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general description the MAX9921 provides a single chip solution to interface two 2-wire hall-effect sensors to a low-voltage micro- processor (?). this device supplies and monitors the cur- rent drawn by two hall-effect sensors, filters the sensed current level, and outputs the corresponding logic level. the MAX9921 includes input diagnostics and fault pro- tection. these features allow the device to determine fault conditions such as open inputs, inputs shorted to the bat- tery, and inputs shorted to ground. if the MAX9921 detects any of these conditions at either in1 or in2, the device shuts off the current to the corresponding input. the MAX9921 protects the hall sensors from supply tran- sients up to 60v at the bat supply. normal operating supply voltage ranges from 6v to 18v. if the battery volt- age is out of range, the MAX9921 shuts off the current to the hall sensors. the MAX9921 provides an 80? blanking time following hall sensor power-up or restart. the open-drain logic outputs are compatible with logic levels up to 5.5v. the MAX9921 is available in a small 10-pin ?ax package and is specified over the -40? to +125? automotive temperature range. applications features ? withstands 60v at bat supply and hall inputs ? 6v to 18v operating voltage range ? provides supply current and interfaces to two 2-wire hall sensors ? error output with diagnostics of hall inputs and bat voltage ? protects hall sensors from overvoltage by isolating them from supply transients ? hall inputs protected from short to ground ? ramps current to hall sensors at 4ma/? ? output enable input allows multiplexing of outputs from multiple MAX9921s ? hall output filtering ? hall sensor blanking following hall sensor power-up and restart ? low-power shutdown, controlled with oe and diag inputs ? operates with ?v ground shifts between hall sensor and MAX9921 MAX9921 dual, 2-wire hall-effect sensor interface with diagnostics ________________________________________________________________ maxim integrated products 1 part temp range pin-package MAX9921aub+t -40? to +125? 10 ?ax ordering information n remote ground iset battery oe err diag out1 out2 bat r iset = 63.4k , 1% v bat : 6v to 18v operating, withstands 60v 3.3v to 5v in1 0.1 f 10k in2 ref generation, diagnostics and overvoltage detect s n remote ground s 0.01 f control filter filter p/logic circuit gnd v cc 0.01 f gnd MAX9921 e c u c o n n e c t o r typical application circuit 19-4119; rev 0; 6/08 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. + denotes a lead-free package. t = tape and reel. ?ax is a registered trademark of maxim integrated products, inc. pin configuration appears at end of data sheet. door modules window lifters seat movers electric sunroofs powered lift gate controllers powered running boards seatbelt buckles
MAX9921 dual, 2-wire hall-effect sensor interface with diagnostics 2 _______________________________________________________________________________________ absolute maximum ratings dc electrical characteristics (v bat = 13.6v, v diag = 0v, v oe = 5v, in1 = in2 = no connection, r iset = 63.4k , r pu = 10k at err , out1 and out2, t a = -40? to +125?, unless otherwise noted. typical values are at t a = +25?.) (note 1) 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. bat to gnd............................................................-0.3v to +60v iset to bat ...........................................................-2.0v to +0.3v in1, in2 to gnd..........-5.0v to the lower of +60v or (v bat + 1v) diag, oe to gnd..................................................-0.3v to +6.0v out1, out2, err to gnd....................................-0.3v to +6.0v short-circuit duration of out1, out2, err to gnd or to 5.5v (individually)............................................continuous current into any pin except in1, in2 ...............................?0ma current into in1, in2.......................................................?00ma continuous power dissipation (t a = +70?) 