MLX90320LFRLFR

MLX90320 Automotive small sensor interface Features and Benefits   Applications Examples   Ordering Information Part No. MLX90320LFR Temperature Code L (-40°C to 150°C) Package Code FR (SSOP 209 mil) 1 Functional diagram " #7 # $ * "" + * "" + 2 General description #$# % " &# + 7083 70 # + )0 )3 3 % 0$ $ $ ## => ? !( !) $ ! 09 : ( ; < = @; < + 1 ' The MLX90320 covers the most typical resistive type of Wheatstone bridge applications for use in an automotive environment. It is a monolithic silicon analog integrated sensor interface that converts small changes in resistors, configured in a full Wheatstone bridge on a sensing element, to large output voltage variations. The signal conditioning includes gain adjustment, offset control and second order temperature compensation in order to accommodate variations of the different resistive sensing elements. Compensation values are stored in EEPROM and can be reprogrammed with an interface circuit and a provided software. The MLX90320 is programmed with a single wire serial interface through the output pin. The user can specify on chip clamping levels thus creating fault detection bands. By intercepting various fault modes the MLX90320 is able to inform about the reliability of its analog output signal. () #$ , , -- ""#$ % & "& )0 +0 % % + % 1 () () () / / / / / 22)3 / / / / ( )4 / '5 ! / 6/ / ( / // ( )4 ()4 # % "4 / / + $/ #$/ '. 3901090320 Rev 004 Page 1 of 32             Suited cost optimized sensors: gain and offset correction by programmable coefficients Higher order temperature compensation provided for both gain and offset External or internal temperature sensor for compensation of temperature errors Over-voltage protection Fault detection and clamping levels Ratio-metric output: 0 to 5V Single Pin Digital Programming Fully analog signal path               Pressure transducers, strain gauges, accelerometers, position sensors, etc. Steering systems (e.g. torque sensors) Safety restraints systems (e.g. seat occupant detection) Braking systems (e.g. ABS, force) Comfort systems (e.g. air conditioning) Engine management (e.g. injection) Any bridge type sensor Data Sheet Mar/05 MLX90320 Automotive small sensor interface Table of Contents 1 Functional diagram ................................................................................................................ 1 2 General description................................................................................................................ 1 3 Maximum ratings.................................................................................................................... 3 4 Pad definitions and descriptions ............................................................................................ 4 5 MLX90320 General Specifications......................................................................................... 5 6 Detailed Description............................................................................................................... 9 6.1 EEPROM .......................................................................................................................... 10 6.2 The programmable clock. ................................................................................................. 10 6.3 The temperature chain...................................................................................................... 11 6.4 The sensor signal chain. ................................................................................................... 12 6.4.1 The Gain calibration of the sensor signal chain. ............................................................ 13 6.4.2 The Offset calibration of the sensor signal chain. .......................................................... 14 6.4.3 The output clamping levels ............................................................................................ 15 6.4.4 The Faults detection ...................................................................................................... 16 6.5 Programming the MLX90320 through the output pin ........................................................ 18 6.5.1 Overview........................................................................................................................ 18 6.5.2 Communication Request................................................................................................ 18 6.5.3 Bit format ....................................................................................................................... 