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L484 november 1991 magnetic pickup ignition controller . direct driving of the external dar- lington . operates with a wide range of ma- gnetic pickup types . charging angle (dwell) control . coil current peak limitation . continuous coil current protection . tachometer signal output . external darlington overvoltage protection . load dump and reverse battery pro- tection . possibility of spark point delaying (anti knock system) description the L484 is an integrated circuit designed for use with an npn darlington in breakerless ignition sy- stems with magnetic pickup sensors and high ener- gy ignition coils. a key feature of the L484 is flexibility. it can be used with a wide variety of magnetic sensors thanks to the special design which has two input pins from the pic- kup ; the first is the zero crossing detector for the ignition command and the second pin is used to cal- culate the dwell time. moreover another pin is used to adapt the L484 to various pickup types. other features of the device include darlington over- voltage protection, dump protection, a supply volt- age range of 6-28 v. dip16 ordering numbers : L484 (dip16) L484d1 (so16) so16 block diagram 1/11
absolute maximum ratings symbol parameter value unit v r reverse battery voltage C 14 v v d dump voltage 100 v p tot power dissipation at t amb = 90 c0.75w t j , t stg junction and storage temperature range C 55 to 150 c thermal data symbol parameter value unit r th j-amb thermal resistance junction-ambient ( dip16 ) max 80 c/w r th j-al thermal resistance junction-alumina ( so16 ) max 50 c/w pin connection L484 2/11
pin functions (refer to fig. 2) n name function 1 current sensing input connection for coil current limitation. the current is measured on the sense resistor r sens and divided on r1/r2. the current limitation value is given by : i sens = r1 + r2 r sens r2 2 pickup input magnetic pickup signal input. this pin sets the dwell time, i.e. the max negative pickup voltage value starting from which the device can drive the current into the coil. the real dwell time will be a function of the dwell control logic. increasing the resistor r11 the maximum conduction time increases. the max input current foreseen is 2ma. 3 permanent conduct. protection timer a capacitor c1 connected between this pin and ground sets the delay of the permanent conduction protection in the coil current. using a 50nf capacitor the typical desaturation time delay for the protection is 75ms. 4 permanent conduct. protection inhibit a low level on this input (max 0.7v) disables the protection, irrespective of the state of pin 3. if the protection is used this pin must be left open. 5 rpm output open collector output signal which is at a low level when the final darlington is in on status. the current is internally limited at 10ma. 6 dwell time adjust at high motor rotation speeds, i.e. when the peak value of the magnetic pick-up signal exceedes 6v using r12 = 100k w , this pin may be used to vary the dwell ratio. adding a resistor in series r a between this pin and pin 11 the desaturation time is reduced. it is therefore possible to use this pin to adapt the L484 to various pickup types. the maximum value of the resistor r a is 200k w . 7 dwell control timer a capacitor c2 connected between this pin and ground sets the timing for the dwell control. the recommended value is 100nf. the resistors r b /r c provide an hysteresis to confirm on state and avoid spurious sparks. 8 zero crossing input zero cross detector input of the magnetic pickup signal for the ignition actuation. at high motor rotation speeds, the external resistor r12 may be used to vary the desaturation time ratio, to adapt the L484 to various signal waveforms of time magnetic pick-up. reducing the resistor value the dwell time increases. typically the range of values for resistor r12 is from 50k w to 150k w .. 9 power-on input a low level on this pin forces the external darlington into conduction particularly useful in anti knock system. this function is particularly useful in antiknock system because provides a spark time delay. anyway the current limitation, the permanent conduction protection and the dump protection are operating even when pin 9 is at a low level. if this function is not used it must be left open. 10 signal ground this pin must be connected to ground. 11 power supply supply voltage input. a 7v (typ) zener is present at the input. the external resistor r9 limits the current through the zener for higher supply voltages. 12 dump protection the device is protected against the load dump. in load dump condition an internal circuit, based on a zener diode and a darlington transistor, switches off the external darlington and short circuits the supply. by means of the external divider r8/r9 the protection threshold can be changed and is given as first approximation by: v dth = 8.5 ? ? r8 + r9 r9 ? ? + 5 10 - 4 r8 (the resistor r9 value must be higher than 4k w ). 13 power ground this pin must be connected to ground. * this function is particularly useful in antiknock systeme because provides a spark time delay. anyway the c urrent limitation, the pemanent con duction protection and the dump protection are operating even when pin 9 is at a low level. L484 3/11
