an open connection the amplifier goes into saturation and the overflow bit is set. Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 11 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 7.2.3 Internal temperature sensor The ASIC contains a high sensitive precision temperature sensor which can be used at any time. The sensor supplies a very linear voltage with temperature. The voltage can be measured using the internal circuitry with gain 6, with free selection of all other parameters defining the sampling rate. In the dual mode (see 7.4 mode 2) the ASIC is switching automatically between the two channels and it needs at least one measurement for each polarity to get a valid measurement. In addition the ASIC needs some time to reprogram the internal registers and switches. Therefore the maximum sampling frequency is limited to 7.5 kHz for the above measurement of internal temperature sensor over oil bath temperature 35000 100 50 25 25000 0 -25 20000 -50 output signal linearity deviation inearity deviation in digits internal temperature in digits 75 30000 -75 cubic fit 15000 -100 -50 -25 0 25 50 75 100 125 150 175 temperature in deg C The slope of the curve is approx. 75 digits per degC. given clock frequency. The internal averaging is not working in the dual mode, but the sampling frequency can be different for each channel. The calculation of the temperature has to be done in the external µC acc. to the following simple formula: 7.3.2 Tint=( Uint(T)-Uint(23) ) / 75 + 23°C Uint(T) is the measured result and Uint(23) is the reference value at 23°C, which is stored as an 11 bit-word in the ZZR-register. 7.3 The calibration of the ASIC is done by a test setup as follows: room temperature calibration of the internal temperature sensor absolute input-output calibration for all gain settings TC calibration for the measurement path for gain 24 The absolute input-output calibration of the gain ranges can be done that way that for a given input voltage 30 000 digits at the output are produced: Digital part In the digital part the result of the AD-converter is processed, i.e. calibration, active offset cancellation and filtering is done. In addition the communication via the serial SDI interface is handled and all circuit functions (like voltage and current path settings, chopping, dechopping) are controlled. Whenever the power supply line returns from below POR threshold a power-up circuitry is activated which loads the internal calibration registers from the Zener-Zap memory into the working register and starts the chip in a special default mode. 7.3.1 Calibration Table 7.2.2 gain input/mV output/digits 1 6 24 50 100 720 120 30 15 7.5 30 000 30 000 30 000 30 000 30 000 Sampling rate the sampling rate (SR) is defined by the setting of parameters in register CRA or CRB. The oversampling frequency (OSF), the oversampling ratio (OSR), the chopping ratio (MM) and the averaging number (AV). The sampling rate can be calculated acc. to the following formula: SR= OSF/(OSR*MM*AV) The TC-value of the output (total measurement path) for G24 can be trimmed to a minimum value by selecting the best setting of the TRIMBTC subregister of the TRR register (see 7.5.7). A factory calibration is done for the amplifier offset (TRIMA). This data is stored in the ZZR register. ZZR-register mapping is given in 8.6.2 For an clock frequency of 8.192 MHz it can vary between 16 000 Hz and 1.95 Hz. Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 12 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 7.4 Modes of operation The AS8500 can run in different operation modes, which are selected and activated via the serial interface. Detailed description: Mode 0: MZL In power-on reset sequence, which is initiated by the on-chip power-on reset circuit whenever the power is connected , the registers are loaded from the Zener-Zap memory. Mode 1: MMS Measurement mode where the definition is taken from the registers CRA and CRG defined later on. The measurements are continuous and measured results are available after the ready flag (INTN pin) is set to LO. The result can be read by the µC any time after this bit is set to LO. However, to obtain the best noise performances the result should be read when INTN pin is at LO state. All modules are in power-up. Mode 2: MMD Dual channel measurement mode. Two consecutive different measurements are performed according to the settings in the configuration registers CRA, CRB and CRG defined later (usually CRA defining current measurements and CRB voltage measurement). One complete measurement is performed with each setting. CRG register holds common settings. The measurements are continuous (A,B,A,B). The 17th bit in the output register defines, which measurement has been executed according to the definition LO=A, HI=B. The number of consecutive measurements with equal configuration is defined in register CRG (bits s3,s2,s1,s0). All modules are in power-up. Mode 3: MWU In this wake-up mode the internal clock finclk=256kHz is running and one complete measurement is performed in the period from 1 to 1.5 s with the parameter settings of the CRA register. Before the actual measurement is performed the logic powers up all internal circuits especially the AGND and the Vref. If the external load is higher than 70 kOhms both signals can be used for external triggering or even as interrupt for the µC. If the external clock is not running, this input should be high impedance. To achieve a stable low idle current the oversampling ratio should be set to R1=128 and the CFG register must be programmed to x00003, see also 7.4 ‘Register description’. It is assumed that the threshold level in the THR register is defined within the 16 bit range, if not the default value is 210 After one measurement is finished all modules except the on- board oscillator and divider are switched into power down condition to save power. The MSR register is updated with the last measurement result. Whenever this value exceeds the digital threshold the (wake-up) INTN pin goes LO for one clock cycle to trigger the wake-up event in the external µC. After that the circuit returns in power-down for approximately 1s. During this time the last measurement (MSR register) is available on the SDI interface. In this intermediate sleep-mode all modules except internal oscillator and divider are in power-down mode. The SDI interface works independent which means that the measurement result is available by reading the MSR register. At any time the microprocessor can start any other mode via SDI. In such a case the external clock must be switched on first. The chip goes in MWU mode (mode 3) after it received the command for that. After that command 6 or more additional CLK pulses are needed before external clock may go to power down mode (no CLK pulses, high level because of internal pull-up resistors). This 6 CLK pulses are needed for synchronisation. On the way back to normal mode this restriction is not needed. Mode 4: MAM In this alarm mode the measurement defined in CRA is going on. The