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l497 july 2003 hall effect pickup ignition controller ? . direct driving of the external power darlington . coil current charging angle (dwell) control . programme coil current peak limita- tion . programmable dwell recovery time when 94 % nominal current not reached . rpm output . permanent conduction protection . overvoltage protection for exter- nal darlington . internal supply zener . reverse battery protection description the l497 is an integrated electronic ignition control- ler for breakerless ignition systems using hall effect sensors. ordering numbers : L497B (dip16) l497d1 (so16) dip16 so16 the device drives an npn external darlington to control the coil current providing the required stored energy with low dissipation. a special feature of the l497 is the programmable time for the recovery of the correct dwell ratio t d /t when the coil peak current fails to reach 94 % of the nominal value. in this way only one spark may have an energy less than 94 % of the nominal one during fast acceleration or cold starts. block diagram 1/11
absolute maximum ratings symbol parameter value unit i 3 d.c. supply current transient supply current (t f fall time constant = 100ms) 200 800 ma ma v 3 supply voltage int. limited to vz 3 v 6 rpm voltage 28 v i 16 d.c. driver collector current pulse " "(t <= 3ms) 300 600 ma ma v 16 driver collector voltage 28 v i 7 auxiliary zener current 40 ma i 15 d.c. overvoltage zener current pulse " " t fall = 300 m s, tr ep repetition time > = 3ms 15 35 ma ma v r reverse battery voltage if application circuit of fig. 4 is used C 16 v t j , t stg junction and storagetemperature range C 55 to 150 c p tot power dissipation at t aluminia = 90 c for so-16 t amb = 90 c for dip-16 1.2 0.65 w w pin connection (top view) thermal data symbol parameter value unit r th j-amb r th j-alumin (*) thermal resistance junction-ambient for dip-16 thermal resistance junction-alumina for so-16 max max 90 50 c/w c/w (*) thermal resistance junction-aluminia with the device soldered on the middle of an aluminia supporting substrate mesuring 15 x 20 ; 0.65 mm thickness. l497 2/11
pin functions (refer to fig. 4) n name function 1 gnd this pin must be connected to ground. 2 signal gnd this pin must be connected to ground. 3 power supply supply voltage input. an internal 7.5 v (typ) zener zener limits the voltage at this pin. the external resistor r 5 limits the current through the zener for high supply voltages. 4 n.c. this pin must be connected to ground or left open. 5 hall-effect input hall-effect pickup signal input. this input is dwell control circuit output in order to enable the current driving into the coil. the spark occurs at the high-to-low transition of the hall-effect pickup signal. furthermore this input signal enables the slow recovery and permanent conduction protection circuits. the input signal, supplied by the open collector output stage of the hall effect sensor, has a duty-cycle typically about 70 %. v 5 is internally clamped to v 3 and ground by diodes 6 rpm output open collector output which is at a low level when current flows in the ignition coil. for high voltages protection of this output, connection to the pin 7 zener is recommended. in this situation r 8 must limit the zener current, too, and r 1 limits pin 6 current if rpm module pad is accidentally connected to v s . 7 aux. zener a 21 v (typ) general purpose zener. its current must be limited by an external resistor. 8 recovery time a capacitor connected between this pin and ground sets the slope of the dwell time variation as it rises from zero to the correct value. this occurs after the detection of i coll 94 % i nom , just before the low transition of the hall-effect signal pulse. the duration of the slow recovery is given by : t src = 12,9 r 7 c src (ms) where r 7 is the biasing resistor at pin 12 (in k w ) and c src is the delay capacitor at pin 8 (in m f). 9 max conduction time a capacitor connected between this pin and ground determines the intervention delay of the permanent conduction protection. after this delay time the coil current is slowly reduced to zero. delay time t p is given by : t p =16 c p r 7 (ms) where r 7 is the biasing resistor at pin 12 (in k w ) and c p is the delay capacitor at pin 9 (in m f). 10 dwell control timer a capacitor c t connected between this pin and ground is charged when the hall effect output is high and is discharged at the high to low transition of the hall effect signal. the recommended value is 100 nf using a 62 k w resistor at pin 12. 11 dwell control the average voltage on the capacitor cw connected between this pin and ground depends on the motor speed and the voltage supply. the comparison between v cw and v ct voltage determines the timing for the dwell control. for the optimized operation of the device c t = c w ; the recommended value is 100 nf using a 62 k w resistor at pin 12. 12 bias current a resistor connected between this pin and ground sets the internal current used to drive the external capacitors of the dwell control (pin 10 and 11) permanent conduction protection (pin 9) and slow recovery time (pin 8). the recommended value is 62 k w . 13 current sensing connection for the coil current limitation. the current is measured on the sensing resitor r s and taken through the divider r 10 /r 11 . the current limitation value is given by : i sens = 0.32 r 10 + r 11 r s r 11 l497 3/11