19 6.5.4 Commands .................................................................................................................... 20 7 Unique Features .................................................................................................................. 22 8 Typical applications circuits ................................................................................................. 23 8.1 Ratio-metric mode with use of external temperature sensor............................................. 23 8.2 Ratio-metric mode without use of external temperature sensor........................................ 24 8.3 Non Ratio-metric mode with use of external temperature sensor. .................................... 24 8.4 Non Ratio-metric mode without use of external temperature sensor. ............................... 25 9 EEPROM Contents .............................................................................................................. 25 10 Reliability Information......................................................................................................... 29 11 ESD Precautions................................................................................................................ 29 12 Package Information .......................................................................................................... 30 13 Disclaimer .......................................................................................................................... 32 3901090320 Rev 004 Page 2 of 32 Data Sheet Mar/05 MLX90320 Automotive small sensor interface 3 Maximum ratings Parameter. Supply Voltage, VDD Supply Voltage, VDD- VSS Output current limit Operating Temperature Range, Tenvironment Storage Temperature Range Programming Temperature Range Package Thermal Resistance ESD Sensitivity Latch-up withstand Table 1: Absolute maximum ratings Exceeding the absolute maximum ratings may cause permanent damage. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. 2 Min -14 4.5 -50 9 -40 -50 -40 Max 16 5.5 -9 50 140 150 125 130 Units V V mA mA ºC °C °C °C/W kV HBM. CDF - AEC - Q100-002 CDF - AEC - Q100-004; VDD= 5.5V Comments No latch-up or damage. Rise time(10 to 90%) tr ≥ 1µ s. Operating within specifications Short to VDD Short to Gnd 3901090320 Rev 004 Page 3 of 32 Data Sheet Mar/05 MLX90320 Automotive small sensor interface 4 Pad definitions and descriptions Package Pin Short Nr Name 1 INM 2 3 4 5 6 7 8 9 10 11 12 13 14 ANAGND INP SUB TMP DIGGND Test TESTOU T TESTIN1 TESTIN2 FLT OUT Test VDD Dir IN gnd IN gnd IN gnd NC OUT IN IN OUT BI NC power Type Analog Analog Temp Function / Description Bridge Sensor Negative Analog Ground Bridge Sensor Positive Substrate Ground External Temperature Sensor (Resistor to supply) Digital Ground On module to ground. Test Test Test Analog Analog Supply Test Output. On module to ground Test Input 1: CLKEXT, TEST (3 level) Test Input 2: DATAIN, SCAN (3 level) Filter pin Analog output and communication pin On module to ground Supply Table 2: Pin description MLX90320 3901090320 Rev 004 Page 4 of 32 Data Sheet Mar/05 MLX90320 Automotive small sensor interface 5 MLX90320 General Specifications DC Operating Parameters TA = -40 C to 140 C, VDD = 5V (unless otherwise specified) General Electrical Specifications Comments Min Typ 4.5 No output load, VDD=5V±10% 10Ω < RSERIES < 10 kΩ 0 2 ± 2.5 VDD=5V±10% ±2 0 ±50 ±5 22 o o Parameter. Supply Voltage Supply Current Output capacitive load Output resistive load Output current capability Output short circuit current Digital output current VDD line inductance Symbol VDD IDD Max 5.5 7 300 Units V mA nF kΩ mA mA mA µH Parameter. Clamping output low 0 Clamping output low 1 Symbol Clamp low min Clamping Levels Specifications Comments Min Typ See paragraph 6.4.3 for detailed explanation 7 other low clamping levels with a clamp level variation of 1.3%VDD for each n = [0..7] 95 3 4 Max 5 Units %VDD Clamp low min + 1.3%VDD % VDD Clamping output low n Clamp low min + n*1.3%VDD 96 97 % VDD %VDD Clamping output Clamp high max See paragraph 6.4.3 for detailed high 0 explanation 3901090320 Rev 004 Page 5 of 32 Data Sheet Mar/05 MLX90320 Automotive small sensor interface Clamping output high1 7 other high clamping levels with a clamp level variation of 1.3%VDD for each n = [0..7] Clamp high max – 1.3%VDD % VDD Clamping output high n Clamp high max – n*1.3%VDD % VDD Parameter. Low diagnostic output High diagnostic output Symbol Diagnostic Limits Specifications Comments Min Typ 0 96 Max 4 Units %VDD %VDD Signal path general Specifications Parameter. Overall gain Symbol Comments See table 3 