Using the 56F83xx Temperature Sensor
Contents
1. Temperature Sensor Voltage Versus Time 1 82 25 1 8 1 78 20 _ 1 76 5 15 a 1 74 S 5 gt 1 72 ES 10 x 1 7 5 Q lt 1 68 5 1 66 1 64 0 0 100 200 300 400 seconds Figure 4 5 Estimated Tj Over Time B 5 Software Implementation The 56F83xx Analog to Digital Converter implementation has numerous modes of operation All these features are available to code which implements temperature sensing functions For instance the ADC can be set to continuously sample the temperature sensor voltage at some frequency comparing each conversion result with either the ADC high or low limit registers Exceeding either one or both values could then result in an interrupt service routine being called Thus either an under or over temperature alarm can be implemented with essentially zero software overhead on the main processing loop Code Example 5 1 illustrates the steps required to measure Tj 56F8300 ADC Rev 1 Freescale Semiconductor 9 Conclusion Code Example 5 1 Steps Required to Measure Tj define TSENSOR_CONTROL 0x00F270 define ADCA POWER 0x00F229 define ADCB POWER 0x00F269 define HFM IFROPT 2 0x00F41C define HFM JFROPT 0 Ox00F41A define ADCA ADCR1 0x00F200 define ADCA ADLST1 0x00F203 define ADCA ADSDIS 0x00F205 define ADCA ADSTAT 0x00F206 define ADCA ADRSLTO 0x00F209 0x0001 gt TSENSOR CONTROL enable temp sensor Ox00DO0 gt ADCA POWER turn2. Freescale Semiconductor reserves the right to make changes without further notice to any products herein Freescale Semiconductor makes no warranty representation or guarantee regarding the suitability of its products for any particular purpose nor does Freescale Semiconductor assume any liability arising out of the application or use of any product or circuit and specifically disclaims any and all liability including without limitation consequential or incidental damages Typical parameters that may be provided in Freescale Semiconductor data sheets and or specifications can and do vary in different applications and actual performance may vary over time All operating parameters including Typicals must be validated for each customer application by customer s technical experts Freescale Semiconductor does not convey any license under its patent rights nor the rights of others Freescale Semiconductor products are not designed intended or authorized for use as components in systems intended for surgical implant into the body or other applications intended to support or sustain life or for any other application in which the failure of the Freescale Semiconductor product could create a situation where personal injury or death may occur Should Buyer purchase or use Freescale Semiconductor products for any such unintended or unauthorized application Buyer shall indemnify and hold Freescale Semiconductor and its officers employees sub
3. on ADC A rrt lt HFYFM IFROPT 2 Room temperature trim value rht lt HYM IFROPT 0 Hot temperature trim value m 150 25 rht rrt Slope of the T vs ADC result curve b 150 n mre ee the y intercept 0x0004 gt ADCA_ADCR1 Triggered Sequential 0x7707 gt ADCA_ADLST1 ADLST1 set to sample ANA Ox00FC gt ADCA ADSDIS F enable only samplel 0 and 1 allow sufficient time for ADC reference and temperature sensor circuits to power up 25msec recommended 0x2004 gt ADCRI ADCR1 initiate the conversion status 0 wait for the conversion to complete while status not equal to 0x0803 status lt ADSTAT adc result lt ADCA ADRSLTO temperature m adc_result b Notes It is best to oversample and filter not shown 6 Conclusion The 56F83xx temperature sensor module provides a convenient and inexpensive way to adjust for temperature variances and restrictions The results obtained are subject to a number of limitations and proper system design based on the issues discussed in this application note can significantly increase its accuracy 1 References 1 56F8300 Peripheral User Manual MC56F8300UM 2 56F83xx Technical Data document specific to the device you re implementing MC56F83xx 3 DSP56800E Reference Manual DSP56800ERM 10 56F8300 ADC Rev 1 Freescale Semiconductor Self Heating 56F8300 ADC Rev 1 Freescale Semiconductor 11 How to Reach Us Home Page ww
4. represents the period at which the device is primarily heating just the package and the second is when heat transfer to the PC board dominates 1 Node TS was not bypassed on the bench used for these measurements This can account for some of the noise seen in the figures 56F8300 ADC Rev 1 Freescale Semiconductor 7 Accuracy Issues Temperature Sensor Voltage Versus Time 1 82 25 1 8 1 78 20 FX 1 76 e 2 1 74 G 23 1 72 s 10 8 1 7 5 1 68 5 2 1 66 1 64 0 0 10 20 30 40 seconds Figure 4 4 Estimated Tj Over Time A Because each device board combination will vary it is important not to focus too closely on the specific numbers shown The point to be taken 1s that given time the device Tj will rise significantly above ambient temperature Time to thermal equilibrium is measured in minutes although the initial burst of self heating occurs in only a few seconds Because of this characteristic Freescale measures trim values for the temperature sensor very early in the production test sequence before the bulk of self heating has occurred The trim values are typically completed during the first 20ms after the device 1s powered up 56F8300 ADC Rev 1 8 Freescale Semiconductor Self Heating Additionally it is important to note that the temperature sensor measures Tj of the 56F83xx devices It does NOT measure the ambient temperature