10-pin ?ax (derate 5.6mw/? above +70?) .........444.4mw operating temperature range .........................-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 bat supply range v bat 618v v bat low for err output active v bl 5.2 v v bat high for err output active v bh 22 v i bat normal mode 1 1.3 ma bat supply current i sd shutdown mode, v oe = v diag = 0v 1 a hall inputs (in1 and in2) input current for output high i ih -11.5 ma input current for output low i il -7.2 ma input current hysteresis for high/low detection i in,hys 0.76 ma input pullup impedance r pu v bat = 6v, inputs in1, in2 with i in = -14ma 50 input voltage interpreted as shorted to battery v sb measured with respect to v bat 100 mv current range interpreted as open circuit i oc -2 +0.02 ma current level interpreted as shorted sensor to ground i sc not a sustained condition, reverts to -50? when detected -23 ma
MAX9921 dual, 2-wire hall-effect sensor interface with diagnostics _______________________________________________________________________________________ 3 note 1: all dc specifications are 100% tested at t a = +25?. ac specifications and specifications over -40? to +125? are guar- anteed by design. note 2: c l is external load capacitance on the outputs for test only. note 3: these blanking times apply when the MAX9921 is operating in normal mode. blanking times following power-up or startup from shutdown mode are 20? longer. ac timing characteristics (v bat = 13.6v, v diag = 0v, v oe = 5v, in1 = in2 = no connection, r iset = 63.4k , r pu = 10k at err , out1 and out2, t a = -40? to +125?, unless otherwise noted. typical values are at t a = +25?.) (notes 1 and 2) dc electrical characteristics (continued) (v bat = 13.6v, v diag = 0v, v oe = 5v, in1 = in2 = no connection, r iset = 63.4k , r pu = 10k at err , out1 and out2, t a = -40? to +125?, unless otherwise noted. typical values are at t a = +25?.) (note 1) parameter symbol conditions min typ max units in1, in2 blanking time at hall switch power-up t bl i ih = -11.5ma to gnd, time from v in_ = 500mv until out_ high, c l = 20pf (note 3) 50 140 ? in1, in2 current ramp rate after turn-on t ramp v in = gnd 3.8 ma/? delay from in_ to out_ (filter delay) t del from i ih to i il or from i il to i ih , c l = 20pf, figure 1 6.5 ? delay from in_ fault to err t err from i il to i sc or from i ih to i oc, falling edge only, c l = 20pf, figure 1 31 ns delay from diag high to out_ and err t dlh rising edge of diag to falling or rising edge of outputs, c l = 20pf, figure 1 350 ns delay from diag low to out_ and err t dhl falling edge of diag to falling or rising edge of outputs, c l = 20pf, figure 1 1.6 ? delay difference between rising and falling edges for both channels t dm c hall-bypass = 0.01?, i ih = -11.5ma and i il = -7.2ma, c l = 20pf 20 ns delay difference between channels t cc c hall-bypass = 0.01?, i ih = -11.5ma and i il = -7.2ma, c l = 20pf 100 ns maximum frequency on hall inputs f max c hall-bypass = 0.01?, i ih = -11.5ma and i il = -7.2ma, c l = 20pf 50 khz in_ pulse length rejected by filter to out_ p r figure 2 5.5 ? parameter symbol conditions min typ max units logic i/o (out1, out2, err , diag, and oe) output voltage low ( err , out1, out2) v ol sink current = 1ma 0.4 v three-state output current ( err , out1, out2) i oz v oe = 0v, 0 v out_ 5v ? ? input-voltage high (diag, oe) v ih 2.1 v input-voltage low (diag, oe) v il 0.8 v input resistance to gnd (diag, oe) r in 50 80 k
MAX9921 dual, 2-wire hall-effect sensor interface with diagnostics 4 _______________________________________________________________________________________ timing diagrams 14ma 7ma 0ma 5v 0v 5v 0v 5v 0v 5v 0v hall sensor open circuit short circuit 4ma/ s t del approx. 50 ma retry t err t err in 1 out1 out2 err diag figure 1. timing diagram