below for an overview Gdido Gdts Gcs Fine gain Sensor output span that can be accommodated to achieve 4V output span Fgain 1bit programmable 1bit programmable 1bit programmable 10 bit programmable Min 12.7 Typ Max 442 Units V/V Coarse gain 3.25 2 1.24 0.448 1.8 13 5 1.9375 0.99 63 V/V V/V V/V V/V mV/Vsupply Without an optimal compensation of the sensitivity temperature drift (i.e. with the fine gain equal to one of the extreme range values) With an optimal compensation of the sensitivity temperature drift (i.e. with the fine gain equal to the middle range value) Sensor output span that can be accommodated to achieve 4V output span 2.5 40 mV/Vsupply 3901090320 Rev 004 Page 6 of 32 Data Sheet Mar/05 MLX90320 Automotive small sensor interface Sensor offset that can be compensated Depends on gain settings and desired output offset voltage. See Table 3 below for an overview. 0.4 97.2 mV/Vsupply Output Offset programmable Output Offset resolution Overall non linearity Wake-up time at power up Output noise Output current capability Response time Set by an external capacitor Best fit value MLX90320 operational, in spec. 10nF FLT capacitance 10 90 0.1 ±0.1 %VDD %VDD %VDD ms 0 10 5 ± 2.5 0.1 mVrms mA ms 3901090320 Rev 004 Page 7 of 32 Data Sheet Mar/05 1 To be able to compensate the sensor sensitivity drift with temperature, the typical sensor output span that gives 4V as MLX90320 output span must be calculated for a fine gain in the middle of his range (i.e. 0.72 V/V) 3901090320 Rev 004 Page 8 of 32 Data Sheet Mar/05 Table 3 Gdido Gdts GCS Fine Gain V/V Typical Total Gain V/V 12.7 28.4 19.9 44.3 31.8 70.9 49.6 110.8 50.7 113.2 79.2 176.8 126.7 282.9 197.9 441.8 Sensor span in order to achieve 4V output span (mV) 1 Typical total sensor offset that can be compensated to achieve 0.5V as MLX90320 output offset (mV) -306.7 171.1 149.6 157.1 143.3 147.9 139.3 142.3 136.8 42.9 37.5 39.4 36.0 37.1 34.9 35.7 34.3 Typical total sensor offset that can be compensated to achieve 4.5V as MLX90320 output offset (mV) 8.0 -187.3 -119.3 -244.3 -204.1 -282.2 -255.0 -305.0 2.0 -47.0 -29.9 -61.3 -51.2 -70.8 -63.9 -76.5 485.9 290.6 358.6 233.6 273.9 195.7 222.9 172.9 121.9 72.9 90.0 58.6 68.7 49.1 55.9 43.4 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0.448 0.99 0.448 0.99 0.448 0.99 0.448 0.99 0.448 0.99 0.448 0.99 0.448 0.99 0.448 0.99 196.1 -328.3 -320.8 125.2 -334.6 -329.0 78.3 -338.6 -335.6 50.2 -341.1 -76.9 Automotive small sensor interface 49.1 -82.3 -80.4 31.5 -83.9 -82.7 MLX90320 19.7 -84.9 -84.2 12.6 -85.5 MLX90320 Automotive small sensor interface 6 Detailed Description Figure 1: General block diagram of the MLX90320 The MLX90320 can be used with almost any type of resistive bridge sensor without the need of any additional signal conditioning. The differential input signal is offset compensated and amplified to achieve the desired output voltage. With a coarse gain calibration the MLX90320 can easily accommodate sensor output spans in the 1.8mV/V to 63mV/V range to achieve 4 V output span. Sensor output offset in the 0.4mV/V to 97.2mV/V range (depending on the sensor output span and on the desired output offset, see table 3 for the details) can be compensated with the coarse offset calibration to achieve an output offset in the 0.5V to 4.5V range. Figure 2 shows two typical output characteristics that can be obtained with the calibration of the MLX90320. The option of swapping the inputs by setting one bit in EEPROM and the wide variation of the output offset with the coarse offset calibration allows calibrating a decreasing output characteristic as shown in figure 2. All output characteristics between those described in figure 2 can be achieved for a wide range of sensor output span and offset. 3901090320 Rev 004 Page 9 of 32 Data Sheet Mar/05 MLX90320 Automotive small sensor interface Figure 2: Two typical MLX90320 output characteristics obtained after calibration Besides the coarse gain and offset adjustment, the MLX90320 can accurately adjust the output span and offset to the desired values by calibrating a fine gain and a fine offset 10 bits DAC. This fine calibration allows also compensating second order temperature drifts of the sensor sensitivity and offset. An accurate temperature chain gives the information needed to compensate this temperature drift. The user has the possibility of selecting between an internal or external temperature sensor by setting one bit in EEPROM. What follows is the description of the different features of the MLX90320. For each feature the different calibrations parameters associated will be explained and their address in the EEPROM will be given. First the EEPROM will be described. 