5. Freescale Semiconductor Application Note Using the 56F83xx Temperature Sensor Michael Stanley 1 Introduction The 56F83xx controllers developed by Freescale include an on chip temperature sensor This module generates an output voltage which 1s directly proportional to the internal junction temperature of the device Software running on the controller can measure this voltage using the on chip Analog to Digital Converter ADC and that measured value can then be used to calculate temperature 2 Features and Benefits The 56F83xx temperature sensor offers these benefits e Generates a temperature dependent voltage over the full temperature range specified for the device e Greater than 1 bit degree C sensitivity at 10 bits of resolution e Room and or hot temperature sensor trim values are stored in on chip non volatile memory at the factory e Can be used for intelligent power control powering down portions of the system when temperatures near specified maximums e Can be used as an input to temperature compensate other portions of the system e Works in concert with the on chip Analog to Digital Converter ADC 1 The 56F83xx Analog to Digital Converters actually have 12 bits of resolution therefore the sensitivity can be restated to be greater than 4 LSB degree C 2 Consult the Data Sheet for your specific device to determine how it was trimmed at the factory Freescale Semiconductor Inc 2005 All rig
6. RENEMEMUE ANNA 4 i i i f i i i 1 i i f i i ure COMORES AAA COLE NANOVO i i f i H i 1 mssememrmremsenen fo n pon ra i ft TA a oe 1 i 3 i i Adding an external 0 01 uF capacitor to the TS ADC input node eliminates this measurement error source completely 1 i f i i i Seog PST ML TE Figure 4 2 Temperature Sensor Output Droop i REX EEE yv i 5l 56F8300 ADC Rev 1 4 Freescale Semiconductor Temperature Sensor Output Impedance The workaround has four components e Adda 0 0luF capacitor to the sensor output ADC input node e Limit the time between ADC samples on this node to greater than or equal to lus e Allow at least 10ms after powering up the temperature sensor before initiating any measurements which allows the temperature sensor time to charge up the bypass capacitor e Program the ADC so that the channel assigned to the temperature sensor is never the last to be measured in any given measurement sequence These steps effectively remove any effects of the sensor output impedance from the measurement However an issue still exists for the 56F8322 in which the sensor output is not brought to a package pin In this case there are two alternatives e Live with the decreased accuracy Characterizations are not complete at the time of
7. analog supplies are essential for accurate results Additionally since temperature will be changing extremely slowly compared with virtually any other system input it can be oversampled to filter out much of the random noise Figure 4 3 summarizes 5 000 temperature sensor measurements that were taken of a device on a socketed board The device was first allowed to run at speed for 20 minutes in order to reach thermal equilibrium before the measurements were taken Note that the spread of measured values is approximately 23mV which corresponds to about 3 C Finally the value of the DIV field in ADCR2 controls the frequency of the ADC internal clock versus the master system peripheral clock The amount of noise showing up on ADC measurements can often be reduced by slight changes in the value of this prescaler The device shown Figure 4 3 was running with a DIV value of 7 under nominal conditions with a 0 0047uF bypass capacitor on TS The recommended bypass capacitor value is 0 01 uF 4 4 Trim Accuracy Specifications for Tgr and Typ are shown in Table 4 2 This variance must obviously be factored into the final calculated value for T 56F8300 ADC Rev 1 Freescale Semiconductor Self Heating Table 4 2 Environmental Conditions During Factory Trim Programming Temperature Nominal Value Variance ee ARE RS ON O Trim accuracy is also limited by self heating See Section 4 5 for details 4 5 Self Heating Because the 56F83xx device
