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general description the max1452 is a highly integrated analog-sensor sig- nal processor optimized for industrial and process con- trol applications utilizing resistive element sensors. the max1452 provides amplification, calibration, and tem- perature compensation that enables an overall perfor- mance approaching the inherent repeatability of the sensor. the fully analog signal path introduces no quan- tization noise in the output signal while enabling digitally controlled trimming with the integrated 16-bit dacs. offset and span are calibrated using 16-bit dacs, allowing sensor products to be truly interchangeable. the max1452 architecture includes a programmable sensor excitation, a 16-step programmable-gain ampli- fier (pga), a 768-byte (6144 bits) internal eeprom, four 16-bit dacs, an uncommitted op amp, and an on- chip temperature sensor. in addition to offset and span compensation, the max1452 provides a unique tem- perature compensation strategy for offset tc and fsotc that was developed to provide a remarkable degree of flexibility while minimizing testing costs. the max1452 is packaged for the commercial, industri- al, and automotive temperature ranges in 16-pin ssop/ tssop and 24-pin tqfn packages. customization maxim can customize the max1452 for high-volume dedicated applications. using our dedicated cell library of more than 2000 sensor-specific functional blocks, maxim can quickly provide a modified max1452 solu- tion. contact maxim for further information. applications pressure sensors transducers and transmitters strain gauges pressure calibrators and controllers resistive elements sensors accelerometers humidity sensors outputs supported 4?0ma 0 to +5v (rail-to-rail) +0.5v to +4.5v ratiometric +2.5v to ?.5v features ? provides amplification, calibration, and temperature compensation ? accommodates sensor output sensitivities from 4mv/v to 60mv/v ? single pin digital programming ? no external trim components required ? 16-bit offset and span calibration resolution ? fully analog signal path ? on-chip lookup table supports multipoint calibration temperature correction ? supports both current and voltage bridge excitation ? fast 150 s step response ? on-chip uncommitted op amp ? secure-lock? prevents data corruption ? low 2ma current consumption secure-lock is a trademark of maxim integrated products, inc. part temp range pin-package MAX1452Cae+ 0? to +70? 16 ssop max1452eae+ -40? to +85? 16 ssop max1452aae+ -40? to +125? 16 ssop max1452aue+ -40? to +125? 16 tssop max1452atg+ -40? to +125? 24 tqfn-ep* MAX1452C/d 0? to +70? dice** max1452 low-cost precision sensor signal conditioner ________________________________________________________________ maxim integrated products 1 19-1829 rev 2 4/09 evaluation kit available for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. ordering information + denotes a lead(pb)-free/rohs-compliant package. * ep = exposed pad. ** dice are tested at t a = +25?, dc parameters only. detailed block diagram and pin configurations appear at the end of data sheet.
max1452 low-cost precision sensor signal conditioner 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v dd = v ddf = +5v, v ss = 0v, t a = +25?, unless otherwise noted.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. supply voltage, v dd to v ss .........................................-0.3v, +6v supply voltage, v dd to v ddf ................................-0.5v to +0.5v all other pins ...................................(v ss - 0.3v) to (v dd + 0.3v) short-circuit duration, fsotc, out, bdr, ampout ................................................................continuous continuous power dissipation (t a = +70?) 16-pin ssop/tssop (derate 8.00mw/? above +70?) ..640mw 24-pin tqfn (derate 20.8mw/? above +70?) ...........1.67w operating temperature: MAX1452Cae+/MAX1452C/d ............................0? to +70? max1452eae+ ................................................-40? to +85? max1452aae+ ..............................................-40? to +125? max1452aue+..............................................-40? to +125? max1452atg+..............................................-40? to +125? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) ................................ +300? parameter symbol conditions min typ max units general characteristics supply voltage v dd 4.5 5.0 5.5 v eeprom supply voltage v ddf 4.5 5.0 5.5 v supply current i dd (note 1) 2.0 2.5 ma maximum eeprom erase/write current i ddfw 30 ma maximum eeprom read current i ddfr 12 ma oscillator frequency f osc 0.85 1 1.15 mhz analog input input impedance r in 1m input referred offset tempco (notes 2, 3) 1 ?/ c input referred adjustable offset range offset tc = 0 at minimum gain (note 4) 150 mv amplifier gain nonlinearity p er cent of + 4v sp an, v ou t = + 0.5v to 4.5v 0.01 % common-mode rejection ratio cmrr specified for common-mode voltages between v ss and v dd (note 2) 90 db input referred adjustable fso range (note 5) 4 to 60 mv/v analog output differential signal-gain range selectable in 16 steps 39 to 234 v/v configuration [5:2] 0000bin 34 39 46 configuration [5:2] 0001bin 47 52 59 configuration [5:2] 0010bin 58 65 74 configuration [5:2] 0100bin 82 91 102 differential signal gain configuration [5:2] 1000bin 133 143 157 v/v maximum output-voltage swing no load from each supply 0.02 v
max1452 low-cost precision sensor signal conditioner _______________________________________________________________________________________ 3 electrical characteristics (continued) (v dd = v ddf = +5v, v ss = 0v, t a = +25?, unless otherwise noted.) parameter symbol conditions min typ max units output-voltage low i out = 1ma sinking, t a = t min to t max 0.100 0.20 v output-voltage high i ou t = 1m a sour ci ng , t a = t m in to t m ax 4.75 4.87 v output impedance at dc 0.1 output offset ratio v out / offset 0.90 1.05 1.20 v/v output offset tc ratio v ou t / offset tc 0.9 1 1.2 v/v step response and ic (63% final value) 150 ? maximum capacitive load 1f output noise dc to 1khz (gain = minimum, source impedance = 5k v ddf filter) 0.5 m v rms bridge drive bridge current i bdr r l = 1.7k 0.1 0.5 2 ma current mirror ratio aa r isource = internal 10 12 14 a/a v span range (span code) t a = t min to t max 4000 c000 hex digital-to-analog converters dac resolution 16 bits odac bit weight v out / code dac reference = v dd = +5.0v 76 ?/bit otcdac bit weight v out / code dac reference = v bdr = +2.5v 38 ?/bit fsodac bit weight v out / code dac reference = v dd = +5.0v 76 ?/bit fsotcdac bit weight v out / code dac reference = v bdr = +2.5v 38 ?/bit coarse offset dac irodac resolution including sign 4 bits irodac bit weight v out / code input referred, dac reference = v dd = +5.0v (note 6) 9 mv/bit fsotc buffer minimum output-voltage swing no load v ss + 0.1 v maximum output-voltage swing no load v d d - 1.0 v current drive v fsotc = +2.5v -40 +40 ? internal resistors current-source reference resistor r isrc 75 k