6.1 EEPROM The EEPROM is a 64 x 5 bits memory. A detailed description of the EEPROM memory address map is given in the paragraph 9. So each EEPROM address contains 4 calibration bits and one parity bit. The sum of the '1''s of the five bits must be '1'. That means that when data is '0000' the parity must be '1' (other examples:'0100' parity is '0'; '1100' parity is '1'; '1111' parity is '1'). 6.2 The programmable clock. The CLKADJ[3:0] bits are stored in address 3 of the EEPROM. These bits are used to program the oscillator. If CLKADJ[3:0] = 1111, the oscillator runs at the highest frequency. If CLKADJ[3:0] = 0000, the oscillator runs at the slowest frequency. This calibration is required to calibrate the 4 MHz oscillator within +/-15% accuracy. A bad oscillator calibration may cause malfunction of the communication protocol thus it is only factory set. 3901090320 Rev 004 Page 10 of 32 Data Sheet Mar/05 MLX90320 Automotive small sensor interface 6.3 The temperature chain. Figure 3 The temperature chain The temperature chain is composed of the temperature sensor, an amplifier with programmable gain and offset and a SAR ADC. The user can choose between an internal or an external temperature sensor. By setting the bit TMP_Select to 1 (EEPROM address 23) the internal temperature sensor is chosen and the TMP pin has to be left floating in application mode. If TMP_Select is 0 the external temperature sensor is chosen and an external resistor has to be connected between the supply voltage and the TMP pin. The MLX90320 should be used with an external temperature sensor only for applications where the temperature surrounding the customer sensor is different from the temperature surrounding the MLX90320. An example of external resistor that could be used in those specific applications is given in paragraph 8. As the sensitivity and the offset of the temperature sensor can vary a lot from part to part, the temperature chain must be calibrated. For that reason the amplifier gain is three bits programmable (TMP_GAIN bits stored in EEPROM address 31). These three bits are used to calibrate the sensitivity of the temperature chain. The amplifier offset is five bits programmable (TMP_OFFSET bits stored in EEPROM address 23 and 27) and compensates the offset of the temperature sensor. After calibration the output of the temperature chain amplifier must be within the input range of the SAR ADC for the entire application temperature range. When the calibration of the temperature chain is over, the 10 bits room temperature T1 can be stored in the EEPROM (address 0 to 3 for the T1 value used to calculate the fine gain and address 16 to 18 for T1 value used to calculate the fine offset) and it will be used for the sensor signal chain offset and sensitivity temperature drift compensation. 3901090320 Rev 004 Page 11 of 32 Data Sheet Mar/05 MLX90320 Automotive small sensor interface 6.4 The sensor signal chain. Figure 4 The sensor signal chain The input of the sensor signal chain is a differential voltage INP-INM. The differential inputs can be inverted by setting the IINV bit (EEPROM address 7). This is done by a 180º phase shift of the chopping signal. This allows calibrating a decreasing output characteristic instead of an increasing one as shows Figure 2. A dual input dual output 1 bit gain programmable amplifier (Gdido) is the first amplifier stage of the sensor signal chain. The use of noise and offset reduction techniques like chopping and sample and hold makes the contribution of the on-chip noise, offset and offset drift negligible compared to the same imperfections from the external sensor. A dual input single output 1 bit programmable gain amplifier (Gdts) and a 1 bit programmable gain charge summing amplifier (Gcs) completes the programmable coarse gain of the sensor signal chain. Thanks to the wide programmable coarse gain range, the MLX90320 can accommodate wide sensor output spans. A coarse and fine sensor offset compensation is done at the inputs of the dual to single amplifier (Gdts). A fine gain DAC allows calibrating accurately the output span. A wide range of sensor offsets can be compensated with the coarse offset calibration while the desired output offset can be achieved accurately with the fine offset calibration. The fine gain and offset calibration allows compensating a second order temperature drift of the sensor sensitivity and offset. An external capacitor connected to the FLT pin sets the bandwidth of the MLX90320. The global equations of