channel bit in the THR register must be cleared (channel A). The threshold value may be positive or negative. Whenever the measured value exceeds the digital threshold value in the THR register the pin INTN (in this mode its function is to signal alarm-condition) goes LO for one clock cycle. For negative threshold value the signed measurement result must be more negative than the THR value to activate the alarm. During measurements the signal INTN is high. All modules are in power-up, measurements are continuously going on. Mode 5: MZP Zener-Zap programming/reading. This mode for factory programming only and should not be used by the customer. Mode 6: MPD Power down mode. Individual analog blocks can be disabled/enabled. The data acquisition system is not running during this mode is activated. Mode 7: MSI The operation in this mode is exactly the same as in MMS mode except that the internal clock is used. The SDI interface signals can become active whenever appropriate. This mode can be used if no external clock CLK is available. The measuring speed is reduced by a factor of 16. Modes 8-15: These modes are reserved for testing purposes and should not be used by the customer. Reading and writing of some registers is only possible in these higher modes. Write to registers CAR (calibration register) and TRR (trimming register) is allowed only in test modes. Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 13 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet Modes of operation, register OPM Mode 0 Name MZL 1 MMS 2 MMD 3 Description Power on, loading from Zener-Zap memory Single measurement mo3 0 mo2 0 mo1 0 mo0 0 0 0 0 1 0 0 1 0 MWU Double measurement (A,B,A,B …) Wake-up 0 0 1 1 4 MAM Alarm 0 1 0 0 5 MZP Zener program/read 0 1 0 1 6 MPD Power down 0 1 1 0 7 MSI 0 1 1 1 1 x x x 8-15 Reserved for testing 1) Notes: 1) Register addresses 12, 13, 14 and 15 are reserved for testing and future options; operations on these registers must be avoided 7.5 Register description In the following sections the register contents and their functions are described in detail. Since the length of some registers is too long to present clearly, the registers are logically subdivided according to their functions and described separately. All internal functions are controlled by the contents of these registers which can be reloaded via the serial SDI interface at any time. The AS8500 contains the following registers: REGISTER ADDRESS SIZE OPM 0 4 Operating mode register 7.5.1 CRA 1 17 Measurement A configuration register 7.5.3 CRB 2 17 Measurement B configuration register 7.5.4 CRG 3 28 General configuration register 7.5.2 MSR 4 18 Measurement result register 7.5.9 ZZR 5 188 Zener-Zap register 7.5.5 CAR 6 110 Calibration register 7.5.6 TRR 7 20 Trimming register 7.5.7 THR 8 17 Alarm or wake-up threshold register 7.5.8 CFG 9 20 Test and special configuration register reserved 10-12 Note: 1) Contents Detailled description see 1) Test registers This register is reserved for testing modes. Writing is possible only in mode 8. In order to assure stable conditions in power-down modes MWU(3), MPD(6), TMSS(8) and MSI(13) the default setting of the CFG register must be changed to x00003. It is not necessary to change this value during normal operation. Write commands not supported in a certain mode can be released immediately after the register address. The ASIC will resume operation with the next start condition. Registers CAR and TRR are not buffered. Any read operation of the CAR or TRR register may generate transients in the analog circuitry; further accurate measurements require a delay time for settling. Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 14 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 7.5.1 no. 0 1) OPM operation mode register ( 4 bits ) Bit default mo3 0 mo2 0 mo1 0 mo0 0 Note 1) This register has been described in detail under 7.4 7.5.2 no. 0 CRG general configuration register ( 28 bits ) CRG bits 27-22 CRS 21-11 CRI 10-7 CRV 6-0 CRP NOTE subregister CRS: Sequence length, dechop and chop ( 6 bits ) Nr. 0 1 Bits CRS bit names Default 5 s3 4 s2 3 s1 2 s0 1 d 0 c 0 0 0 1 1 1 NOTE 1) 2) Notes: 1) This register defines the sequence length, chopping (c) and dechopping (d) of the input signal 2) Default power-up state before any setting Sequence length bits ( 4bits) Nr. 0 No. of measurements 16 s3 0 s2 0 s1 0 s0 0 1 1 0 0 0 1 … … … … … … 14 14 1 1 1 0 15 15 1 1 1 1 NOTE 1) default Notes: 1)Number of consecutive measurements of A and B with settings defined in CRA,CRB and other settings in CRG register. This setting is used only for mode MMD. DECHOPPING BIT Nr. 0 Dechopping No dechopping d 0 1 Dechopping 1 Nr. 0 Chopping No chopping c 0 1 chopping 1 NOTE CHOPPING BIT NOTE subregister CRI: Current configuration ( 11 bits ) Nr. 0 10 M14 9 M13 8 M12 7 M11 6 M8 5 M6 4 i4 3 i3 2 I2 1 i1 0 i0 1 Bits CRI bit names Default 0 0 0 0 0 0 0 0 0 0 0 2 output VBAT RSHL RSHH no ETS ETR NOTE 1),3) 2) Notes: 1) whenever M1=1 in (CRA,CRB) it is good practice to set all M6 to M14 to zero, but it is not mandatory 2) default logic state after power up and before any setting 3) All bits with names M14 to M1 represent control signals of the multiplexer with positive logic (for example M14=1 means that corresponding switch is closed). Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 15 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet Current source setting bits (5 bits) Nr. 0 Current [uA] 0 i4 0 i3 0 i2 0 i1 0 i0 0 1 8 0 0 0 0 1 2 16 0 0 0 1 0 3 24 0 0 0 1 1 4 32 0 0 1 0 0 … … … … … … 31 248 1 1 1 1 1 NOTE subregister CRV: Voltage configuration (4 bits ) Nr. 0 3 M15 2 M10 1 M9 0 M7 1 Bits CRV bit names Defaults NOTE 0 0 0 0 2 channel VBATRSHL VBAT-ETS differential ETS-RSHL ETRRSHL 1),3) 2) Notes: 1) This register defines the connection of the analog voltage- bus to the input-PINs and to the A/D converter 2) Default logic state after power-up and before any setting subregister CRP: Power down configuration ( 7 bits ) Nr. 0 1 Bits CRP bit names Defaults 2 block p6 pdosc p5 pda p4 pdm p3 pdb p2 pdc p1 pdi p0 pdg 0 0 0 0 1 0 0 modulator ref. bias current source internal temp. analog GND oscillator amplifier NOTE 1),3) 2) Notes: 1) This register defines the power-down signals of the building blocks 2) Default power-up state before any setting 3) The logic is positive (pdosc=1 means the corresponding block is in power-down) 7.5.3 CRA measurement channel A configuration register ( 17 bits ) Nr. 0 1 Bits CRA bit names Defaults 2 subreg. 16 cu2 15 cu1 14 cu0 13 M5 12 M4 11 M3 10 M2 9 M1 8 g1 7 g0 6 f 5 r 0 0 0 0 0 0 0 1 1 1 1 0 0 OSF OSR MM CRU CRM GN 4 3 2 mm n3 n2 0 0 1 n1 0 n0 0 0 NOTE 1), 3) 2) CRN Notes: 1) This register defines the measurement channel A configuration 2) Default power-up state before any setting 3) Bit M1 is control signal of the multiplexer for current input (for example M1=1 means that corresponding switch is closed). Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 16 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet subregister CRU: calibration constant selection for voltage path ( 3 bits) in registers CRA,CRB Nr. 0 Calibration const. U CAU0 cu2 cu1 cu0 0 0 0 1 CAU1 0 0 1 2 CAU2 0 1 0 3 CAU3 0 1 1 4 CAU4 1 0 0 5 CAU5 1 0 1 6 1548 1 1 0 7 1548 1 1 1 NOTE subregister CRM: measurement path for registers CRA,CRB Nr. Bits CRA bit names Defaults 13 M5 12 M4 11 M3 10 M2 9 M1 0 0 0 0 1 measurement RSHH-RSHL 2 0 1 0 0 0 voltage bus 3 0 1 0 1 0 voltage bus, internal temperature 4 0 1 1 0 0 voltage bus, reference low=RSHL 5 1 0 0 0 0 voltage bus, gain=1 6 1 0 0 1 0 voltage bus,gain=1, internal temperature 7 1 0 1 0 0 voltage bus, gain=1, reference low=RSHL 1 NOTE 1), 2) Notes: 1) these bits define the inner part of the voltage path settings 2) only the listed combinations are allowed subregister GN: gain definition bits, Registers CRA,CRB Nr. 0 GAIN 6 g1 0 g0 0 1 24 0 1 2 50 1 0 3 100 1 1 NOTE subregister OSF: oversampling frequency bit, Registers CRA,CRB Nr. 0 Fovs (fclk=8MHz) 2.048MHz Fovs (internal osc) 132kHz f 0 1 4.096MHz 264kHz 1 NOTE 1) 1) Notes: 1) For internal oscillator typical values subregister OSR: oversampling ratio bit, Registers CRA, CRB Nr. 0 R1 64 r 0 1 128 1 Revision 1.1, 04-April-06 NOTE www.austriamicrosystems.com Page 17 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet subregister MM: chopping ratio bit, Registers CRA, CRB Nr. 0 MM 4 mm 0 1 8 1 2 1 x NOTE 1) Notes: 1) For c=0 and d=0 , chopping and dechopping is switched off and every cycle is active regardless of mm, i.e. the sampling frequenzy is higher by a factor of 4 subregister CRN: averaging bits ( 4 bits), registers CRA,CRB Nr. 0 R2 1 n3 0 n2 0 n1 0 n0 0 NOTE 1 2 0 0 0 1 2 4 0 0 1 0 3 8 0 0 1 1 4 16 0 1 0 0 5 32 0 1 0 1 6 64 0 1 1 0 7 128 0 1 1 1 8 256 1 0 0 0 9 512 1 0 0 1 10 1024 1 0 1 0 11-14 Reserved for test 1 x x x 1) 15 raw mode 1 1 1 1 2) Note: 1) combinations from B to E are reserved for test 2) this mode delivers the AD-values without calibration and averaging but multiplied by a factor which is dependent on the setting of the oversampling ratio. It can be used for high resolution measurements of very low signals since it eliminates the internal rounding error. The ratio between raw result (Nr) and normal result (Nn) is given by: Nr/Nn = 2^(11+x)/CAL where x=6 for R=128 and x=3 for R=64. CAL is the calibration constant used. 7.5.4 Nr. 0 CRB measurement channel B configuration register ( 17 bits ) 1 Bits CRB bit names Defaults 2 subreg. 16 cu2 15 cu1 14 cu0 13 M5 12 M4 11 M3 10 M2 9 M1 8 g1 7 g0 6 f 5 r 4 mm 3 n3 2 n2 1 n1 0 n0 0 0 0 0 1 1 0 0 0 1 1 0 0 0 0 0 0 OSF OSR MM CRU CRM GN NOTE 1), 3) 2) CRN Notes: 1) This register defines the measurement channel B configuration, the functions of the subregisters are the same as described above for measurement channel A 2) Default power-up state before any setting 3) In this mode the chip cannot measure the current sensing input RSHH-RSHL, therefore M1=0 for all settings Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 18 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 7.5.5 ZZR Zener-Zap register (188 bits ): For the AS8500 the zener zap registers are set to a predefined default value. As an exception the TRIMA bits in the ZTR subregister is factory adjusted for minimum amplifier offset to ensure optimum linearity over input range. Nr. 0 ZZR bits 183-187 ZLO 163-182 ZTR 53-162 ZCL 0-52 ZTC1) NOTE 2) Notes: 1) 5 bits are reserved for: - 1 bit eventually destroyed during testing, - 2 bits for testing programmed 0 and 1 - 2 bits reserved for locking 2) due to a limited driving capability of the ZZR-cells the maximum reading speed is limited to 500 kHz subregister ZLO: Zener spare bits ( 5 bits ) Nr. 1 Name Reserved bits SYMBOL ZLO WORD WIDTH 5 Default Hex F subregister ZTR: trimming bits (20 bits) Nr. 0 TC of reference TRIMBTC WORD WIDTH 5 1 absolute value of reference TRIMBV 5 Bits 2 amplifier offset TRIMA 5 Bits 3 current source for external temperature ∑ trim bits TRIMC 5 Bits TRIMREG 20 Bits 4 PARAMETER SYMBOL UNIT Bits subregister ZCL: calibration bits ( 110 bits ) Nr. 0 Calibration G=6, I CGI1 WORD WIDTH 11 1 Calibration G=24, I CGI2 11 Bits 2 Calibration G=50, I CGI3 11 Bits 3 Calibration G=100, I CGI4 11 Bits 4 Calibration U0 CAU0 11 Bits 5 Calibration U1 CAU1 11 Bits 6 Calibration U2 CAU2 11 Bits Calibration U3 CAU3 11 Bits 8 Calibration U4 CAU4 11 Bits 9 Calibration U5 CAU5 11 Bits 10 ∑ cal. Bits ZCL 110 Bits 7 PARAMETER SYMBOL UNIT Bits Calibration constants are selected dependent on state of M1 ( see table below). For M1=1 one of CGI1 to CGI4 is selected according to selected gain of amplifier. For M1=0 the selection of the calibration constants is defined by bits (cu2,cu1,cu0), which are part of CRA and CRB registers and are defined via SDI interface independently of any other selection. Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 19 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet Calibration constant selection truth table Nr. cu2 cu1 cu0 M1 g1 x x x 1 0 0 g0 0 CAL CONST CGI1 1) NOTE 1 x x x 1 0 1 CGI2 1) 2 x x x 1 1 0 CGI3 1) 3 x x x 1 1 1 CGI4 1) 4 0 0 0 0 x x CAU0 2) 5 0 0 1 0 x x CAU1 2) 6 0 1 0 0 x x CAU2 2) 7 0 1 1 0 x x CAU3 2) 8 1 0 0 0 x x CAU4 2) 9 1 0 1 0 x x CAU5 2) 10 1 1 0 0 x x 1548 11 1 1 1 0 x x 1548 Notes: 1) CGIx calibration constants are selected when M1=1 according to selected gain 2) CGUx calibration constants are selected when M1=0 according to bits cu2 to cu0 defined via SDI in CRA and/or CRB registers. subregister ZTC: These bits are spare bits and can be used on special request (e.g. ID number). Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 20 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 7.5.6 CAR calibration register ( 110 bits ) The aim of the calibration register is to hold the calibration constants that are used by the internal DSP for the correction of each measurement (for the factory calibrated version AS8501). At power-up sequence the Zener-Zap subregister ZCL default setting is copied into the CAR register. The register can be read or written in mode 8 via the SDI bus at any time. In particular for the AS8500, which is not factory calibrated it is intended to overwrite the default setting with external data defined by the user. Nr. 0 1 CAR bits 109-99 98-88 Subregister CGI1 CGI2 default 1548 87-77 CGI3 76-66 CGI4 65-55 CAU0 54-44 CAU1 43-33 CAU2 32-22 CAU3 21-11 CAU4 10-0 CAU5 1548 0 1548 2047 2047 1548 1548 1548 1548 NOTE 1) 2) Notes: 1) Calibration register is composed of the following constants each having 11 bits: CGI1, CGI2, CGI3, CGI4, CAU0, CAU1, CAU2, CAU3, CAU4, CAU5 2) Decimal default value of the calibration constant for voltage and current is calculated using formula: CGdef=Nmax/NADdef=(Vref*1024)/(Vin*Gmax)=1548 7.5.7 TRR trimming register ( 20 bits ) In the TRR register the calibration constants for the reference voltage, for the amplifier-offset trim and for the current source setting are stored. At power-up sequence the Zener-Zap subregister ZTR is loaded into the TRR register. This register can be read or written in mode 8 via the SDI bus. In particular it is possible to write preliminary calibration constants into TRR or overwrite the loaded ZTR data, if a calibration has been changed. The trimming of the TRR-registors is usually done at the factory before supplying the part. Nr. 0 TRR bits Subregister 19-15 TRIMC 14-10 TRIMA 9-5 TRIMBV 4-0 TRIMBTC 1 default 4 typ 0 or 1 16 17 NOTE 1) Notes: 1)writing into TRR register is done as usual with the MSB first subregister TRIMC change of current source output with TRIMC bits Nr. trimcs trimc3 trimc2 trimc1 trimc0 dI/Io % Notes 0 0 0 0 0 0 0 1),2) 1 0 0 0 0 1 -1*2.3 1),2) 2 0 0 0 1 0 -2*2.3 1),2) .. .. .. .. .. .. .. 