MAX9921 dual, 2-wire hall-effect sensor interface with diagnostics _______________________________________________________________________________________ 5 timing diagrams (continued) 14ma p r in_ out_ 0ma 7ma 5v 0v p r t del t del figure 2. hall input pulse rejection
MAX9921 dual, 2-wire hall-effect sensor interface with diagnostics 6 _______________________________________________________________________________________ typical operating characteristics (v bat = 14v, t a = +25?, unless otherwise noted.) bat supply current vs. v bat in operating mode bat voltage (v) bat current (ma) MAX9921 toc01 19.0 19.5 20.0 20.5 21.0 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 t a = -40 c bat supply current vs. v bat in operating mode bat voltage (v) bat current (ma) MAX9921 toc02 19.0 19.5 20.0 20.5 21.0 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 t a = +25 c bat supply current vs. v bat in operating mode bat voltage (v) bat current (ma) MAX9921 toc03 19.0 19.5 20.0 20.5 21.0 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 t a = +125 c bat supply current vs. v bat in operating mode bat voltage (v) bat current (ma) MAX9921 toc04 5 1015202530354045505560 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 t a = -40 c hall inputs disabled operating mode bat supply current vs. v bat in operating mode bat voltage (v) bat current (ma) MAX9921 toc05 5 1015202530354045505560 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 t a = +25 c hall inputs disabled operating mode bat supply current vs. v bat in operating mode bat voltage (v) bat current (ma) MAX9921 toc06 5 1015202530354045505560 0.6 0.8 1.0 1.2 1.4 1.6 hall inputs disabled operating mode t a = +125 c bat supply current vs. v bat in shutdown mode bat voltage (v) bat current (na) MAX9921 toc07 0 10203040 0 5 10 15 20 25 30 35 40 45 50 t a = +25 c t a = +125 c t a = -40 c hall input current hysteresis for high/low thresholds vs. temperature temperature ( c) hall input current (ma) MAX9921 toc08 -40 -25 -10 5 20 35 50 65 80 95 110 125 8.4 8.6 8.8 9.0 9.2 9.4 9.6 9.8 10.0 low threshold high threshold hall input current hysteresis for high/low threshold vs. v bat bat voltage (v) hall input current (ma) MAX9921 toc09 6 8 10 12 14 16 18 8.6 8.8 9.0 9.2 9.4 9.6 9.8 low threshold high threshold
MAX9921 dual, 2-wire hall-effect sensor interface with diagnostics _______________________________________________________________________________________ 7 typical operating characteristics (continued) (v bat = 14v, t a = +25?, unless otherwise noted.) in_ blanking time at hall switch power-up vs. temperature temperature ( c) in_ blanking time ( s) MAX9921 toc10 -40 -25 -10 5 20 35 50 65 80 95 110 125 60 65 70 75 80 85 90 95 100 in_ current ramp rate after turn-on vs. temperature temperature ( c) in_ current ramp rate (ma/ s) MAX9921 toc11 -40 -25 -10 5 20 35 50 65 80 95 110 125 0 1 2 3 4 5 delay from in_ to out_ (filter delay) vs. temperature temperature ( c) delay ( s) MAX9921 toc12 -40 -25 -10 5 20 35 50 65 80 95 110 125 5 6 7 8 9 10 delay from in_ fault to err (filter delay) vs. temperature temperature ( c) delay ( s) MAX9921 toc13 -40 -25 -10 5 20 35 50 65 80 95 110 125 0 10 20 30 40 50 delay difference between rising and falling edges for both channels vs. temperature temperature ( c) delay difference (ns) MAX9921 toc14 -40 -25 -10 5 20 35 50 65 80 95 110 125 0 20 40 60 80 100 120 140 160 180 in1 and in2 delay difference between channels vs. temperature temperature ( c) delay difference (ns) MAX9921 toc15 -40 -25 -10 5 20 35 50 65 80 95 110 125 0 50 100 150 200 250 maximum frequency on hall inputs vs. temperature temperature ( c) frequency (khz) MAX9921 toc16 -40 -25 -10 5 20 35 50 65 80 95 110 125 50 55 60 65 70 75 80 85 90 95 100 in1 and in2, 50% duty cycle in_ pulse length rejected by filter to out_ vs. temperature temperature ( c) pulse length ( s) MAX9921 toc17 -40 -25 -10 5 20 35 50 65 80 95 110 125 0 1 2 3 4 5 6 7 in1 and in2 with negative pulse in1 and in2 with positive pulse v bat undervoltage threshold vs. temperature temperature ( c) v bat threshold (v) MAX9921 toc18 -40 -25 -10 5 20 35 50 65 80 95 110 125 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6.0 6.1 6.2 v bat rising, err goes high v bat falling, err goes low