max1452 low-cost precision sensor signal conditioner 4 _______________________________________________________________________________________ note 1: excludes sensor or load current. note 2: all electronics temperature errors are compensated together with sensors errors. note 3: the sensor and the max1452 must be at the same temperature during calibration and use. note 4: this is the maximum allowable sensor offset. note 5: this is the sensor's sensitivity normalized to its drive voltage, assuming a desired full span output of +4v and a bridge volt- age range of +1.7v to +4.25v. note 6: bit weight is ratiometric to v dd . note 7: programming of the eeprom at room temperature is recommended. note 8: allow a minimum of 6ms elapsed time before sending any command. electrical characteristics (continued) (v dd = v ddf = +5v, v ss = 0v, t a = +25?, unless otherwise noted.) parameter symbol conditions min typ max units c ur r ent- s our ce refer ence resi stor tem p er atur e c oeffi ci ent r is rc 1300 p p m/c fsotc resistor r ftc 75 k fsotc resistor tem p er atur e c oeffi ci ent r ftc 1300 p p m/c temperature-to-digital converter temperature adc resolution 8 bits offset 3 lsb gain 1.45 c/bit nonlinearity 0.5 lsb lowest digital output 00 hex highest digital output af hex uncommitted op amp open-loop gain r l = 100k 90 db input common-mode range v ss v dd v output swing no load, t a = t min to t max v ss + 0.02 v dd - 0.02 v output-voltage high 1ma source, t a = t min to t max 4.85 4.90 v output-voltage low 1ma sink, t a = t min to t max 0.05 0.15 v offset v in+ = +2.5v, unity gain buffer -20 +20 mv unity gain bandwidth 2 mhz eeprom maximum erase/write cycles (note 7) 10k cycles minimum erase time (note 8) 6 ms minimum write time 100 ?
max1452 low-cost precision sensor signal conditioner _______________________________________________________________________________________ 5 typical operating characteristics (v dd = +5v, t a = +25?, unless otherwise noted.) pin ssop/tssop tqfn-ep name function 1 1 isrc bridge drive current mode setting 2 2 out high esd and scan path output signal. may need a 0.1? capacitor, in noisy environments. out may be parallel connected to dio. 33v ss negative supply voltage 4 4 inm bridge negative input. can be swapped to inp by configuration register. 5 5 bdr bridge drive 6 6 inp bridge positive input. can be swapped to inm by configuration register. 77v dd positive supply voltage. connect a 0.1? capacitor from v dd to v ss . 8, 9, 13, 16, 20, 22, 23, 24 n.c. no connection. not internally connected; leave unconnected (tqfn package only). 8 10 test internally connected. connect to v ss . pin description offset dac dnl max1452 toc01 dac code dnl (mv) 0 30k 40k 10k 20k 50k 60k 70k 5.0 2.5 0 -2.5 -5.0 5.0 2.5 0 -2.5 -5.0 amplifier gain nonlinearity max1452 toc02 input voltage [inp - inm] (mv) output error from straight line (mv) -50 0 -40 -30 -20 -10 10 20 30 40 50 odac = 6250hex otcdac = 0 fsodac = 4000hex fsotcdac = 8000hex pga index = 0 iro = 2 output noise max1452 toc03 400 s/div c = 4.7 f, r load = 1k out 10mv/div
max1452 detailed description the max1452 provides amplification, calibration, and temperature compensation to enable an overall perfor- mance approaching the inherent repeatability of the sensor. the fully analog signal-path introduces no quantization noise in the output signal while enabling digitally controlled trimming with the integrated 16-bit dacs. offset and span can be calibrated to within ?.02% of span. the max1452 architecture includes a programmable sensor excitation, a 16-step programmable-gain ampli- fier (pga), a 768-byte (6144 bits) internal eeprom, four 16-bit dacs, an uncommitted op amp, and an on-chip temperature sensor.the max1452 also provides a unique temperature compensation strategy for offset tc and fsotc that was developed to provide a remarkable degree of flexibility while minimizing testing costs. the customer can select from one to 114 temperature points to compensate their sensor. this allows the lati- tude to compensate a sensor with a simple first order linear correction or match an unusual temperature curve. programming up to 114 independent 16-bit eep- rom locations corrects performance in 1.5? tempera- ture increments over a range of -40? to +125?. for sensors that exhibit a characteristic temperature perfor- mance, a select number of calibration points can be used with a number of preset values that define the temperature curve. in cases where the sensor is at a different temperature than the max1452, the max1452 uses the sensor bridge itself to provide additional tem- perature correction. the single pin, serial digital input-output (dio) commu- nication architecture and the ability to timeshare its activity with the sensor? output signal enables output sensing and calibration programming on a single line by parallel connecting out and dio. the max1452 provides a secure-lock feature that allows the cus- tomer to prevent modification of sensor coefficients and the 52-byte user definable eeprom data after the sen- sor has been calibrated. the secure-lock feature also provides a hardware override to enable factory rework and recalibration by assertion of logic high on the unlock pin. the max1452 allows complete calibration and sensor verification to be performed at a single test station. once calibration coefficients have been stored in the max1452, the customer can choose to retest in order to verify performance as part of a regular qa audit or to generate final test data on individual sensors. the max1452? low current consumption and the inte- grated uncommitted op amp enables a 4?0ma output signal format in a sensor that is completely powered from a 2-wire current loop. frequency response can be user-adjusted to values lower than the 3.2khz band- width by using the uncommitted op amp and simple passive components. the max1452 (figure 1) provides an analog amplifica- tion path for the sensor signal. it also uses an analog architecture for first-order temperature correction. a digitally controlled analog path is then used for nonlin- ear temperature correction. calibration and correction is achieved by varying the offset and gain of a pro- grammable-gain-amplifier (pga) and by varying the low-cost precision sensor signal conditioner 6 _______________________________________________________________________________________ pin description (continued) pin ssop/tssop tqfn-ep name function 911v ddf positive supply voltage for eeprom. connect a 1? capacitor from v ddf to v ss . connect v ddf to v dd or for improved noise performance connect a 30 resistor to v dd . 10 12 unlock secure-lock disable. allows communication to the device. 11 14 dio digital input output. dio allows communication with the device. 12 15 clk1m 1mhz clock output. the output can be controlled by a configuration bit. 13 17 ampout uncommitted amplifier output 14 18 amp- uncommitted amplifier negative input 15 19 amp+ uncommitted amplifier positive input 16 21 fsotc full span tc buffered output ep exposed pad (tqfn only). internally connected; connect to v ss .