8. ce connects the temperature sensor and ANA7 inside the package and that node is not brought outside the device Room temperature 25 C nominal and high temperature 125 C nominal for industrial devices 150 C nominal for automotive devices ADC measurements of the temperature sensor output voltage are stored in non volatile storage by Freescale during factory test These read only values are available in the HFM_IFROPT_2 and HFM IFROPT 0 registers respectively Given e Rpry value of HFM_IFROPT_2 ADC reading of Vrs at 25 C e Ryr value of HFM_IFROPT_0 ADC reading of Vrs at 125 C or 150 C e _R current ADC result of measuring Vrs then temperature T is approximated by Ts b where Equation 1 m RHT Rep 125 C 25 C and Equation 2 R b 125 C a Equation 3 56F8300 ADC Rev 1 D Freescale Semiconductor Temperature Sensor Output Impedance 4 Accuracy Issues There are a number of factors which affect the accuracy of measurements made using the temperature sensor These include inherent limitations of the device trim accuracy and board impacts and are discussed in the following subsections 4 1 Sensor Linearity There are two major blocks involved in taking a temperature measurement the temperature sensor block which generates the temperature dependent voltage and the Analog to Digital Converter which converts the value into digital form In a recent set of lab measurements the anal
9. hts reserved AN1980 Rev 1 9 2005 Contents 1 Introduction 1 2 Features and Benefits 1 RE ra 2 4 Accuracy ISSUES ccccccceeeseseeeees 3 4 1 Sensor Linearity 3 4 2 Temperature Sensor Output Impedance ns 3 4 3 Random Noise ccccccccsesssseeeeeeeeeees 6 4 4 Trim Accuracy essseeseeoseeesesseesseesreesee 6 4 5 Self Heating 7 5 Software Implementation 9 6 Conclusion oororoooooonnnnu 10 TAR BICTONCES nes serons 10 1o z freescale semiconductor Overview e When coupled with the ADC low and high limit registers can generate under and over temperature interrupts with no software overhead e Consumes minimum power and can be powered down if not required 3 Overview Use of the temperature sensor consumes an ADC input of the device In most members of the family all except the 56F8322 the temperature sensor voltage is brought directly to a package pin of the device The user 1s responsible for then shorting that pin to an ADC input In this manner the user can choose which function is more important to his particular application S6F83xx 0 011 bypass cap Figure 3 1 Typical 56F83xx Temperature Sensor Connections In Figure 3 1 TS is the temperature sensor output pin ANA is input 7 to Analog to Digital Converter A The 56F8322 devi
10. og output voltage of the sensor was oversampled by 10x at 25 C 125 C 135 C and 150 C for a number of wat ede The averages of each of those temperatures was used to extract an equation for each individual device The standard error of estimate about those lines ranged from 2 6mV to 8 3mV as shown in Table 4 1 Table 4 1 Variance in Measured Temperature Sensor Analog Voltage VHT s V C k V Standard Error of s C 135 C Estimate V Average na 0 00746 1 1429 00046 0046 Minimum 1 576 0 00729 ES nu Maximum 1 684 0 00769 1 498 0 0083 Table 4 1 dealt with the temperature sensor voltage as measured by an external monitor In practice the on chip ADC will be used to perform this conversion The 56F83xx family s ADCs are expected to operate with an effective number of bits ENOB of 9 or 10 Assuming 3 3V full range for the ADC this equates to 3 2 to 6 4mV accuracy for the ADC conversion itself 4 2 Temperature Sensor Output Impedance The 56F83xx temperature sensor was designed to use a minimum amount of power A fairly high output impedance was the design trade off made Figure 4 1 illustrates the limited drive capability of this module The typical application externally connects the temperature sensor output to an ADC input The 56F83xx ADC has a switched capacitor sample and hold circuit in its input stage When this switch closes at the rising edge of the ADC s sample clock there can be an instantane
11. ous current required to charge up the sampling capacitor Though this capacitor is quite small the high output impedance of the temperature sensor s output can result in a disturbance of the node s voltage as shown in Figure 4 2 Adding a 0 01uF bypass capacitor to the temperature sensor output ADC input node effectively mitigates this error source However if the ADC is used to sample the node continuously and at a high enough frequency the temperature sensor output will see a low load impedance and this source of measurement error will re manifest itself 1 V s T k where s is in volts degree C T is in degrees C and k is in volts 56F8300 ADC Rev 1 Freescale Semiconductor 3 Accuracy Issues Temperature Sense Pin IV Curve Figure 4 1 Temperature Sensor Output I V Curve P Oe a Sl ob ADC input sampling cap switch Cap switch opens This is the _ Closes creating instantaneous voltage that the ADC will current demand from Temp _ convert Sense output t St The ADC clock would have to be run T ata very low frequency to avoid measuring this perturbation The 17 switch open point would have to be placed out here j i i i i i te f i i f i i j j i f i j i i iila P tliat Pilil Eki of AJE EL wae UN ey Unt a SR lo alu d i i f i i i f i i f i f u doOMON