MAX9921 dual, 2-wire hall-effect sensor interface with diagnostics 8 _______________________________________________________________________________________ typical operating characteristics (continued) (v bat = 14v, t a = +25?, unless otherwise noted.) v bat overvoltage threshold vs. temperature temperature ( c) v bat threshold (v) MAX9921 toc19 -40 -25 -10 5 20 35 50 65 80 95 110 125 19.5 19.6 19.7 19.8 19.9 20.0 20.1 20.2 20.3 20.4 20.5 v bat falling, err goes low v bat rising, err goes high input pullup resistance vs. v bat v bat (v) input pullup resistance ( ) MAX9921 toc20 6 9 12 15 18 0 10 20 30 40 50 60 70 80 t a = +125 c t a = +25 c t a = -40 c threshold current vs. iset resistor change in iset resistor (%) change in threshold current (%) MAX9921 toc21 -15 -10 -5 0 5 10 15 -15 -10 -5 0 5 10 15 hysteresis input current for output high and input current for output low response of input to short to ground MAX9921 toc22 10 s/div v in1 10v/div i in1 25ma/div 0v 0v 0a v err 5v/div startup of hall input from shutdown MAX9921 toc23 20 s/div 10v/div 5v/div 5v/div 10ma/div blanking period v in_ v out_ v oe_ i in_
MAX9921 dual, 2-wire hall-effect sensor interface with diagnostics _______________________________________________________________________________________ 9 pin description pin name function 1 bat battery power supply. connect bat to the positive supply through an external reverse-polarity diode. bypass bat to ground with a 0.1? capacitor. 2 iset current-setting input. connect a 63.4k , 1% resistor (r iset ) between bat and iset to set the standard current thresholds for hall current sensing. make no other connections to iset. all routing must have low parasitic capacitance. 3 in1 hall-effect sensor input 1. bypass in1 to bat or gnd with a 0.01? capacitor. terminate an unused input with a 1.5k resistor from in1 to gnd to prevent false error diagnostics. 4 in2 hall-effect sensor input 2. bypass in2 to bat or gnd with a 0.01? capacitor. terminate an unused input with a 1.5k resistor from in2 to gnd to prevent false error diagnostics. 5 gnd ground 6 out2 open-drain output signal 2. out2 is the signal translated from hall sensor 2. connect a 10k or larger pullup resistor to logic supply. 7 out1 open-drain output signal 1. out1 is the signal translated from hall sensor 1. connect a 10k or larger pullup resistor to logic supply. 8 err open-drain diagnostic and error output. connect a 10k or larger pullup resistor to logic supply. if diag is asserted low, a high on err indicates that there is no fault while a low on err indicates that either the battery voltage is out of range or there is a fault condition. if diag is high, err provides diagnostic information in conjunction with out1 and out2. see tables 1 and 2. if oe is low or while in shutdown, err is high impedance. 9oe output enable input. oe has an internal 80k resistor to gnd. drive oe high to enable the outputs err , out1, and out2. drive oe low to place the outputs in high impedance. if oe and diag are both low for more than 40?, the device enters shutdown and all outputs are in high impedance. while in shutdown, if either oe or diag transitions low to high, the device exits shutdown mode. 10 diag diagnostic enable input. diag has an internal 80k resistor to gnd. drive diag low for normal operation. in this mode, err , out1, and out2 provide hall sensor information. drive diag high for diagnostic operation. a high-to- low transition initiates an attempt to restart, with a blanking cycle any hall input that has been shut down. see tables 1 and 2 (diagnostic truth tables). if oe and diag are both low for more than 40?, the device enters shutdown mode with all outputs in high impedance. while in the shutdown mode, if either oe or diag transitions low to high, the device exits shutdown mode.