sensor bridge excitation current or voltage. the pga utilizes a switched capacitor cmos technology, with an input referred offset trimming range of more than ?50mv with an approximate 3? resolution (16 bits). the pga provides gain values from 39v/v to 234v/v in 16 steps. the max1452 uses four 16-bit dacs with calibration coefficients stored by the user in an internal 768 x 8 eeprom (6144 bits). this memory contains the follow- ing information, as 16-bit wide words: configuration register offset calibration coefficient table offset temperature coefficient register fso (full-span output) calibration table fso temperature error correction coefficient register 52 bytes (416 bits) uncommitted for customer pro- gramming of manufacturing data (e.g., serial num- ber and date) offset correction initial offset correction is accomplished at the input stage of the signal gain amplifiers by a coarse offset setting. final offset correction occurs through the use of a temperature indexed lookup table with 176 16-bit entries. the on-chip temperature sensor provides a unique 16-bit offset trim value from the table with an indexing resolution of approximately 1.5? from -40? to +125?. every millisecond, the on-chip temperature sensor provides indexing into the offset lookup table in eeprom and the resulting value transferred to the off- set dac register. the resulting voltage is fed into a summing junction at the pga output, compensating the sensor offset with a resolution of ?6? (?.0019% fso). if the offset tc dac is set to zero then the maxi- mum temperature error is equivalent to one degree of temperature drift of the sensor, given the offset dac has corrected the sensor at every 1.5?. the tempera- ture indexing boundaries are outside of the specified absolute maximum ratings . the minimum indexing value is 00hex corresponding to approximately -69?. all temperatures below this value output the coefficient value at index 00hex. the maximum indexing value is afhex, which is the highest lookup table entry. all tem- peratures higher than approximately 184? output the highest lookup table index value. no indexing wrap- around errors are produced. fso correction two functional blocks control the fso gain calibration. first, a coarse gain is set by digitally selecting the gain of the pga. second, fso dac sets the sensor bridge current or voltage with the digital input obtained from a temperature-indexed reference to the fso lookup table in eeprom. fso correction occurs through the use of a temperature indexed lookup table with 176 16-bit entries. the on-chip temperature sensor provides a unique fso trim from the table with an indexing resolu- tion approaching one 16-bit value at every 1.5? from -40? to +125?. the temperature indexing boundaries are outside of the specified absolute maximum ratings . the minimum indexing value is 00hex corre- sponding to approximately -69?. all temperatures below this value output the coefficient value at index 00hex. the maximum indexing value is afhex, which is the highest lookup table entry. all temperatures higher than approximately 184? output the highest lookup table index value. no indexing wrap-around errors are produced. max1452 low-cost precision sensor signal conditioner _______________________________________________________________________________________ 7 max1452 bias generator oscillator 16 bit dac - offset tc 16 bit dac - offset (176) 16 bit dac - fso (176) point 16 bit dac - fso tc anamux fsotc 176 temperature look up points for offset and span. op-amp a = 1 ampout v ss out v dd clk1m test internal eeprom 6144 bits 416 bits for user bdr pga v ddf v dd bdr dio unlock amp+ amp- inp isrc inm 8-bit adc temp sensor iro dac current source v dd figure 1. functional diagram
max1452 linear and nonlinear temperature compensation writing 16-bit calibration coefficients into the offset tc and fsotc registers compensates first-order tempera- ture errors. the piezoresistive sensor is powered by a current source resulting in a temperature-dependent bridge voltage due to the sensor's temperature resis- tance coefficient (tcr). the reference inputs of the off- set tc dac and fsotc dac are connected to the bridge voltage. the dac output voltages track the bridge voltage as it varies with temperature, and by varying the offset tc and fsotc digital code a portion of the bridge voltage, which is temperature dependent, is used to compensate the first order temperature errors. the internal feedback resistors (r isrc and r stc ) for fso temperature compensation are optimized to 75k for silicon piezoresistive sensors. however, since the required feedback resistor values are sensor dependent, external resistors may also be used. the internal resis- tors selection bit in the configuration register selects between internal and external feedback resistors. to calculate the required offset tc and fsotc com- pensation coefficients, two test-temperatures are need- ed. after taking at least two measurements at each temperature, calibration software (in a host computer) calculates the correction coefficients and writes them to the internal eeprom. with coefficients ranging from 0000hex to ffffhex and a +5v reference, each dac has a resolution of 76?. two of the dacs (offset tc and fsotc) utilize the sen- sor bridge voltage as a reference. since the sensor bridge voltage is approximately set to +2.5v the fsotc and offset tc exhibit a step size of less than 38?. for high accuracy applications (errors less than 0.25%), the first-order offset and fso tc error should be compensated with the offset tc and fsotc dacs, and the residual higher order terms with the lookup table. the offset and fso compensation dacs provide unique compensation values for approximately 1.5? of temperature change as the temperature indexes the address pointer through the coefficient lookup table. changing the offset does not effect the fso, however changing the fso affects the offset due to nature of the bridge. the temperature is measured on both the max1452 die and at the bridge sensor. it is recom- mended to compensate the first-order