the sensor signal chain are given below: POS OUT − NEGOUT = GDIDO × (INP − INM ), if _ IINV = 0 G DIDO × (INM − INP ), if _ IINV = 1 AGND = 0.7 × VDD DtsOUT = −GDTS × (POS OUT − NEGOUT ) + GnIN = FN GAIN × (CS OUT − AGND ) + AGND CS OUT = GCS × (DtsOUT GDTS × (FN OFF − CS OFF ) + AGND 3 − AGND ) + AGND GnOUT = 2.117 × (GnIN − AGND ) + AGND 3901090320 Rev 004 Page 12 of 32 Data Sheet Mar/05 MLX90320 Automotive small sensor interface OUT = −1.667 × GnOUT + 1.1668 × V DD Explanation of the parameters used in the global equations:   INP-INM is the differential output from the sensor IINV is the bit that swaps the MLX90320 inputs INP and INM POSout, NEGout, Dtsout, CSout, Gnin and Gnout are MLX90320 internal nodes represented in the schematic of the sensor signal chain (fig 5) AGND is an analog ground dependent of the supply voltage VDD. GDIDO, GDTS, GCS form the sensor signal chain coarse gain programmable. FNOFF and CSOFF are respectively the sensor signal chain fine and coarse offset programmable. FNGAIN i s the sensor signal chain fine gain programmable. OUT is the application mode output of the MLX90320.                         The different sensor chain calibration parameters with their range will be described in the following paragraphs. 6.4.1 The Gain calibration of the sensor signal chain. Three programmable coarse gain stages allow calibrating a wide range of sensor output spans (1.8mV/V to 63mV/V range) to the desired MLX90320 output span. Amplifier DIDO is a differential input – differential output amplifier, while amplifier DTS and CS are dual-to-single-ended amplifiers giving a single ended output voltage referred to the ground. Each one of these three amplifiers is one bit programmable: The DIDO gain is 3.25 or 13 depending on the value of the corresponding bit stored on the address 7 of the EEPROM. The DTS gain is 2 or 5 depending on the value of the corresponding bit stored on the address 7 of the EEPROM. The CS gain is 1.24 or 1.9375 depending on the value of the corresponding bit stored on the address 7 of the EEPROM. Besides the three programmable coarse gain stages, there is also a 10 bits programmable fine gain stage within the range 44.88% to 99%. The fine gain calibration allows an accurate adjustment of the output span. The fine gain can be calculated by the formula: FN GAIN = (0.448 + FNGain real × (0.99 − 0.448)) Equation 1 Explanation of parameters used in equation 1: FNGAIN i s the fine gain used in the signal sensor chain. FNGainreal i s the value of the fine gain in the [0..1] range with 10 bits resolution. The fine gain calibration allows also a second order compensation of the drift with temperature of the sensor sensitivity. The value of the fine gain is given by the formula: FNGainreal = G0 + G1 × (T − T1 ) + G2 × (T − T1 ) Equation 2 Explanation of parameters used in equation 2: 2 3901090320 Rev 004 Page 13 of 32 Data Sheet Mar/05 MLX90320 Automotive small sensor interface   T1 i s the output of the temperature chain corresponding to the room temperature. The ADC of the temperature chain outputs 10bits but 12 bits are stored (address 0 to 2 of the EEPROM). The MSB must always be 0 and the other 11 bits are obtained from an average of the previous temperature readings. This gives more accuracy to the output of the temperature chain. The T1 value used in equation 2 is in the [0..1] range with an 11 bit resolution.   G0 is the zero order fine gain coefficient (independent from the temperature) used to adjust accurately the output span at room temperature. 12 bits are stored (address 12 to 14 of the EEPROM) but only the 10 first are used. The two MSB must be 0. The G0 value used in equation 2 is in the [0..1] range with a 10 bit resolution.   G1 is the first order fine gain coefficient used to compensate the sensor sensitivity drift with temperature. 12 bits are stored (address 8 to 10 of the EEPROM). The MSB is the sign bit (two’s complement): If G1[11] = 1 then G1 is negative, if G1[11] = 0 then G1 is positive. The G1 value used in equation 2 is in the [-2..2] range with an 11 bit resolution.   G2 i s the second order fine gain coefficient used to compensate the sensor sensitivity drift with temperature. 