14 0 1 1 1 0 –14*2.3 1),2) 15 0 1 1 1 1 –15*2.3 1),2) 16 17 1 1 0 0 0 0 0 0 0 1 16*2.3 15*2.3 1),2) 18 1 0 0 1 0 14*2.3 1),2) .. .. .. .. .. .. .. 30 1 1 1 1 0 2*2.3 31 1 1 1 1 1 1*2.3 1),2) Notes: 1) Io is the current in µA at TRIMC = 00000 2) The output current of the internal current source can be controlled in a wide range via the bit setting in CRG. In some applications it may be necessary to trim the current in the rang of +/- 30% for an optimum result of the external temperature measurement. This trimming is achieved with writing into subregister TRIMC of the TRR register. The trimming is done in % for all ranges selected in CRG register. Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 21 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet subregister TRIMA The offset of the PGA is factory trimmed to a mimimum absolute value to guarantee the full dynamic range with all gain settings. change of amplifier offset with TRIMA bits Nr. trimas trima3 trima2 trima1 trima0 Voffset mV Notes 0 0 0 0 0 0 Uos 1),2) ,3) 1 0 0 0 0 1 Uos -1*1.34 1),2) 2 0 0 0 1 0 Uos -2*1.34 1),2) .. .. .. .. .. .. .. 14 0 1 1 1 0 Uos –14*1.34 1),2) 15 0 1 1 1 1 Uos –15*1.34 1),2) 16 17 1 1 0 0 0 0 0 0 0 1 Uos Uos +1*1.34 1),2) 18 1 0 0 1 0 Uos +2*1.34 1),2) .. .. .. .. .. .. .. 30 1 1 1 1 0 Uos +14*1.34 31 1 1 1 1 1 Uos +15*1.34 1),2) Notes: 1) Uos is the input offset voltage in mV at TRIMA = 00000 2) Every step of TRIMA settings brings Δoffset=1.34 mV change in absolute value of the input offset voltage. If the measured value is Uos then the number that should be written into the TRIMA for minimum final absolute value is calculated as TRIMA=int((Uos)/1.34) for Uos above zero and TRIMA=16+int(-Uos)/1.34) for Uos below zero. 3) The input offset voltage can be measured with chopping and dechopping bits being cleared in register CRG. Any input channel as well as gain settings can be used. The input should be shorted to avoid any external voltages to interfere with the measurement. If the measured output voltage is Va then the offset voltage is calculated acc. Vos = Va/gain. subregister TRIMBV change of reference voltage Uo with TRIMBV bits Nr. trimbvs trimbv3 trimbv2 trimbv1 trimbv0 VREF mV Notes 0 0 0 0 0 0 Ua 1),2) 1 0 0 0 0 1 Ua -1*5.1 1),2) 2 0 0 0 1 0 Ua -2*5.1 1),2) .. .. .. .. .. .. .. 14 0 1 1 1 0 Ua –14*5.1 1),2) 15 0 1 1 1 1 Ua –15*5.1 1),2) 16 17 1 1 0 0 0 0 0 0 0 1 Ua Ua +1*5.1 1),2) 18 1 0 0 1 0 Ua +2*5.1 1),2) .. .. .. .. .. .. .. 30 1 1 1 1 0 Ua +14*5.1 31 1 1 1 1 1 Ua +15*5.1 1),2) Notes: 1) Ua is the reference voltage in mV at TRIMBTC = 00000, the optimum value is 1.232V. 2) Every step of TRIMBV settings brings ΔBV=5.1 mV change in absolute value of the reference voltage. For trimming the TC value and absolute value of the reference voltage it is recommended to trim the TC value first and then trim the absolute value since TRIMBTC is changing both TC and absolute value, whereas TRIMBV is changing only the absolute value. If the measured absolute value is Uam then the number that should be written into the TRIMBV for optimum final absolute value is calculated as TRIMBV=int((Uam-1.231)/0.0051) for Uam above the ideal value and TRIMBV=16+int(-(Uam-1.232)/0.0051) for Uam below the ideal value. Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 22 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet subregister TRIMBTC change of reference voltage Uo and TC-value with TRIMBTC bits Nr. trimbtcs trimbtc3 trimbtc2 1 trimbtc1 1 trimbtc0 VREF mV TC ppm/K Notes 0 0 0 0 0 0 Uo TCo 1),2) 1 0 0 0 0 1 Uo -1*5.2 TCo -1*12.7 1),2) 2 0 0 0 1 0 Uo -2*5.2 TCo -2*12.7 1),2) .. .. .. .. .. .. .. 14 0 1 1 1 0 Uo –14*5.2 TCo -14*12.7 1),2) 15 0 1 1 1 1 Uo –15*5.2 TCo -15*12.7 1),2) 16 17 1 1 0 0 0 0 0 0 0 1 Uo Uo +1*5.2 TCo +1*12.7 18 1 0 0 1 0 Uo +2*5.2 TCo -2*12.7 .. .. .. .. .. .. .. .. 30 1 1 1 1 0 Uo +14*5.2 TCo -14*12.7 31 1 1 1 1 1 Uo +15*5.2 TCo -15*12.7 1),2) 1),2) 1),2) Notes: 1) Uo is the reference voltage in mV and TCo is the TC value in ppm/K at TRIMBV = 00000 2) Every step of TRIMBTC settings brings ΔBTC=5.2 mV change in absolute value of the reference voltage and S=12.7 ppm/K change in the slope of temperature dependence. So for trimming the temperature coefficient of the band-gap reference 2 measurements are recommended ( at T1=25oC and at T2=125oC ). If the measured TC value is TCm then the number that should be written into the TRIMBTC for minimum final TC is calculated as trimBTC=int(TCM/12.7) for positive values and trimBTC=16+int(-TCM/12.7) for negative values. The absolute voltage is also changed in this way, which must be compensated by bringing back the absolute value by changing the TRIMBV register. Usually the TRIMBVx=-TRIMBTCx+1 is sufficient. If further accuracy or change of absolute value is necessary it can be adjusted by making some more measurements and adjustments. ZZR REGISTER: ZLO ZTR ZCL ZTC 5 20 110 53 R/W TRR CAR reg.7 reg.6 bit0 data in bit0 CAR bit0 188 TRR ZLO bit0 Figure 4 Copying of ZCL and ZTR registers into CAR and TRR registers Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 23 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 7.5.8 THR alarm (Wake-up) threshold register ( 17 bits ) Nr. MR16 MR15 MR14 0 A/B s Msb default 0 0 1 MR13 MR12 MR11 … MR1 MR0 NOTE lsb 0 0 0 1) Notes: 1) _ All measurements are performed in channel A therefore MR16 must be set to zero. When channel B is selected no interrupt will be generated. - The signed value is used. For positive THR values the ASIC will initiate an interrupt whenever the measured value is bigger than the THR value. For negtive THR values the interrupt will be generated for a negative result with an absolute value bigger than the absolute value of the THR register. 7.5.9 MSR measurement result register ( 18 bits ) Nr. MR17 MR16 MR15 MR14 Overflow/un derflow A/B S msb MR13 MR12 MR11 … MR1 MR0 lsb NOTE 1) Notes: 1) - Result word length is 16 bits because of calibration accuracy and to maintain all possible resolutions ( different setting ). - A/B bit signifies which measurement was performed: the one defined in CRA or CRB: MR16=0 -> A MR16=1 -> B - Overflow/underflow bit is set whenever the result after multiplication by calibration constant is bigger than 32767 or smaller than –32767. In Wake-up or Alarm mode the overflow/underflow always sets INTN signal to LO. 8 Digital interface description The digital interface of the AS8501 consists of two input pins (CLK and SCLK) and two I/O pins (INTN and SDAT). The SCLK and SDAT pins are used as universal serial data interface (SDI). SDI operates only if external clock signal (CLK) is running. 