temperature errors using the bridge sensor temperature. typical ratiometric operating circuit ratiometric output configuration provides an output that is proportional to the power supply voltage. this output can then be applied to a ratiometric adc to produce a digital value independent of supply voltage. ratiometricity is an important consideration for battery- operated instruments, automotive, and some industrial applications. the max1452 provides a high-performance ratiometric output with a minimum number of external components (figure 2). these external components include the fol- lowing: one supply bypass capacitor. one optional output emi suppression capacitor. two optional resistors, r isrc and r stc , for special sensor bridge types. low-cost precision sensor signal conditioner 8 _______________________________________________________________________________________ figure 2. basic ratiometric output configuration max1452 +5v v dd out gnd r stc r isrc 0.1 f 0.1 f inm test v ss inp 7 9 2 16 1 8 3 bdr v ddf out 5 6 4 fsotc isrc sensor v dd
typical nonratiometric operating circuit (12vdc < vpwr < 40vdc) nonratiometric output configuration enables the sensor power to vary over a wide range. a high performance voltage reference, such as the max15006b, is incorpo- rated in the circuit to provide a stable supply and refer- ence for max1452 operation. a typical example is shown in figure 3. nonratiometric operation is valuable when wide ranges of input voltage are to be expected and the system a/d or readout device does not enable ratiometric operation. typical 2-wire, loop powered, 4?0ma operating circuit process control systems benefit from a 4?0ma current loop output format for noise immunity, long cable runs, and 2-wire sensor operation. the loop voltages can range from 12vdc to 40vdc and are inherently nonra- tiometric. the low current consumption of the max1452 allows it to operate from loop power with a simple 4?0ma drive circuit efficiently generated using the integrated uncommitted op amp (figure 4). internal calibration registers (icrs) the max1452 has five 16-bit internal calibration regis- ters that are loaded from eeprom, or loaded from the serial digital interface. data can be loaded into the internal calibration regis- ters under three different circumstances. normal operation, power-on initialization sequence the max1452 has been calibrated, the secure- lock byte is set (cl[7:0] = ffhex) and unlock is low. power is applied to the device. the power-on-reset functions have completed. registers config, otcdac, and fsotcdac are refreshed from eeprom. registers odac, and fsodac are refreshed from the temperature indexed eeprom locations. normal operation, continuous refresh the max1452 has been calibrated, the secure- lock byte has been set (cl[7:0] = ffhex) and unlock is low. power is applied to the device. the power-on-reset functions have completed. the temperature index timer reaches a 1ms time period. max1452 low-cost precision sensor signal conditioner _______________________________________________________________________________________ 9 max1452 vpwr +12v to +40v out gnd r stc r isrc 1.0 f 2.2 f 0.1 f 0.1 f inm test v ss inp 7 9 2 16 1 8 3 bdr v ddf out 5 6 4 fsotc isrc sensor max15006b out gnd 1 5 in 8 30 v dd g s d 2n4392 figure 3. basic nonratiometric output configuration
max1452 registers config, otcdac, and fsotcdac are refreshed from eeprom. registers odac and fsodac are refreshed from the temperature indexed eeprom locations. calibration operation, registers updated by serial communications the max1452 has not had the secure-lock byte set (cl[7:0] = 00hex) or unlock is high. power is applied to the device. the power-on-reset functions have completed. the registers can then be loaded from the serial digital interface by use of serial commands. see the section on serial interface command format . internal eeprom the internal eeprom is organized as a 768 by 8-bit memory. it is divided into 12 pages, with 64 bytes per page. each page can be individually erased. the mem- ory structure is arranged as shown in table 1. the look- up tables for odac and fsodac are also shown, with the respective temp-index pointer. note that the odac table occupies a continuous segment, from address 000hex to address 15fhex, whereas the fsodac table is divided in two parts, from 200hex to 2ffhex, and from 1a0hex to 1ffhex. with the exception of the gen- eral purpose user bytes, all values are 16-bit wide words formed by two adjacent byte locations (high byte and low byte). the max1452 compensates for sensor offset, fso, and temperature errors by loading the internal calibration registers with the compensation values. these compen- sation values can be loaded to registers directly through the serial digital interface during calibration or loaded automatically from eeprom at power-on. in this way the device can be tested and configured during calibration and test and the appropriate compensation values low-cost precision sensor signal conditioner 10 ______________________________________________________________________________________ max1452 v in+ +12v to +40v 2n2222a 47 100k 4.99k 4.99m 30 100 499k 100k v in- r stc r isrc 1.0 f 2.2 f 0.1 f 0.1 f 0.1 f inm test v ss inp 7 9 16 1 2 13 14 15 8 3 bdr v ddf v dd 5 6 4 fsotc isrc sensor max15006b out gnd 1 d s g 5 z1 in 2n4392 8 out ampout amp- amp+ figure 4. basic 4?0ma output, loop-powered configuration
stored in internal eeprom. the device auto-loads the registers from eeprom and be ready for use without fur- ther configuration after each power-up. the eeprom is configured as an 8-bit wide array so each of the 16-bit registers is stored as two 8-bit quantities. the configura- tion register, fsotcdac and otcdac registers are loaded from the pre-assigned locations in the eeprom. max1452 low-cost precision sensor signal conditioner ______________________________________________________________________________________ 11 table 1. eeprom memory address map page low-byte address (hex) high-byte address (hex) temp-index[7:0] (hex) contents 000 001 00 0 03e 03f 1f 040 041 20 1 07e 07f 3f 080 081 40 2 0be 0bf 5f 0c0 0c1 60 3 0fe 0ff 7f 100 101 80 4 13e 13f 9f 140 141 a0 15e 15f af to ff odac lookup table 160 161 configuration 162 163 reserved 164 165 otcdac 166 167 reserved 168 169 fsotcdac 16a 16b control location 16c 16d 5 17e 17f 180 181 19e 19f 52 general-purpose user bytes 1a0 1a1 80 6 1be 1bf 8f 1c0 1c1 90 7 1fe 1ff af to ff 200 201 00 8 23e 23f 1f 240 241 20 9 27e 27f 3f 280 281 40 a 2be 2bf 5f 2c0 2c1 60 b 2fe 2ff 7f fsodac lookup table