12. s draw non zero supply current they consume power and are therefore subject to self heating For example assume Vpp 3 3V Ipp 120mA Thetay 40 C W The device can then be expected to have a junction to ambient temperature difference of 3 3 x 12 x 40 16 C Ipp is a function of device type frequency of operation code being executed number of peripherals enabled and Vpp among other things Accurate estimation of 56F83xx power dissipation will be addressed in a separate application note Likewise Thetay is a function of the device package heat sink board design TA and Tr See the device Data Sheet for further information One question which arises is Just how fast does the device self heat after power up An experiment was performed in an effort to answer this A 56F83xx device was placed in a low power Stop mode assumed to have minimal self heating and allowed some time to reach thermal equilibrium The mode was then switched to Run at 6 0MHz and the temperature sensor sampled at regular intervals These readings can be used with Equations 1 through 3 See Section 3 to calculate Tj Both Vrs and Tj are shown in Figure 4 4 and Figure 4 5 The data is the same for both figures although Figure 4 4 has an expanded time scale to focus on the initial seconds From these it 1s apparent that the device has an initial burst of self heating followed by a slower ramp rate upward It seems logical to assume that the first
13. sidiaries affiliates and distributors harmless against all claims costs damages and expenses and reasonable attorney fees arising out of directly or indirectly any claim of personal injury or death associated with such unintended or unauthorized use even if such claim alleges that Freescale Semiconductor was negligent regarding the design or manufacture of the part s z freescale semiconductor Freescale and the Freescale logo are trademarks of Freescale Semiconductor Inc All other product or service names are the property of their respective owners This product incorporates SuperFlash technology licensed from SST Freescale Semiconductor Inc 2005 All rights reserved AN1980 Rev 1 9 2005
14. this writing but measurements made on an early 56F8345 device with no bypass capacitor on the temperature sensor output indicates that the standard error of estimate for the converted voltage may increase to 60mV or more e Lower the ADC clock rate so that the sample hold circuit closes after the sensor has recharged the internal switched cap circuits effectively bypassing the droop Decreasing the ADC clock rate to 125KHz or slower should take care of this problem 1 During some modes of operation the 56F83xx ADC sample amp hold circuit will continuously sample the last input s listed in the ADC Channel List registers between sample periods For this reason the chan nel assigned for use in sampling the temperature sensor voltage should never be the last channel sam pled 56F8300 ADC Rev 1 Freescale Semiconductor 5 Accuracy Issues 4 3 Random Noise 56F8357 Temp Sensor Voltage Histogram of RT under power measurements 5000 600 500 Maximum 1 948096 Mean 1 938688 Minimum 1 925537 400 StdDev 0 002976 Max Min 0 0226 3 300 o D Bam u 200 100 0 O ND V O KR U S MW A A t S O O DO O O O O O o DOD re wr Vw VY VY LYK Ww PV PLY LY Tr Te Figure 4 3 Temperature Sensor Voltage as Measured by the ADC The printed circuit board layout must be considered in any system that performs Analog to Digital conversions as short traces and clean
15. w freescale com E mail support freescale com USA Europe or Locations Not Listed Freescale Semiconductor Technical Information Center CH370 1300 N Alma School Road Chandler Arizona 85224 1 800 521 6274 or 1 480 768 2130 support freescale com Europe Middle East and Africa Freescale Halbleiter Deutschland GmbH Technical Information Center Schatzbogen 7 81829 Muenchen Germany 44 1296 380 456 English 46 8 52200080 English 49 89 92103 559 German 33 1 69 35 48 48 French support freescale com Japan Freescale Semiconductor Japan Ltd Headquarters ARCO Tower 15F 1 8 1 Shimo Meguro Meguro ku Tokyo 153 0064 Japan 0120 191014 or 81 3 5437 9125 support japan freescale com Asia Pacific Freescale Semiconductor Hong Kong Lid Technical Information Center 2 Dai King Street Tai Po Industrial Estate Tai Po N T Hong Kong 800 2666 8080 support asia freescale com For Literature Requests Only Freescale Semiconductor Literature Distribution Center P O Box 5405 Denver Colorado 80217 1 800 441 2447 or 303 675 2140 Fax 303 675 2150 LDCForFreescaleSemiconductor hibbertgroup com Information in this document is provided solely to enable system and software implementers to use Freescale Semiconductor products There are no express or implied copyright licenses granted hereunder to design or fabricate any integrated circuits or integrated circuits based on the information in this document
Download Pdf Manuals
Related Search