8.1 CLK In all operating modes except the Wake-up mode this pin must be connected to 8 MHz clock signal. In the Wake-up mode (MWU) the CLK pin must be connected to logic HI or float. 8.2 INTN The INTN pin is used to signal various conditions to the microcontroller, depending on the operating mode. application modes of the INTN pin Mode 0 Signal Load clock (internal) Direction Output Purpose Indicates progress of the Zener-Zap load process 1, 2,7 SDI clock disable Output 3 idle / wake-up not Output Signals new result and suggests when to disable SCLK in high-precision measurement phase Signals the wake-up condition 4 idle / alarm not Output Signals the alarm condition 5 PW1 Input Shows the programming pulse width Logic ‘0’ Output No purpose 10 t12 Output Test mode 10 t18 Output Test mode 6,8,9 Note 1) 2) Notes: 1) 188 clock pulses are generated from the internal oscillator source during the loading time. 2) In measurement modes (MMS and MMD) the INTN pin is used to synchronize the SDI bus operations (see figure 5). The trailing edge of INTN signals the start of a new measurement. Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 24 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet i-1 start measurement i i+1 Tcnv INTN available results on SDI i-2 i-1 i Tres Figure 5: INTN pin in modes 1 and 2 The determination of Tcnv and Tres from the parameter settings is: Tcnv ≅ R1/(fovs*2) 8.3 Tres = MM*Tcnv*R2*2 with R1=OSR and R2=number of averages SDI bus operation SDI bus is a 2-line bi-directional interface between one master and one slave unit. Typically the master unit is a microcontroller with softwareimplemented SDI protocol. The ASIC is always the slave unit. SDI bus operation is presented on figure 6. During data transfers the sdat signal changes while sclk is low. The sdat signal can change while sclk is high only to generate start or exception conditions. Direction Address Register data sclk SDAT Start Figure 6: SDI bus operation Data transfer Exception Strobe ASIC The master unit always generates the sclk signal. The master unit generates the sdat signal in start, direction, address, master-write data and exception conditions. The master sdat pin is in high-impedance state in master-read data condition. Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 25 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet The slave unit drives the sdat signal only in master-read data condition. In all other cases the slave sdat pin is in high-impedance state. During data transfer in read condition the internal AD-conversion in continuing but the data in the MSR-register is not updated and the output of the INTN signal is suppressed. Only after the completion of the reading cycle the ASIC returns to the normal condition and updates the MSRregister immediately if a new AD-conversion has been finished during data transfer. The master unit does not detect any bus conditions since it generates them. Data transfer conditions (direction, register address and register data) must not be changed until the current condition is over. The slave unit does not detect start and exception condition when master-read is in progress. The exception condition is reserved for future use and should be avoided. 8.4 Data transfers Generally the SDI interface is active in all ASIC modes. For security reasons some write operations are restricted to certain modes. Read operations are never disabled in order to keep consistent sdat driving conditions. Writing to the result, trimming and calibration registers (MSR, CAR and TRR) is allowed only in test modes. Writing to the Zener-Zap register is allowed only in mode MZP. The first data bit after the start condition in each data transfer defines the data direction: sdat=high is used for master-read data (mr) condition and sdat=low for master-write data (mw) condition. Data is transferred with the most significant bit (MSB) first. Data bits are composed of register address and register data bits. Register address is transmitted first, followed by the register data bits. The register address is always 4 bits long. The number of register data bits (see 7.5) is implied by the register address. sclk mr sdat a3 a2 a1 a0 MSB LSB mw Direction Register address Register data Figure 7: SDI Data transfer The ASIC supports the data transfers presented in the following table: master read-write operations REGISTER ADDRESS OPM 0 operating mode CRA 1 measurement set-up A All All CRB 2 measurement set-up B All All CRG 3 general measurement conditions All All MSR 4 measurement result All >7 ZZR 5 Zener-Zap data All 5 CAR 6 calibration register All >7 TRR 7 trimming register All >7 THR 8 alarm or wake-up threshold register All All Revision 1.1, 04-April-06 Contents read write allowed in allowed in modes modes All All www.austriamicrosystems.com page Page 26 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 8.5 SDI bus timing Timing definitions for SDI bus are based on software-implemented master unit protocol MDE DV_m PW_sclk DV_m TS_m TS_m LO_sclk sclk (uP) master sdat HI - Z (uP) slave sdat HI - Z (ASIC) TS_s DV_s TS_S CDD strobe ASIC strobe µC Figure 8: SDI Bus timing Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 27 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet SDI bus timing Nr. PARAMETER SYMBOL MIN 0 SCLK pulse width PW_sclk 1 SCLK low LO_sclk 2 5 Master SDAT exception after SCLK Master SDAT valid before/after SCLK Slave SDAT not valid after SCLK Master 3-state ON/OFF 6 Slave 3-state ON/OFF TS_s Bus condition detection disabled in slave unit CDD 3 4 7 TYP Unit Conditions 120 ns All 120 ns All MDE 120 ns All DV_m 120 ns All ns Master read ns Master read ns Master read ns Master read TSW DV_s TS_m MAX 120 TS_s TSW 120 NOTE 5), 6) 1) 3) Notes: 1)TSW is typical time required by the microcontroller program to change or to read the state of the I/O pin 3) Start detection is disabled when slave unit transmits data 5) LO_sclk>300ns and PW_sclk> 2µsec required to read ZZR. 6) LO_sclk > (3/2)*TCLK = (3/2)/f CLK = (3/2)/8MHz=187.5ns required for results synchronisation in MSR. 8.6 SDI access to OTP memory SDI can read the OTP memory in any mode by reading the register ZZR. 8.6.1 ZZR register bit mapping Cell index Purpose 0 pos A 1) 1 pos B 2) 2 pos C 3) ZZR field ZLO ZLO ZLO ZZR bit 187 (msb) 186 185 3 lock A 4 lock B 5) 5 trimcs 6 trimc3 7 trimc2 ZLO ZLO ZTR ZTR ZTR 184 183 182 181 180 4) 1) Always programmed to '0' during the production test programmed to '0' during the production test 3) Always programmed to '1' during the production test 4) Reserved 5) Reserved 2) Always Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 28 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet Cell index Purpose 8 trimc1 9 trimc0 10 trimas 11 trima3 12 trima2 13 trima1 14 trima0 15 trimbvs ZZR field ZTR ZTR ZTR ZTR ZTR ZTR ZTR ZTR ZZR bit 179 178 177 