max1452 the odac and fsodac are loaded from the eeprom lookup tables using an index pointer that is a function of temperature. an adc converts the integrated tem- perature sensor output to an 8-bit value every 1ms. this digitized value is then transferred into the temp-index register. the typical transfer function for the temp-index is as fol- lows: temp-index = 0.6879 ? temperature (?) + 44.0 where temp-index is truncated to an 8-bit integer value. typical values for the temp-index register are given in table 6. note that the eeprom is byte wide and the registers that are loaded from eeprom are 16 bits wide. thus each index value points to two bytes in the eeprom. maxim programs all eeprom locations to ffhex with the exception of the oscillator frequency setting and secure-lock byte. osc[2:0] is in the configuration register (table 3). these bits should be maintained at the factory preset values. programming 00hex in the secure-lock byte (cl[7:0] = 00hex), configures the dio as an asynchronous serial input for calibration and test purposes. communication protocol the dio serial interface is used for asynchronous serial data communications between the max1452 and a host calibration test system or computer. the max1452 automatically detects the baud rate of the host comput- er when the host transmits the initialization sequence. baud rates between 4800bps and 38,400bps can be detected and used regardless of the internal oscillator frequency setting. data format is always 1 start bit, 8 data bits, 1 stop bit and no parity. communications are only allowed when secure-lock is disabled (i.e., cl[7:0] = 00hex) or the unlock pin is held high. initialization sequence sending the initialization sequence shown below enables the max1452 to establish the baud rate that initializes the serial port. the initialization sequence is one byte transmission of 01hex, as follows: 11111111 0 10000000 1 1111111 the first start bit 0 initiates the baud rate synchronization sequence. the 8 data bits 01hex (lsb first) follow this and then the stop bit, which is indicated above as a 1 , terminates the baud rate synchronization sequence. this initialization sequence on dio should occur after a period of 1ms after stable power is applied to the device. this allows time for the power-on-reset function to complete and the dio pin to be configured by secure-lock or the unlock pin. reinitialization sequence the max1452 allows for relearning the baud rate. the reinitialization sequence is one byte transmission of ffhex, as follows: 11111111 0 11111111 1 11111111 when a serial reinitialization sequence is received, the receive logic resets itself to its power-up state and waits for the initialization sequence. the initialization sequence must follow the reinitialization sequence in order to re-establish the baud rate. serial interface command format all communication commands into the max1452 follow a defined format utilizing an interface register set (irs). the irs is an 8-bit command that contains both an interface register set data (irsd) nibble (4-bit) and an interface register set address (irsa) nibble (4-bit). all internal calibration registers and eeprom locations are accessed for read and write through this interface reg- ister set. the irs byte command is structured as fol- lows: irs[7:0] = irsd[3:0], irsa[3:0] where: irsa[3:0] is the 4-bit interface register set address and indicates which register receives the data nib- ble irsd[3:0]. irsa[0] is the first bit on the serial interface after the start bit. irsd[3:0] is the 4-bit interface register set data. irsd[0] is the fifth bit received on the serial inter- face after the start bit. the irs address decoding is shown in table 10. special command sequences a special command register to internal logic (cril[3:0]) causes execution of special command sequences within the max1452. these command sequences are listed as cril command codes as shown in table 11. write examples a 16-bit write to any of the internal calibration registers is performed as follows: 1) write the 16 data bits to dhr[15:0] using four byte accesses into the interface register set. 2) write the address of the target internal calibration register to icra[3:0]. low-cost precision sensor signal conditioner 12 ______________________________________________________________________________________
3) write the load internal calibration register (ldicr) command to cril[3:0]. when a ldicr command is issued to the cril register, the calibration register loaded depends on the address in the internal calibration register address (icra). table 12 specifies which calibration register is decoded. erasing and writing the eeprom the internal eeprom needs to be erased (bytes set to ffhex) prior to programming the desired contents. remember to save the 3 msbs of byte 161hex (high- byte of the configuration register) and restore it when programming its contents to prevent modification of the trimmed oscillator frequency. the internal eeprom can be entirely erased with the erase command, or partially erased with the pageerase command (see table 11, cril command). it is necessary to wait 6ms after issuing the erase or pageerase command. after the eeprom bytes have been erased (value of every byte = ffhex), the user can program its contents, following the procedure below: 1) write the 8 data bits to dhr[7:0] using two byte accesses into the interface register set. 2) write the address of the target internal eeprom location to ieea[9:0] using three byte accesses into the interface register set. 3) write the eeprom write command (eepw) to