detailed description the MAX9921 connects two 2-wire hall-effect sensors to a low-voltage ?. this device supplies current through in1 and in2 to hall sensors and monitors the current level drawn by the hall sensors. the MAX9921 outputs a high or low logic-level to the corresponding open-drain output (out1 or out2). if the current flowing out of either in1 or in2 exceeds the high input current thresh- old, the corresponding output goes high. if the current flowing out of either in1 or in2 is lower than the low input current threshold, the corresponding output goes low. hall input diagnostic normal mode in normal mode, diag is driven low. in this case, if err is high, the outputs (out1 and out2) indicate the high or low state of the corresponding hall sensors (in1 and in2). in normal mode, a low err indicates a fault. if err is low, the outputs may be pulled low and may not indicate the high or low state of the hall sensors. this can happen during the power-up, restart, or blanking cycles of the hall inputs, or due to a fault on one or both of the hall inputs, or when v bat is out of range, while the error output is low. if one output continues signaling and the other output is low, the output with the low logic-level indicates a fault or a restart and blanking cycle on the corresponding hall input. table 1 summarizes normal mode operation. diagnostic mode when diag is driven high, the MAX9921 enters diagnos- tic mode. in this mode, out1 and out2 output diagnos- tic information. in1 takes precedence over in2. in2? diagnostics remain masked until a fault on in1 is cleared. for diagnostics and troubleshooting, when in1 or in2 shuts off due to an input short to ground, it continues to source 50?. a falling edge at diag restarts a hall input that has been shut off due to a short to ground. diagnostic indications are never latched internally and they indicate the real-time state of in1 or in2. table 2 summarizes diagnostic mode operation. hall input fault detection if a fault is detected, the err output is asserted low to notify the ?. this condition can occur due to the hall input being shorted to ground, shorted to battery, or open. MAX9921 dual, 2-wire hall-effect sensor interface with diagnostics 10 ______________________________________________________________________________________ functional diagram oe err diag out1 out2 bat in1 in2 ref generation, diagnostics, and overvoltage detect iset control filter filter gnd MAX9921 input output diag err out1 out2 diagnosis comment 0 1 0 or 1 0 or 1 out1 and out2 indicate state of in1 and in2, respectively normal mode: no fault indication (outputs indicate hall sensor high or low status) 00 0 0 fault on in1 and/or in2, or v bat out of range, or power-up or restart blanking (unknown current level of in1 and in2) normal mode: err asserted low indicates fault (outputs may no longer indicate the high or low state of the hall sensors) 0 0 0 0 or 1 fault on in1 or restart blanking of in1 normal mode: err asserted low indicates fault; hall output 2 continues signaling 0 0 0 or 1 0 fault on in2 or restart blanking of in2 normal mode: err asserted low indicates fault; hall output 1 continues signaling table 1. diagnostic truth table (normal mode)
MAX9921 dual, 2-wire hall-effect sensor interface with diagnostics ______________________________________________________________________________________ 11 hall sensor protection from supply transients if the v bat voltage is lower than 6v or exceeds 18v, in1 and in2 shut off current to both hall sensors and err , out1, and out2 go low. when v bat returns to the proper range, both in1 and in2 restart, following a blanking cycle. hall inputs open condition if either in1 or in2 is open (i in < 2ma), the correspond- ing input shuts off current to the hall sensor. if in1 or in2 is loaded, it exits the open input fault condition and restarts the corresponding hall input, following a blank- ing cycle. hall input shorted to battery if either in1 or in2 is shorted to the battery (v in > v bat + 100mv), the MAX9921 shuts off current to the corre- sponding hall sensor. in this case, if in1 or in2 is more than 1v above