176 175 174 173 172 Cell index Purpose 16 trimbv3 17 trimbv2 18 trimbv1 19 trimbv0 20 trimbtcs 21 trimbtc3 22 trimbtc2 23 trimbtc1 ZZR field ZTR ZTR ZTR ZTR ZTR ZTR ZTR ZTR ZZR bit 171 170 169 168 167 166 165 164 Cell index Purpose 24 trimbtc0 25 cgi1_10 26 cgi1_9 27 cgi1_8 28 cgi1_7 29 cgi1_6 30 cgi1_5 31 cgi1_4 ZZR field ZTR ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZZR bit 163 162 161 160 159 158 157 156 Cell index Purpose 32 cgi1_3 33 cgi1_2 34 cgi1_1 35 cgi1_0 36 cgi2_10 37 cgi2_9 38 cgi2_8 39 cgi2_7 ZZR field ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZZR bit 155 154 153 152 151 150 149 148 Cell index Purpose 40 cgi2_6 41 cgi2_5 42 cgi2_4 43 cgi2_3 44 cgi2_2 45 cgi2_1 46 cgi2_0 47 cgi3_10 ZZR field ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZZR bit 147 146 145 144 143 142 141 140 Cell index Purpose 48 cgi3_9 49 cgi3_8 50 cgi3_7 51 cgi3_6 52 cgi3_5 53 cgi3_4 54 cgi3_3 55 cgi3_2 ZZR field ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZZR bit 139 138 137 136 135 134 133 132 Cell index Purpose 56 cgi3_1 57 cgi3_0 58 cgi4_10 59 cgi4_9 60 cgi4_8 61 cgi4_7 62 cgi4_6 63 cgi4_5 ZZR field ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZZR bit 131 130 129 128 127 126 125 124 Cell index Purpose 64 cgi4_4 65 cgi4_3 66 cgi4_2 67 cgi4_1 68 cgi4_0 69 cau0_10 70 cau0_9 71 cau0_8 ZZR field ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZZR bit 123 122 121 120 119 118 117 116 Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 29 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet Cell index Purpose 72 cau0_7 ZZR field cau0_6 74 cau0_5 75 cau0_4 76 cau0_3 77 cau0_2 78 cau0_1 79 cau0_0 ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZZR bit 115 114 113 112 111 110 109 108 Cell index Purpose ZZR field 80 cau1_10 ZCL 81 cau1_9 ZCL 82 cau1_8 ZCL 83 cau1_7 ZCL 84 cau1_6 ZCL 85 cau1_5 ZCL 86 cau1_4 ZCL 87 cau1_3 ZCL ZZR bit 107 106 105 104 103 102 101 100 Cell index Purpose 88 cau1_2 89 cau1_1 90 cau1_0 91 cau2_10 92 cau2_9 93 cau2_8 94 cau2_7 95 cau2_6 ZZR field ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZZR bit 99 98 97 96 95 94 93 92 Cell index Purpose 96 cau2_5 97 cau2_4 98 cau2_3 99 cau2_2 100 cau2_1 101 cau2_0 102 cau3_10 103 cau3_9 ZZR field ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZZR bit 91 90 89 88 87 86 85 84 Cell index Purpose 104 cau3_8 105 cau3_7 106 cau3_6 107 cau3_5 108 cau3_4 109 cau3_3 110 cau3_2 111 cau3_1 ZZR field ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZZR bit 83 82 81 80 79 78 77 76 Cell index Purpose 112 cau3_0 113 cau4_10 114 cau4_9 115 cau4_8 116 cau4_7 117 cau4_6 118 cau4_5 119 cau4_4 ZZR field ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZZR bit 75 74 73 72 71 70 69 68 Cell index Purpose 120 cau4_3 121 cau4_2 122 cau4_1 123 cau4_0 124 cau5_10 125 cau5_9 126 cau5_8 127 cau5_7 ZZR field ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZZR bit 67 66 65 64 63 62 61 60 Cell index Purpose 128 cau5_6 129 cau5_5 130 cau5_4 131 cau5_3 132 cau5_2 133 cau5_1 134 cau5_0 135 tcu1_8 ZZR field ZCL ZCL ZCL ZCL ZCL ZCL ZCL ZTC ZZR bit 59 58 57 56 55 54 53 52 Revision 1.1, 04-April-06 73 www.austriamicrosystems.com Page 30 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet Cell index Purpose 136 tcu1_7 ZZR field tcu1_6 138 tcu1_5 139 tcu1_4 140 tcu1_3 141 tcu1_2 142 tcu1_1 143 tcu1_0 ZTC ZTC ZTC ZTC ZTC ZTC ZTC ZTC ZZR bit 51 50 49 48 47 46 45 44 Cell index Purpose 144 tcu0_8 145 tcu0_7 146 tcu0_6 147 tcu0_5 148 tcu0_4 149 tcu0_3 150 tcu0_2 151 tcu0_1 ZZR field ZTC ZTC ZTC ZTC ZTC ZTC ZTC ZTC ZZR bit 43 42 41 40 39 38 37 36 Cell index Purpose 152 tcu0_0 153 trt0_10 154 trt0_9 155 trt0_8 156 trt0_7 157 trt0_6 158 trt0_5 159 trt0_4 ZZR field ZTC ZTC ZTC ZTC ZTC ZTC ZTC ZTC ZZR bit 35 34 33 32 31 30 29 28 Cell index Purpose 160 trt0_3 161 trt0_2 162 trt0_1 163 trt0_0 164 tcn3_7 165 tcn3_6 166 tcn3_5 167 tcn3_4 ZZR field ZTC ZTC ZTC ZTC ZTC ZTC ZTC ZTC ZZR bit 27 26 25 24 23 22 21 20 Cell index Purpose 168 tcn3_3 169 tcn3_2 170 tcn3_1 171 tcn3_0 172 tcn2_7 173 tcn2_6 174 tcn2_5 175 tcn2_4 ZZR field ZTC ZTC ZTC ZTC ZTC ZTC ZTC ZTC ZZR bit 19 18 17 16 15 14 13 12 Cell index Purpose 176 tcn2_3 177 tcn2_2 178 tcn2_1 179 tcn2_0 180 tcn1_7 181 tcn1_6 182 tcn1_5 183 tcn1_4 ZZR field ZTC ZTC ZTC ZTC ZTC ZTC ZTC ZTC ZZR bit 11 10 9 8 7 6 5 4 Cell index Purpose 184 tcn1_3 185 tcn1_2 186 tcn1_1 187 tcn1_0 ZZR field ZTC ZTC ZTC ZTC 3 2 1 0 ZZR bit Revision 1.1, 04-April-06 137 www.austriamicrosystems.com Page 31 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 8.6.2 ZZR ZLO ZTR ZCL Stored ZZR-register mapping subreg TRIMC TRIMA TRIMBV TRIMBTC CGI1 CGI2 CGI3 CGI4 CAU0 CAU1 CAU2 CAU3 CAU4 CAU5 bitno in subregister 10 9 8 7 6 msb 1 1 1 0 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 ZTC Revision 1.1, 04-April-06 0 0 0 0 0 1 1 0 0 0 1 1 1 0 0 0 0 0 1 1 0 0 0 1 1 1 1 1 1 0 0 0 0 0 1 1 0 0 0 1 1 1 1 1 1 ZZR bits 5 4 3 2 1 0 0 0 0 0 1 1 0 0 0 1 1 1 1 1 1 x 0 x 1 1 0 0 0 0 0 1 1 0 0 0 1 1 1 1 1 1 x 0 x 0 0 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 x 1 x 0 0 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 x 0 x 0 0 0 0 0 0 0 1 1 0 0 0 1 1 1 1 1 1 0 lsb x 0 x 0 1 0 0 0 0 0 1 1 0 0 0 1 1 1 1 1 1 187 182 177 172 167 162 151 140 129 118 107 96 85 74 63 52 43 34 23 15 7 www.austriamicrosystems.com Remarks 183 178 173 168 163 152 141 130 119 108 97 86 75 64 53 44 35 24 16 8 0 current souce PGA offset voltage reference reference TC gain 6 current gain 24 current gain 50 current gain 100 current gain 24 gain 1 gain 100 inernal temperature spare bits Page 32 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 9 General application hints Since the AS8501 is optimised for low voltage applications extreme care should be taken that the signal is not disturbed by influences like bad ground reference, external noise pick-up, thermal EMFs generated at the transition of different materials or ground loops. The influence of these error sources can be quite high and they may completely shadow the excellent properties of the device if not handled properly. The following sections are supposed to supply additional informations to the design engineer how to get around some of these problems. 9.1 Ground connection, analog common The analog common terminal where all voltages are referring to is RSHL. All ground lines of the external circuitry of VBAT, ETS and ETR as well as the voltage sense line of the low ohmic current sensing resistor should be connected to each other in a star like ground point. It is recommended that this point is as close as possible situated to the low side sense terminal of the current sensing resistor. It should also be connected to the VSS and VSSD terminal, but the return line of both must leave this point separately. Also the power decoupling capacitors should be connected to the analog common. To give an example of the magnitude of possible errors consider that the ground return of the power supply is not connected properly and 5 mm of a copper track 35µm thick and 0.1 mm wide are within the measuring circuit with a current flow of 5 mA. This will result in an offset of 120 µV which is more than 500 times higher than the typical offset of the ASIC. In addition the current fluctuations will act as an extra noise voltage which is also way above that of the device itself. 