cril[3:0]. serial digital output when a rdirs command is written to cril[3:0], dio is configured as a digital output and the contents of the register designated by irsp[3:0] are sent out as a byte framed by a start bit and a stop bit. once the tester finishes sending the rdirs command, it must three-state its connection to dio to allow the max1452 to drive the dio line. the max1452 three- states dio high for 1 byte time and then drive with the start bit in the next bit period followed by the data byte and stop bit. the sequence is shown in figure 5. the data returned on a rdirs command depends on the address in irsp. table 13 defines what is returned for the various addresses. multiplexed analog output when a rdalg command is written to cril[3:0] the analog signal designated by aloc[3:0] is asserted on the out pin. the duration of the analog signal is deter- mined by atim[3:0] after which the pin reverts to three- state. while the analog signal is asserted in the out pin, dio is simultaneously three-stated, enabling a par- allel wiring of dio and out. when dio and out are connected in parallel, the host computer or calibration system must three-state its connection to dio after asserting the stop bit. do not load the out line when reading internal signals, such as bdr, fsotc...etc. the analog output sequence with dio and out is shown in figure 6. the duration of the analog signal is controlled by atim[3:0] as given in table 14. max1452 low-cost precision sensor signal conditioner ______________________________________________________________________________________ 13 driven by tester driven by max1452 three-state need weak pullup three-state need weak pullup start-bit lsb start-bit lsb msb stop-bit msb stop-bit 11111 0 1 0 0 11 0 1 0 1 11111111 1000001000 1 11111111 11 dio figure 5. dio output data format
max1452 the analog signal driven onto the out pin is deter- mined by the value in the aloc register. the signals are specified in table 15. test system configuration the max1452 is designed to support an automated production test system with integrated calibration and temperature compensation. figure 7 shows the imple- mentation concept for a low-cost test system capable of testing many transducer modules connected in par- allel. the max1452 allows for a high degree of flexibili- ty in system calibration design. this is achieved by use of single-wire digital communication and three-state output nodes. depending upon specific calibration requirements one may connect all the outs in parallel or connect dio and out on each individual module. sensor compensation overview compensation requires an examination of the sensor performance over the operating pressure and tempera- ture range. use a minimum of two test pressures (e.g., zero and full-span) and two temperatures. more test pressures and temperatures result in greater accuracy. a typical compensation procedure can be summarized as follows: set reference temperature (e.g., +25c): initialize each transducer by loading their respec- tive registers with default coefficients (e.g., based on mean values of offset, fso and bridge resis- tance) to prevent overload of the max1452. set the initial bridge voltage (with the fsodac) to half of the supply voltage. measure the bridge volt- age using the bdr or out pins, or calculate based on measurements. calibrate the output offset and fso of the transduc- er using the odac and fsodac, respectively. store calibration data in the test computer or max1452 eeprom user memory. set next test temperature: calibrate offset and fso using the odac and fso- dac, respectively. store calibration data in the test computer or max1452 eeprom user memory. calculate the correction coefficients. download correction coefficients to eeprom. perform a final test. sensor calibration and compensation example the max1452 temperature compensation design cor- rects both sensor and ic temperature errors. this enables the max1452 to provide temperature compen- sation approaching the inherent repeatability of the sensor. an example of the max1452? capabilities is shown in figure 8. a repeatable piezoresistive sensor with an initial offset of 16.4mv and a span of 55.8mv was converted into a compensated transducer (utilizing the piezoresistive sensor with the max1452) with an offset of 0.5000v and a span of 4.0000v. nonlinear sensor offset and fso temperature errors, which were on the order of 20% to 30% fso, were reduced to under ?.1% fso. the fol- lowing graphs show the output of the uncompensated sensor and the output of the compensated transducer. six temperature points were used to obtain this result. 14 ______________________________________________________________________________________ driven by tester three-state need weak pullup three-state need weak pullup start-bit lsb msb stop-bit 11111 0 1 0 0 11 0 1 0 1 1111111 11111111 11 1111 111 11 1 11 three-state 2 atim +1 byte times dio out valid out high impedance figure 6. analog output timing low-cost precision sensor signal conditioner
max1452 max1452 evaluation kit to expedite the development of max1452 based transducers and test systems, maxim has pro- duced the max1452 evaluation kit (ev kit). first-time users of the max1452 are strongly encouraged to use this kit. the ev kit is designed to facilitate manual program- ming of the max1452 with a sensor. it includes the fol- lowing: 1) evaluation board with or without a silicon pressure sensor, ready for customer evaluation. 2) design/applications manual, which describes in detail the architecture and functionality of the max1452. this manual was developed for test engineers familiar with data acquisition of sensor data and provides sensor compensation algorithms and test procedures. 3) max1452 communication software, which enables programming of the max1452 from a computer keyboard (ibm compatible), one module at a time. 4) interface adapter, which allows the connection of the evaluation board to a pc serial port. low-cost precision sensor signal conditioner ______________________________________________________________________________________ 15 max1452 v out v dd module 1 data data v ss v ss v dd v dd v ss test oven max1452 v out module 2 v out digital multiplexer +5v dio[1:n] dio1 dio2 dion max1452 v out module n dvm figure 7. automated test system concept