pin functions (continued) n name function 14 driver collector input the collector current for the internal driver which drives the external darlington is supplied through this pin. the external resistor r10 limits the dissipation in the ic. the value this resistor depends on the darlington used and on the limiting current in the coil. 15 overvoltage limitation the external darlington is protected against overvoltage by means of an internal zener available at this pin. the external divider r5/r6 defines the limitation value, typically given by : v ovp = ? ? 30 r5 + 5 10 - 3 ? ? r6 + 30 16 driving stage output current driver for the external darlington. to ensure stability on the current limitation loop a capacitor c3 (typically 2.2nf, this value depending on the darlington used) must be connected between this pin and the current sensing input (pin 1). electrical characteristics (v s = 14.4v ; t j = - 40 to 125 c unless otherwise specified ; referred to the test circuit) symbol parameter test conditions min. typ. max. unit v s operating supply voltage 6 28 v v is input stage voltage (pin 2 with 10k w resistor) 160 200 240 mv v th on pick-up thresh. voltage at low rpm (pin 2) v is C30 v is +30 mv v sens current limitation sensing voltage (pin 1) v s = 6 to 16v 200 320 mv v zc zero crossing thresh. voltage (pin 8) 3 20 60 mv v h hysteresis voltage (pin 8) 100 200 mv i 7c i 7d i 7d /i 7c c d well charge current c d well discharge current at low rpm v pick-up = 0.5v ; or pin 6 not connected (*) note 1 0.7 7 7 3 30 15 m a m a i 7c i 7d i 7d /i 7c c d well charge current c d well discharge current at high rpm v pick-up = 9v (**) note 2 8 13 0.7 33 44 3.2 m a m a v pin3 i 3 threshold voltage output current t amb = 25 c (***) note 3 0.85 4 3 v m a v cp continuous coil current protection inhibit low voltage (pin 4). 0 0.7 v v cesat series darlington driver saturation voltage (v pin 14 - 16 ) i pin14 = 150ma i pin14 = 50ma 0.4 1 0.6 v v v z zener volt. pin 11 i pin11 = 140ma 6.5 8.8 v v ovz external darlington overvoltage protection zener voltage t amb = 25 c ; i pin15 = 5 to 15ma 25 35 v i 09 pin 9 output current in low status v 9 = 0v 3 ma v ch i ch tachometer signal output low voltage. (pin5) output leakage (pin 5) on condition i sink = 0.5ma off condition v pin5 = 5v 0.7 10 v m a L484 4/11
dump protection symbol paramater test conditions min. typ. max. unit v dz zener dump (pin 12) i pin12 = 2ma 7.5 9.5 v (*) note 1 : td/t is given by the formula : td 1 = t 1 + i7d/i7c (**) note 2 : td k = t 1 + i7d/i7c k value depends on the pickCup used in the application ; typically k = 0.1 (***) note 3 : the permanent conduction protection is guaranteed over the full temperature range circuit operation the L484 controls the charging angle (dwell) and the peak value of the primary current in the coil over the full range of operating conditions. the coil current is limited to a predetermined level by means of a negative feedback circuit including a current sensing resistor, a comparator, the driver stage and the power switch. the dwell control circuit keeps the output stage in its active region during current limitation. the time the output stage is operating in the active region (desa- turation time), is sufficient to compensate for possi- ble variation in the energy stored due to the acceleration of the motor ; moreover this time is li- mited to avoid excessive power dissipation. magnetic pickCup characteristics the typical magnetic pickup waveforms are shown in fig. 1, the amplitude of the signal being a function of the frequency. however on the market there are many types of magnetic pickup, of which the wave- forms may differ very much. adjusting the value of the resistor r 11 on pin 2 and/or adding a resistor r a between the pin 6 (dwell adjust) and pin 11, as shown in the application circuit, it is possible to adapt the L484 to a wide range of magnetic pickup wave- forms. particularly by means of the resistor r 11 on pin 2 it is possible to define the maximum advance of the conduction start into the coil . this is very useful at high pickCup frequency. control of the dwell angle the dwell angle control circuit defines the conduc- tion time of the output darlington, versus the speed of rotation, the supply voltage and the charac- teristics of the coil. in each cycle the time the transistor operates in the active region is compared with a reference time and the error signal