9.2 Thermal EMF another major source of error for low level measurements are thermal voltages (electromotive force, thermal EMF) or Seebeck voltages which are principally produced by any junction of two dissimilar materials. On PC-boards pairs of dissimilar materials may consist of the copper tracks and the solder, the leads of different components or different materials used in the construction within the components. Any temperature difference between two connection produces a voltage which is superimposed to the measuring voltage. A number of strategies are known to detect or minimise their influence on the measuring result: - - - in cases were a current has to be measured directly or a current is to be used to activate a resistive sensor (like Ohm-meter or temperature measurement with RTDs, NTC or PTC) a switch in the circuit could be used to interrupt or invert the current thus producing a current change dI. In the difference of the two voltage states dU the EMFs as well as the Offset voltages of the amplifier are fully eliminated. For resistance measurements this method is known as ‘true Ohm’ measurement. in applications were this is not possible and the problematic device (i.e. the input resistor of an amplifier) can be located it may help to place a dummy device of the same type in the circuit as close and thermally connected as good as possible to compensate the influence of the first one. Since the thermal EMFs are proportional to the temperature difference it is important to maintain a homogeneous temperature distribution in the vicinity of the sensitive area. This is possible by keeping this area as small as possible, by avoiding any heat sources nearby or by increasing the heat conductivity of the substrate, i.e. wide and thick copper tracks, multilayer board or even metal substrate. The best solution of all however is to avoid the thermal EMFs by using only components which are matched to the copper world which means that their thermo-electrical power against copper is zero. This is specially important for current measurements in the range of 10- 1000A. In this case the resistance value has to be very low (down to 100µOhms) to limit the measuring power and avoid an overheating of the sensing resistor. On the other hand the voltages to be detected are extremely low if a high resolution is required. If for instance a current of 10 mA has to be measured with a 100µOhm resistor, the resolution of the measuring system must be better than 1µV and the error voltages due to thermal EMFs must be below this limit. Quite often people are trying to use the well known Konstantan (CuNi44) for current sensing resistors. This is a bad choice since the thermal EMF versus copper is very high. With –40µV/deg already a temperature difference of 2.5 K is enough to produce an error which is 100 times lager than the required resolution. Or vice versa a temperature fluctuation of only 1/100 K produces a ‘thermal noise’ which is equivalent to the required resolution. With such materials and high currents of 10A and above the other thermoelectric effect, the so called Peltier-effect, can also play an important role. Under current flow this effect generates heat in one junction and destroys the same amount of heat in the other junction. The amount of heat is proportional to the current and its direction. The result is a temperature difference which in turn generates a thermal EMF proportional to it. Finally this means that such a resistor produces its own error voltage and it is never possible to measure better than 1-2% with such badly matched materials. The precision resistance materials Manganin, Zeranin and Isaohm are perfectly matched to the copper world and resistors made from these materials can achieve the high quality that is necessary for low level measurements and high resolution. 9.3 Noise considerations for every low level measuring system it is essential to know the origin of noise and to accept the limitations given by it. Three major sources of noise have to be considered. The input voltage noise and the input current noise of the amplifier and the thermal noise (Johnson noise) of resistors in the external circuitry around the amplifier. Due to the fact that these three sources are not correlated they can be added in the well known square root equation. In most applications the input resistor or input divider is low ohmic (i.e. below 10 kOhms) which mean that the noise voltage produced by the input current noise is negligible compared to the input voltage noise. The input noise density (En) of the AS8501 is with only 35 nV/sqr(Hz) extremely low. This could be achieved with a special internal analog and digital chopper circuitry which eliminates the CMOS typical 1/f-noise completely. Even though the overall noise will be dominated by the input amplifier as long as the external resistors are below 10 kOhm. The total noise voltage generated at a given frequency resp. in a given frequency band (BW) is given by: Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 33 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet Un= En*sqr(BW) This square root dependence can be seen very nicely in fig. 9.10. The typical square-root shaped dependence is found for both the peak to peak noise as well as for the equivalent RMS noise. The bandwidth resp. the sampling frequency of the AS8501 can be adapted to the requirements of the application by programming the internal digital filter via the SDI bus. For a sampling frequency of 16kHz the input voltage RMS noise is less than 5µV, whereas at 500 Hz already 1µV (or 1LSB) is reached. If the customer needs even higher resolution at a lower measuring speed the internal integration time can be further increased but due to the limitation of the digital noise ( 1LSB) it is better to perform an external averaging in the attached µC. In this way the resolution of the system can be considerably increased to less than 0.1 µV for sampling rates of 5 Hz and below which corresponds to an effective AD-converter width of more than 20 bits. (see fig. 9.10) 9.4 Shielding, guarding In many applications it is difficult to gain full benefit from the AS8501 performance since a number of external error sources can disturb the measurement. To achieve the maximum performance the design engineer has to take care specially of the layout of the PC-board and the sense connections to the external components. To avoid noise pick-up from external magnetic fields all tracks on the PC-board should be parallel strip lines and they should be traced as close as possible to each other. External sensing cables should be twisted and kept away from current carrying cables as far as possible. For longer cables a shielding is sometimes helpful but care should be taken that the shield is not connected to one of the sense leads. For an optimum performance it should be open on one side, the other side should be connected to the central (star like) analog common point. In very sensitive applications it may be wise to use a guard ring around both inputs and it should be connected again to the analog common point. This procedure minimises leakage currents and parasitic capacitances between different terminals and components on the PC-board. EMV interferences can be affectively avoided in most cases by using standard SMD-type high frequency filters in the analog input lines as well as in the digital output lines. Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 34 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 10 Typical performance characteristics parameters: 300A, G24, AV4, OSF 2.048, OSR 128 parameters: 300A, G24, AV32, OSF 2.048, OSR 128 250 A 15 mA 0A -150 A -250 A linearity deviation in % output in digits 10 5 0 -5 -10 0 500 1000 1500 2000 0,5 0,3 0,0 -0,3 -0,5 -25,0 0,0 25,0 measurement no. 50,0 75,0 100,0 125,0 temperature in deg C Figure 13: Resolution and noise at zero input, sampling rate: 1kHz Figure 14: Linearity deviation for different currents over temperature parameters: 300A, G24, AV4, OSF 2.048, OSR 128 parameters: 300A, G24, AV4, OSF 2.048, OSR 128 0,03 output in digits linearity deviation in % 30010 0,02 0,01 0,00 -400 -300 -200 -100 0 100 200 300 400 -0,01 -0,02 30005 30000 29995 29990 0 -0,03 500 input current in A 2000 G24,AV=4,1000Hz, external averaging dual channel measurement, sampling rate f=8 RSHH-RSHL 100Hz square kHz VBAT 10 220Hz sine noise in digits or µV output / digits 1500 Figure 16: Resolution and noise at 95% full scale, sampling rate: 1kHz Figure 15: Linearity deviation over input signal 10000 1000 measurement no. 5000 0 -5000 p p 1 sigma 2.048 MHz 0,1 4.096 MHz 'best chopper OPA of the world' peak to peak 0,01 -10000 200 220 240 260 280 1 Figure 17: Dual mode measurement Revision 1.1, 04-April-06 10 100 1000 10000 final frequency in Hz measurement number Figure 18: Output voltage noise over sampling rate www.austriamicrosystems.com Page 35 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 5,0 2,0 1,5 1,0 2,5 change in % change in % 0,5 0,0 0,0 -0,5 -1,0 G6 -2,5 G24 G6 G24 G50 G100 -1,5 -2,0 -50 0 -25 25 50 75 100 -5,0 -50 125 0 -25 temperature deg C Figure 19: Typical output as function of temperature for gains 6 and 24 IHM-A-1500 IHM-A-1500 parameters: gain24, sampling rate 125 Hz 300A, G24, AV1, OSF 2.048, OSR 128 15 10 output in digits output in digits 75 5 0 -5 -10 -15 -20 2,5 5 7,5 10 100 125 Figure 20: Typical output as function of temperature for all gains 20 0 25 50 temperature deg C 2500 2000 1500 1000 500 0 -500 -1000 -1500 -2000 -2500 AC input frequency 100 Hz 0 time in sec 10 20 30 40 50 measurement no. Figure 22: Real time AC measurement at 100 Hz Figure 21: Noise at 125 Hz sampling rate, gain 24 IHM-A-1500 temperature dependence of reference voltage 0,4 change in % 0,2 0,0 original -0,2 -0,4 -40 -20 0 20 40 60 80 100 120 temperature in °C Figure 23: temperature dependence of internal reference voltage (not trimmed) Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 36 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 11 Package Dimensions Thermal Resistance junction / ambient.: 66 K/W (typ.) in still air 12 Revision History Revision 13 Date Description 1.0 Feb.10, 2006 Initial Revision 1.1 March 23, 2006 TRIMA 8.6.2, RthJA Ordering Information Delivery: Tape and Reel (1 reel = 1500 devices) = MOQ Order AS8501 Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 37 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet 14 14.1 Contact Headquarters austriamicrosystems AG A 8141 Schloss Premstätten, Austria Phone: +43 3136 500 0 Fax: +43 3136 525 01 [email protected] www.austriamicrosystems.com 14.2 Sales Offices austriamicrosystems Germany GmbH Tegernseer Landstrasse 85 D-81539 München, Germany Phone: +49 89 69 36 43 0 Fax: +49 89 69 36 43 66 austriamicrosystems Italy S.r.l. Via A. Volta, 18 I-20094 Corsico (MI), Italy Phone: +39 02 4586 4364 Fax: +39 02 4585 773 austriamicrosystems France S.A.R.L. 124, Avenue de Paris F-94300 Vincennes, France Phone: +33 1 43 74 00 90 Fax: +33 1 43 74 20 98 austriamicrosystems Switzerland AG Rietstrasse 4 CH 8640 Rapperswil, Switzerland Phone: +41 55 220 9008 Fax: +41 55 220 9001 austriamicrosystems UK, Ltd. 88, Barkham Ride, Finchampstead, Wokingham Berkshire RG40 4ET, United Kingdom Phone: +44 118 973 1797 Fax: +44 118 973 5117 austriamicrosystems AG Klaavuntie 9 G 55 FI 00910 Helsinki, Finland Phone: +358 9 72688 170 Fax: +358 9 72688 171 austriamicrosystems AG Bivägen 3B S 19163 Sollentuna, Sweden Phone: +46 8 6231 710 Revision 1.1, 04-April-06 austriamicrosystems USA, Inc. 8601 Six Forks Road Suite 400 Raleigh, NC 27615, USA Phone: +1 919 676 5292 Fax: +1 509 696 2713 austriamicrosystems USA, Inc. 4030 Moorpark Ave Suite 116 San Jose, CA 95117, USA Phone: +1 408 345 1790 Fax: +1 509 696 2713 austriamicrosystems AG Suite 811, Tsimshatsui Centre East Wing, 66 Mody Road Tsim Sha Tsui East, Kowloon, Hong Kong Phone: +852 2268 6899 Fax: +852 2268 6799 austriamicrosystems AG AIOS Gotanda Annex 5th Fl., 1-7-11, Higashi-Gotanda, Shinagawa-ku Tokyo 141-0022, Japan Phone: +81 3 5792 4975 Fax: +81 3 5792 4976 austriamicrosystems AG #805, Dong Kyung Bldg., 824-19, Yeok Sam Dong, Kang Nam Gu, Seoul Korea 135-080 Phone: +82 2 557 8776 Fax: +82 2 569 9823 austriamicrosystems AG Singapore Representative Office 83 Clemenceau Avenue, #02-01 UE Square 239920, Singapore Phone: +65 68 30 83 05 Fax: +65 62 34 31 20 www.austriamicrosystems.com Page 38 of 39 austriamicrosystems AS8500 - Preliminary Data Sheet Disclaimer Devices sold by austriamicrosystems AG are covered by the warranty and patent identification 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 life-sustaining equipment are specifically not recommended without additional processing by austriamicrosystems AG for each application. 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. No obligation or liability to recipient or any third party shall arise or flow out of austriamicrosystems AG rendering of technical or other services. Copyright Devices sold by austriamicrosystems are covered by the warranty and patent indemnification provisions appearing in its Term of Sale. austriamicrosystems 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 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 for current information. This product is intended for use in normal commercial applications. Copyright © 2004 austriamicrosystems. 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. To the best of its knowledge, austriamicrosystems asserts that the information contained in this publication is accurate and correct. However, austriamicrosystems 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. No obligation or liability to recipient or any third party shall arise or flow out of austriamicrosystems rendering of technical or other service Revision 1.1, 04-April-06 www.austriamicrosystems.com Page 39 of 39