table 2. registers register description config configuration register odac offset dac register otcdac offset temperature coefficient dac register fsodac full span output dac register fsotcdac full span output temperature coefficient dac register max1452 low-cost precision sensor signal conditioner 16 ______________________________________________________________________________________ 80 60 0 6 40 040 20 60 80 100 raw sensor output t a = +25 c pressure (kps) v out (mv) 0 1.0 3.0 2.0 4.0 5.0 040 20 60 80 100 compensated transducer t a = +25 c pressure (kps) v out (v) -20.0 10.0 30.0 20.0 -10.0 0.0 uncompensated sensor temperature error temperature ( c) error (% fso) -50 50 0 100 150 fso offset -0.15 -0.05 -0.1 0.05 0 0.1 0.15 -50 50 0 100 150 compensated transducer error temperature ( c) error (% fso) fso offset figure 8. comparison of an uncalibrated sensor and a calibrated transducer
max1452 table 3. configuration register (config[15:0]) field name description 15:13 osc[2:0] oscillator frequency setting. factory preset, do not change. 12 r ext logic ??selects external r isrc and r stc . 11 clk1m en logic ??enables clk1m output driver. 10 pga sign logic ??inverts inm and inp polarity. 9 iro sign logic ??for positive input referred offset (iro). logic ??for negative input referred offset (iro). 8:6 iro[2:0] input referred coarse offset adjustment. 5:2 pga[3:0] programmable gain amplifier setting. 1 odac sign logic ??for positive offset dac output. logic ??for negative offset dac output. 0 otcdac sign logic ??for positive offset tc dac output. logic ??for negative offset tc dac output. low-cost precision sensor signal conditioner ______________________________________________________________________________________ 17 table 4. input referred offset (iro[2:0]) iro sign, iro[2:0] input referred offset correction as % of vdd i n pu t r ef er r ed o f f set , co r r ec t io n a t vd d = 5 vd c i n mv 1,111 +1.25 +63 1,110 +1.08 +54 1,101 +0.90 +45 1,100 +0.72 +36 1,011 +0.54 +27 1,010 +0.36 +18 1,001 +0.18 +9 1,000 0 0 0,000 0 0 0,001 -0.18 -9 0,010 -0.36 -18 0,011 -0.54 -27 0,100 -0.72 -36 0,101 -0.90 -45 0,110 -1.08 -54 0,111 -1.25 -63
max1452 low-cost precision sensor signal conditioner 18 ______________________________________________________________________________________ table 8. eeprom odac and fsodac lookup table memory map temp-index[7:0] eeprom address odac low byte and high byte eeprom address fsodac low byte and high byte 00hex to 7fhex 000hex and 001hex to 0fehex and 0ffhex 200hex and 201hex to 2fehex and 2ffhex 80hex to afhex 100hex and 101hex to 15ehex and 15fhex 1a0hex and 1a1hex to 1fehex and 1ffhex table 5. pga gain setting (pga[3:0]) pga[3:0] pga gain (v/v) 0000 39 0001 52 0010 65 0011 78 0100 91 0101 104 0110 117 0111 130 1000 143 1001 156 1010 169 1011 182 1100 195 1101 208 1110 221 1111 234 table 6. temp-index typical values temp-index[7:0] temperature (?) decimal hexadecimal -40 20 14 25 65 41 85 106 6a 125 134 86 table 7. oscillator frequency setting osc[2:0] oscillator frequency 100 -37.5% 101 -28.1% 110 -18.8% 111 -9.4% 000 1mhz (nominal) 001 +9.4% 010 +18.8% 011 +28.1%
max1452 low-cost precision sensor signal conditioner ______________________________________________________________________________________ 19 table 9. control location (cl[15:0]) field name description 15:8 cl[15:8] reserved 7:0 cl[7:0] control location. secure-lock is activated by setting this to ffhex which disables dio serial communications and connects out to pga output. table 10. irsa decoding irsa[3:0] description 0000 write irsd[3:0] to dhr[3:0] (data hold register) 0001 write irsd[3:0] to dhr[7:4] (data hold register) 0010 write irsd[3:0] to dhr[11:8] (data hold register) 0011 write irsd[3:0] to dhr[15:12] (data hold register) 0100 reserved 0101 reserved 0110 write irsd[3:0] to icra[3:0] or ieea[3:0], (internal calibration register address or internal eeprom address nibble 0) 0111 write irsd[3:0] to ieea[7:4] (internal eeprom address, nibble 1) 1000 write irsd[3:0] to irsp[3:0] or ieea[9:8], (interface register set pointer where irsp[1:0] is ieea[9:8]) 1001 write irsd[3:0] to cril[3:0] (command register to internal logic) 1010 write irsd[3:0] to atim[3:0] (analog timeout value on read) 1011 write irsd[3:0] to aloc[3:0] (analog location) 1100 to 1110 reserved 1111 write irsd[3:0] = 1111bin to relearn the baud rate
max1452 low-cost precision sensor signal conditioner 20 ______________________________________________________________________________________ table 11. cril command codes cril[3:0] name description 0000 ldicr load internal calibration register at address given in icra with data from dhr[15:0]. 0001 eepw eeprom write of 8 data bits from dhr[7:0] to address location pointed by ieea[9:0]. 0010 erase erase all of eeprom (all bytes equal ffhex). 0011 rdicr read internal calibration register as pointed to by icra and load data into dhr[15:0]. 0100 rdeep read internal eeprom location and load data into dhr[7:0] pointed by ieea[9:0]. 0101 rdirs read interface register set pointer irsp[3:0]. see table 13. 0110 rdalg output the multiplexed analog signal onto out. the analog location is specified in aloc[3:0] (table 15) and the duration (in byte times) that the signal is asserted onto the pin is specified in atim[3:0] (table 14). 0111 pageerase erases the page of the eeprom as pointed by ieea[9:6]. there are 64 bytes per page and thus 12 pages in the eeprom. 1000 to 1111 reserved reserved. table 12. icra[3:0] decode icra[3:0] name description 0000 config configuration register 0001 odac offset dac register 0010 otcdac offset temperature coefficient dac register 0011 fsodac full scale output dac register 0100 fs o tc d ac full scale output temperature coefficient dac register 0101 reserved. do not write to this location (eeprom test). 0110 to 1111 reserved. do not write to this location.