amplified to advance or delay the conduction in the next cycle. to limit the power dis- sipation the desaturation time is typically fixed to 10% of the period t. at very low frequencies the on thershold is fixed at 200mv of the input signal and the desaturation time is mainly determined by the peak waveform. this positive threshold also prevents permanent conduc- tion when the motor is stopped. when the input fre- quency increases the dwell control gradually sets the desaturation time to 10% of the period. at higher frequencies the on threshold becomes negative to permit a conduction angle of more than 50% always keeping desaturation time to 10% of the period. current limiting the current in the coil is measured by means of a voltage drop across a suitable resistor in the emitter lead of the power transistor. when the threshold voltage (260mv typ) is reached, the coil current is kept constant via a feedback loop. L484 5/11
darlington overvoltage limitation the darlington is protected against overvoltage by means of an external divider r 5 /r 6 (pin 15) and an internal zener. this zener drives the external darlin- gton in order to limit the collector voltage. charging angle signal output this signal is intended for tachometer applications (pin 5). it consists of an open collector stage with current internally limited at 10ma "power on" signal input in the low status this input forces the external dar- lington into conduction (pin 9). this control input can be used together with the conduction time informa- tion coming from pin 5 to bypass the normal dwell time calculation. when an external logic control is used to recognize particular engine condition (as in anti knock system). protection circuits permanent conduction protection this function is intended to prevent continuous cur- rent conduction in the final stage when the magnetic pickup is open or intermittent. the duration of the in- tervention is set by means of a capacitor 1 at pin 3. grounding pins 3 or 4, this protection is eliminated. the inhibit function at pin 4 is particularly useful when an external logic control is used to disable the permanent conduction protection. reverse battery and dump protection due to the external resistors r 6 , r 7 , r 8 , r 10 the de- vice is protected against reverse battery. the load dump protection withstands up to 100v with a decay time 300ms. the intervention threshold for load dump is fixed by means of an external divider con- nected to pin 11. other application information if the supply is voltage disconnected - or the battery wire is broken - while the current is flowing through the coil, the external diode d 1 keeps the coil current from recirculating into the device : in this way both device and darlington are protected. the zener diode dz, connected between pin 14 and gnd, allows to withstand positive spikes up to 200v. the device - used in the recommended application circuit - satisfies the iso/dp 7637/1 overvoltage standard. figure 1 : typical magnetic pickCup waveform and L484 response at low and high fequency. L484 6/11
figure 1 : typical magnetic pick-up waveform and L484 response at low and high frequency (continued). L484 7/11
figure 2 : application circuit. L484 8/11
dip16 package mechanical data dim. mm inch min. typ. max. min. typ. max. a1 0.51 0.020 b 0.77 1.65 0.030 0.065 b 0.5 0.020 b1 0.25 0.010 d 20 0.787 e 8.5 0.335 e 2.54 0.100 e3 17.78 0.700 f 7.1 0.280 i 5.1 0.201 l 3.3 0.130 z 1.27 0.050 L484 9/11
so16 package mechanical data dim. mm inch min. typ. max. min. typ. max. a 1.75 0.069 a1 0.1 0.2 0.004 0.008 a2 1.6 0.063 b 0.35 0.46 0.014 0.018 b1 0.19 0.25 0.007 0.010 c 0.5 0.020 c1 45 (typ.) d 9.8 10 0.386 0.394 e 5.8 6.2 0.228 0.244 e 1.27 0.050 e3 8.89 0.350 f 3.8 4.0 0.150 0.157 l 0.5 1.27 0.020 0.050 m 0.62 0.024 s8 (max.) L484 10/11
information furnished is believed to be accurate and reliable. however, sgs-thomson microelectronics assumes no responsibility for the consequences of use of such information nor for any inf ringement of patents or other rights of third part ies which may result from its use. no license is granted by impl ication or otherwise under any pat ent or patent rights of sgs-thomson microelectronics. specifica- tions mentioned in t his publication are subject to change without noti ce. this publication supersedes and replaces all information pre- viously supplied. sgs-thomson microelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of sgs-thomson microelec tronics. ? 1994 sgs-thomson microelectronics - all rights reserved sgs-thomson microelectronics group of companies aust ralia - brazil - france - germany - hong kong - i taly - j apan - korea - malaysia - malta - morocco - the netherlands - sin gapore - spain - sweden - switzerland - taiwan - thaliand - united k ingdom - u.s.a. L484 11/11

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