v bat , it may back-drive current into bat. in such a condition, the current level in the hall input should not exceed 100ma. therefore, all the MAX9921s together can share a separate reverse- polarity protection diode to avoid powering up other cir- cuitry sharing a common diode (figure 4). input output diag err out1 out2 diagnosis 1 0 0 0 no fault 1 0 0 1 in1 open circuit, or in1 open circuit and fault on in2 1 0 1 0 in1 shorted to battery, or in1 shorted to battery and fault on in2 1 0 1 1 in1 shorted to ground, or in1 shorted to ground and fault on in2 1100 v bat out of range, or power-up or restart and blanking cycle (dominant fault masks all other faults) 1 1 0 1 in2 open circuit 1 1 1 0 in2 shorted to battery 1 1 1 1 in2 shorted to ground table 2. diagnostic truth table (diagnostic mode) bat iset MAX9921 in1 in2 gnd diag oe err out1 out2 bat bat gnd other circuitry r iset battery reverse-polarity diode for MAX9921s reverse-polarity diode for other circuitry r iset iset MAX9921 in1 in2 gnd diag oe err out1 out2 figure 4. several MAX9921s connected to a common reverse-polarity diode
MAX9921 hall input short-to-ground the hall input shorted-to-ground fault is effectively a latched condition if the input remains loaded by the hall switch when the shorting condition is removed. the cur- rent required to power the hall switch is shut off and only a 50? pullup current remains. the hall input can be manually re-energized or it can be re-energized by the ecu. a falling edge at diag initiates a restart with a blanking cycle of any hall input that has been shut down due to the shorted-to-ground condition. during startup or restart, it is possible for a hall input to charge up an exter- nal capacitance of 0.02? without tripping into a shorted- to-ground latched state. all other fault conditions are not latched and when these other faults are removed, err goes high and the hall input is again functional. manual method for re-energizing hall sensor and means for diagnosing an intermittent hall sensor connection figure 5 shows the behavior of the MAX9921 when a hall input is open. figure 6 shows the behavior of the MAX9921 when the open input is reconnected to a hall sensor. figures 5 and 6 demonstrate how a shorted-to- ground hall input can be reset. resetting a shorted-to-ground hall input involves three steps: 1) relieve the short to ground at the hall sensor. 2) disconnect the hall input from the hall sensor (open input fault condition). 3) reconnect the hall input to the hall sensor. the MAX9921 restarts the hall input with a blanking cycle. if the hall input is disconnected from the hall sensor for 10ms, it allows the hall input to be pulled up by the 50? pullup current to register the open-input fault condition. then, reconnecting the hall input to the hall sensor restarts the hall input with a blanking cycle. this provides a manual means of re-energizing a hall input without having to resort to the ecu to reset it. this also demonstrates that an intermittent connection to a hall sensor can recover without intervention of the ecu. this gives the ecu a means of diagnosing an intermit- tent connection to a hall sensor by using the diagnostic mode to detect a diagnostic sequence of ?pen-circuit to ?lanking cycle?to ?o fault. dual, 2-wire hall-effect sensor interface with diagnostics 12 ______________________________________________________________________________________ 14v v in_ i in_ 0v hall input short to ground fault indicated hall input open-circuit fault indicated time v bat - 25mv 5mv/ms time 50 a 0a hall input disconnected from sensor figure 5. hall input ramps to open-circuit fault when short to ground is relieved