max1452 low-cost precision sensor signal conditioner ______________________________________________________________________________________ 21 table 14. atim definition atim[3:0] duration of analog signal specified in byte times (8-bit time) 0000 2 0 + 1 = 2 byte times i.e. (2 ? 8)/baud rate 0001 2 1 + 1 = 3 byte times 0010 2 2 + 1 = 5 byte times 0011 2 3 + 1 = 9 byte times 0100 2 4 + 1 = 17 byte times 0101 2 5 + 1 = 33 byte times 0110 2 6 + 1 = 65 byte times 0111 2 7 + 1 = 129 byte times 1000 2 8 + 1 = 257 byte times 1001 2 9 + 1 = 513 byte times 1010 2 10 + 1 = 1025 byte times 1011 2 11 + 1 = 2049 byte times 1100 2 12 + 1 = 4097 byte times 1101 2 13 + 1 = 8193 byte times 1110 2 14 + 1 = 16,385 byte times 1111 in this mode out is continuous, however dio accepts commands after 32,769 byte times. do not parallel connect dio to out. table 13. irsp decode irsp[3:0] returned value 0000 dhr[7:0] 0001 dhr[15:8] 0010 ieea[7:4], icra[3:0] concatenated 0011 cril[3:0], irsp[3:0] concatenated 0100 aloc[3:0], atim[3:0] concatenated 0101 ieea[7:0] eeprom address byte 0110 ieed[7:0] eeprom data byte 0111 temp-index[7:0] 1000 bitclock[7:0] 1001 reserved. internal flash test data. 1010-1111 11001010 (cahex). this can be used to test communication.
max1452 low-cost precision sensor signal conditioner 22 ______________________________________________________________________________________ table 15. aloc definition aloc[3:0] analog signal description 0000 out pga output 0001 bdr bridge drive 0010 isrc bridge drive current setting 0011 vdd internal positive supply 0100 vss internal ground 0101 bias5u internal test node 0110 agnd internal analog ground. approximately half of vdd. 0111 fsodac full scale output dac 1000 fsotcdac full scale output tc dac 1001 odac offset dac 1010 otcdac offset tc dac 1011 vref bandgap reference voltage (nominally 1.25v) 1100 vptatp internal test node 1101 vptatm internal test node 1110 inp sensor? positive input 1111 inm sensor? negative input table 16. effects of compensation typical uncompensated input (sensor) typical compensated transducer output offset?... 100% fso fso??.4 to 60mv/v offset tc?..20% fso offset tc nonlinearity?.?4% fso fsotc..?.-20% fso fsotc nonlinearity?...?5% fso temperature range..??..-40 c to +125 c out...?.rati om etr i c to v d d at 5.0v offset at +25 c??.500v 200 v fso at +25 c ...4.000v 200 v offset accuracy over temp. range? 4mv ( 0.1% fso) fso accuracy over temp. range 4mv ( 0.1% fso)
max1452 low-cost precision sensor signal conditioner ______________________________________________________________________________________ 23 v dd v dd v ss v ss ? eeprom (lookup plus configuration data) v dd v ss v dd v ss fso dac unlock v dd 16-bit 16-bit 8-bit lookup address bandgap temp sensor pga mux mux fsotc register isrc r stc 75k r isrc 75k bdr fsotc inp inm fsotc dac v ss eeprom address 15eh + 15fh 000h + 001h : offset dac lookup table (176 ? 16-bits) configuration register shadow usage 19eh + 19fh 16ch + 16dh : user storage (52 bytes) 2feh + 2ffh 1a0h + 1a1h : fso dac lookup table (176 ? 16-bits) 160h + 161h reserved 162h + 163h offset tc register shadow 164h + 165h reserved 166h + 167h fsotc register shadow 168h + 169h control location register 16ah + 16bh offset dac 1 1 ? 26 phase reversal mux out amp- ampout amp+ pga gain 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 9.0 8.5 pga (3:0) 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1111 1110 total gain 39 52 65 78 91 104 117 130 143 156 169 182 195 208 234 221 iro (3, 2:0) offset mv 63 54 45 36 27 18 9 0 0 -9 -18 -27 -36 -45 -63 -54 1,111 1,110 1,101 1,100 1,011 1,010 1,001 1,000 0,000 0,001 0,010 0,011 0,100 0,101 0,111 0,110 v ss 16-bit offset tc dac otc register input referred offset (coarse offset) programmable gain stage uncommitted op amp value v ss to v dd 20mv v ss , v dd 0.01v v ss , v dd 0.25v 10mhz typical parameter i/p range i/p offset o/p range no load 1ma load unity gbw pga bandwidth 3khz 10% 16-bit *input referred offset value is proportional to v dd . values given are for v dd = 5v. v ss pga bandwidth 3khz 10% v ss test clk1m v ddf dio digital interface detailed block diagram
max1452 low-cost precision sensor signal conditioner 24 ______________________________________________________________________________________ chip information substrate connected to: v ss pin configurations 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 isrc fsotc amp+ amp- ampout clk1m dio unlock v ddf top view max1452 ssop/tssop out v ss inp inm bdr v dd test 23 24 22 21 8 79 n.c. test v ddf unlock 10 v dd n.c. fsotc n.c. n.c. amp+ 1 2 + + inm 4 5 6 17 18 16 14 13 bdr inp n.c. clk1m dio n.c. max1452 n.c. n.c. 3 15 v ss 20 11 ampout out 19 12 amp- isrc tqfn package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages . package type package code document no. 16 ssop a16-2 21-0056 16 tssop u16-2 21-0066 24 tqfn-ep t2444-4 21-0188
maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ____________________ 25 2009 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. low-cost precision sensor signal conditioner max1452 revision history revision number revision date description pages changed 2 4/09 added tqfn and tssop package information, changed packages to lead free, changed all occurrences of asic to max1452, changed v ddf rc filter values, recommended a more suitable voltage reference for non-ratiometric application circuits, corrected max1452 input range, and added typical eeprom current requirements to ec table, and added gain nonlinearity graph. 1?, 9, 10, 12, 18, 22, 24

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