12 bits are stored (address 4 to 6 of the EEPROM). The MSB is the sign bit (two’s complement): If G2[11] = 1 then G2 is negative, if G2[11] = 0 then G2 is positive. The G2 value used in equation 2 is in the [-2..2] range with an 11 bit resolution. The ALU computes equation 2 with 12 bits but the result is truncated to 10 bits because the Gain DAC is a 10 bit DAC. When the MLX90320 is not able to compensate for the sensor sensitivity drift with temperature, the fine gain calibration parameters stored in EEPROM will lead to a FNGainreal value out of the [0..1] range. In this case the MLX90320 output voltage will go into a fault band to indicate that the output voltage is not reliable anymore. Typical total gains with the corresponding sensor offset ranges that can be compensated can be found in table 3. 6.4.2 The Offset calibration of the sensor signal chain. The purpose of the 7-bit offset DAC is to be able to adjust the MLX90320 output offset anywhere in the 0.5V to 4.5V range. The voltage at the output of the coarse offset DAC can be calculated by the formula: CSOff ana log = 4.52 − Equation 3 CSOff digital 127 × (4.52 − 0.3) × VDD 5 Explanation of parameters used in equation 1:   CSOffanalog is the voltage at the output of the coarse offset DAC. CSOffdigital is the digital decimal value of the coarse offset (7 bits stored in address 11 and 15 of the EEPROM).   The voltage span at the output of the coarse offset DAC is large enough to allow the user to calibrate a decreasing output characteristic with for example 4.5V as output offset and 0.5V as output full scale. This output characteristic is only possible by inverting the inputs (setting the IINV bit). Besides the programmable coarse offset, there is also a 10-bits programmable fine offset stage which allows adjusting the MLX90320 output offset with a high resolution (at least a resolution of 0.1% of the supply voltage). The voltage at the output of the fine offset DAC can be calculated by the formula: 3901090320 Rev 004 Page 14 of 32 Data Sheet Mar/05 MLX90320 Automotive small sensor interface FNOff ana log = (1.136 + FNOff real × (1.59 − 1.136)) × Equation 4 Explanation of parameters used in equation 4:   VDD 5 FNOffanalog i s the voltage at the output of the fine offset DAC. FNOffreal i s the value of the fine offset in the [0..1] range with a 10 bit resolution.   The VDD term of equation 3 and 4 are due to the ratio-metric behaviour of the fine and coarse offset DACs. 5 The fine offset calibration allows also a second order compensation of the temperature drift of the sensor offset. The value of the fine offset is given by the formula: Equation 5 FNOff real = O0 + O1 × (T − T1 ) + O2 × (T − T1 ) Explanation of parameters used in equation 5:   2 T1 i s the output of the temperature chain corresponding to the room temperature. The ADC of the temperature chain outputs 10 bits but 12 bits are stored (address 0 to 2 of the EEPROM). The MSB must always be 0 and the other 11 bits are obtained from an averaging from the previous temperature readings. This gives more accuracy to the output of the temperature chain. The T1 value used in equation 5 is in the [0..1] range with an 11 bit resolution.   O0 is the zero order fine offset coefficient (independent from the temperature) used to compensate accurately the sensor offset at room temperature. 12 bits are stored (address 28 to 30 of the EEPROM) but only the 10 first are used. The two MSB must be 0. The O0 value used in equation 5 is in the [0..1] range with a 10 bit resolution.   O1 is the first order fine offset coefficient used to compensate the sensor offset drift with temperature. 12 bits are stored (address 24 to 26 of the EEPROM). The MSB is the sign bit (two’s complement): If O1[11] = 1 then O1 is negative, if O1[11] = 0 then O1 is positive. The O1 value used in equation 5 is in the [-2..2] range with an 11 bit resolution.   O2 is the second order fine offset coefficient used to compensate the sensor offset drift with temperature. 12 bits are stored (address 20 to 22 of the EEPROM). The MSB is the sign bit (two’s complement): If O2[11] = 1 then O2 is negative, if O2[11] = 0 then O2 is positive. The O2 value used in equation 5 is in the [-2..2] range with an 11 bit resolution. The ALU computes the equation 5 with 12 bits but the result is truncated to 10 bits because the Offset DAC is a 10 bit DAC. When the MLX90320 is not able to compensate for the sensor offset drift with temperature, the fine offset calibration parameters stored in EEPROM will lead to a FNOffreal value out of the [0..1] range. In this case the MLX90320 output voltage will go into a fault band to indicate that the output voltage is not reliable anymore. The MLX90320 also offers the possibility to set clamping levels to the output voltage. This allows creating fault bands necessary to detect external and internal faults. 