MAX9921 dual, 2-wire hall-effect sensor interface with diagnostics ______________________________________________________________________________________ 13 14v v in_ i in_ 0v v bat - 500mv 8v 4ma/ s 11.5ma 0a time time hall input reconnected to hall sensor figure 6. hall input re-energized when open input is reconnected to hall sensor MAX9921 actions fault description criterion err output hall input response comment/recovery v bat < 6v asserted low shutoff current to both hall sensors both in1 and in2 are restarted with blanking cycle when v bat returns to proper range. v bat > 18v asserted low shutoff current to both hall sensors both in1 and in2 are restarted with blanking cycle when v bat returns to proper range. hall input open i in < 2ma asserted low shutoff current to corresponding hall sensor when a hall input is again loaded, terminating open input condition, the hall input are restarted with blanking cycle. hall input shorted to battery v in > v bat due to external reverse-battery protection diode asserted low shutoff current to corresponding hall sensor if a hall input is pulled more than 1v above v bat , the input may back drive current into the bat supply and pull v bat up with it. in this condition, current levels in the hall inputs should never exceed 100ma. for this reason, it is recommended that one or more MAX9921s be powered together and share a reverse-polarity diode separate from other circuitry. hall input shorted to ground i in > 23ma asserted low shutoff current to corresponding hall sensor. 50? of pullup current is sourced to in1 or in2 to aid in troubleshooting. a falling edge at diag initiates a restart with a blanking cycle of any hall input that has been shut off due to a short to ground. see hall input short-to-ground description. table 3. summary of fault protection and recovery
MAX9921 dual, 2-wire hall-effect sensor interface with diagnostics 14 ______________________________________________________________________________________ applications information hall-effect sensor selection the MAX9921 is optimized for use with 2-wire hall- effect switches or with 3-wire hall-effect switches con- nected as 2-wire (figure 7). when using a 3-wire hall sensor, the resistor r is chosen so that the current drawn by the hall sensor crosses the MAX9921 current threshold when the magnetic threshold of the hall sen- sor is exceeded. table 4 shows a partial list of mostly 2-wire hall switch- es, which can be used with the MAX9921. hall input bypass capacitor the MAX9921 is optimized for use with external protec- tion 0.01? capacitors from both in1 and in2 to bat. these are essential to ensure robustness against auto- motive transients. these capacitors may be tied to gnd instead of to bat, but the connection to bat is recommended. low-voltage operation to ensure correct operation of the hall sensor at low input voltages, it is important to consider the voltage drop of the MAX9921 with low battery voltages. this dropout voltage can be calculated using the formula: v dropout = i hall x r pu i hall is the maximum current which must be supplied to the hall sensor and r pu is the internal resistance of the MAX9921, nominally 50 (see the input pullup resistance vs. v bat graph in the typical operating characteristics ). as an example, assume the use of a hal573 sensor, which draws a maximum current of 17ma. the dropout voltage is then 850mv and the approximate minimum voltage supplied to the hall sensor is 6v - 0.85v = 5.15v, which is higher than the minimum operating voltage of 3.75v specified for the hal573. MAX9921 in_ r v cc x_ gnd figure 7. 3-wire hall-effect switches configured as 2-wire part manufacturer website comment hal573-6 micronas www.micronas.com 2-wire hal556/560/566 micronas www.micronas.com 2-wire hal581/584 micronas www.micronas.com 2-wire a1140/1/2/3 allegro www.allegromicro.com 2-wire 3161 allegro www.allegromicro.com 3-wire, optimized for 2-wire use without added resistor tle4941/c infineon www.infineon.com 2-wire table 4. partial list of compatible hall switches
MAX9921 dual, 2-wire hall-effect sensor interface with diagnostics 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 ____________________ 15 2008 maxim integrated products is a registered trademark of maxim integrated products, inc. chip information process: bicmos pin configuration 1 2 3 4 5 10 9 8 7 6 diag oe err out1 in2 in1 iset bat MAX9921 max top view out2 gnd package type package code document no. 10 ?ax u10+2 21-0061 package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages .

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