6.4.3 The output clamping levels The output voltage is in application mode limited by a 3-bit programmable low and 3-bit programmable high clamping-level. In order to set the clamping level in a high impedance node, the clamping is done at the FLT pin. 3901090320 Rev 004 Page 15 of 32 Data Sheet Mar/05 MLX90320 Automotive small sensor interface The FLT pin voltage is compared with the DA-converted value of CLAMPLOWdig and CLAMPHIGHdig. If the FLT pin voltage is greater than the DA-converted value of CLAMPHIGHdig, then this last voltage is used as input of the output stage. If the FLT pin voltage is smaller than the DA-converted value of CLAMPLOWdig, then this last voltage is used as input of the output stage. The transition from in range mode to clamping mode and vice versa takes place without overshoot. The output pin low clamping level can be calculated by the formula : Equation 6 Voutlowclamp = (Lowclamp + Clamplowdig × 0.013) × VDD Explanation of parameters used in equation 6:   Voutlowclamp is the output pin low clamping voltage. Lowclamp is the lowest clamp level and has a typical value of 4% +/-1% variation from sample to sample. Clamplowdig is the decimal value (range of 0 to 7) of the low clamp level stored in EEPROM at the address 19.     The output pin high clamp level can be calculated by the formula: Equation 7 Vout highclamp = (Highclamp + (Clamphighdig − 7 )× 0.013)× VDD Explanation of parameters used in equation 7:   Vouthighclamp i s the output pin high clamping voltage. Highclamp i s the highest clamp level and has a typical value of 96% +/-1% variation from sample to sample. Clamphighdig is the decimal value (range of 0 to 7) of the high clamp level stored in EEPROM at the address 19 and 23.     6.4.4 The Faults detection As mentioned before, a reliable memory is obtained by storing each bit three times in the EEPROM and by using parity check to detect data corruption and majority voting when accessing the data. Thanks to the setting of output clamping levels, the MLX90320 output voltage goes to the fault bands to point out that a fault occurred and that the output signal is unreliable. The MLX90320 contains circuitry which detects and diagnoses the following faults with the loads as described and specified in and under the conditions of paragraph 5: Internal faults Fault detection of INP and INM have the levels at 1.5 and 3.5 Volt (with 5 Volt supply). • • • • • INP and/or INM open Sensing element supply open Short-circuit of INP and/or INM with VDD Short-circuit of INP and/or INM with GND Short-circuit of FLT with VDD or GND 3901090320 Rev 004 Page 16 of 32 Data Sheet Mar/05 MLX90320 Automotive small sensor interface When a short-circuit of FLT with VDD occurs the output goes to the high fault band. For all other internal faults the output goes to the low fault band. External faults Short-circuit • Output with VDD • Output with GND • Output with Vbat In all of these above mentioned fault cases, the IC will generate an output within either of the diagnostic bands. Open circuit • VDD open • GND open In case of open circuit the output will go to the high fault band. The MLX90320 must survive to the following reversed contacts but the output does not go to the fault bands. • Reverse polarity • Reverse battery polarity • Output reversed with GND • Output reversed with VDD 3901090320 Rev 004 Page 17 of 32 Data Sheet Mar/05 MLX90320 Automotive small sensor interface 6.5 Programming the MLX90320 through the output pin Communicating with the MLX90320 only requires a limited amount of interface circuitry, software and a computer. Melexis provides a communication equipment and belonging software such that the customer is able to start communicating with the chip in a matter of minutes. The output pin acts as analog output pin and as communication pin. The drive stage of a class AB amplifier is connected to that pin to output the analog output signal. For the communication the output will be sink/source current source. Through a short circuit detection, the ASSP knows that the user requests the pin for communication. 6.5.1 Overview When the user wants to communicate with the MLX90320, communication must be requested. This can be achieved by short-circuiting the output pin to ground and supply level. The ASSP detects this short and after a delay time, the same output pin turns into a half-duplex digital communication channel. 6.5.2 Communication Request 3901090320 Rev 004 Page 18 of 32 Data Sheet Mar/05 MLX90320 Automotive small sensor interface 1) Pattern to enter the communication mode Short-circuit to VDD analog signal Short-circuit to VDD Digital Signal COM pin : 1.5ms +30% Short-circuit to the GROUND Short-circuit to the GROUND 1.5ms +30%