pin functions (continued) n name function 14 driver emitter output current driver for the external darlington. to ensure stability and precision of t desat c c and r 9 must be used. recommended value for r 9 is 2 k w in order not to change the open loop gain of the system. r c may be added to c c to obtain greater flexibility in various application situations. c c and r c values ranges are 1 to 100 nf and 5 to 30 k w depending on the external darlington type. 15 overvoltage limit the darlington is protected against overvoltage by means of an internal zener available at this pin and connected to pin 14. the internal divider r 3 /r 2 defines the limitation value given by : v ovp = ? ? 22.5 r 3 + 5.10 - 3 ? ? r 2 + 22.5 16 driver collector input the collector current of the internal driver which drives the external darlington is supplied through this pin. then the external resistor r 6 limits the maximum current supplied to the base of the external darlington. electrical characteristics (v s = 14.4 v, C 40 c < t j < 125 c unless otherwise specified) symbol parameter test conditions min. typ. max. unit v 3 min op. voltage 3.5 v i 3 supply current v 3 = 6 v v 3 = 4 v 5 7 18 25 13 ma ma v s voltage supply 28 v v z3 supply clamping zener voltage i z3 = 70 ma 6.8 7.5 8.2 v v 5 input voltage low status high status 2.5 0.6 v v i 5 input current v 5 = low C 400 C 50 m a v 16C14 darlington driver sat. current i 14 = 50 ma i 14 = 180 ma 0.5 0.9 v v v sens current limit. sensing voltage v s = 6 to 16 v 260 320 370 mv i 11c c w charge current v s = 5.3 to 16v v 11 = 0.5v t = 10 to 33ms C 11.0 C 9.3 C 7.8 m a i 11d cw charge current v s = 5.3 to 16v v 11 = 0.5v t = 10 to 33ms 0.5 0.7 1.0 m a i 11c / i 11d vs = 5.3 to 16v v 11 = 0.5v t = 10 to 33ms see note 1 7.8 22.0 i src i sense percentage of output current determining the slow recovery control start (fig. 2), note 1 90 94 98.5 % t src duration of altered small contr. ratio after src function start (fig. 2) c src = 1 m f r 7 = 62 k w 0.8 s v z15 external darlington over v prot. zener voltage i 15 = 5 ma i 15 = 2 ma 19 18 22.5 21.5 26 25 v v t p permanent conduction time v 5 = high c p = 1 m f r 7 = 62k w 0.4 1.1 1.8 s l497 4/11
electrical characteristics (continued) symbol parameter test conditions min. typ. max. unit v 6sat rpm output saturation voltage i 6 = 18.5 ma i 6 = 25 ma 0.5 0.8 v v i 6 leak rpm output leakage current v s = 20 v 50 m a v z7 auxiliary zener voltage i 7 = 20 ma 19 27 v v 12 reference voltage 1.20 1.25 1.30 v figure 1 : main waveforms. application information notes : 1. 2. td/t desaturation ratio is given by: td t = 1 1 + i 11c i 11d i sense = i coil when the external darlington is in the active region. l497 5/11
dwell angle control the dwell angle control circuit calculates the con- duction time d for the output transistor in relation to the speed of rotation, to the supply voltage and to the characteristics of the coil. on the negative edge of the hall-effect input signal the capacitor c w begins discharging with a constant current l 11d . when the set peak value of the coil cur- rent is reached, this capacitor charges with a con- stant current i 11c = 13.3 x i 11d , and the coil current is kept constant by desaturation of the driven stage and the external darlington. the capacitor c t starts charging on the posi- tive.edge of the hall-effect input signal with a con- stant current i 10c . the dwell angle, and conse- quently the starting point of the coil current conduc- tion, is decided by the comparison between v 10 and v 11 . a positive hysteresis is added to the dwell compa- rator to avoid spurious effects and c t is rapidly dis- charged on the negative edge of hall-effects input signal. in this way the average voltage on c w increases if the motor speed decreases and viceversa in order to maintain constant the ratio t d t at any motor speed. t d t is kept constant (and not d t = cost) to control the power dissipation and to have sufficient time to avoid low energy sparks during acceleration. desaturation times in static conditions in static conditions and if c t = c w as recommended and if the values of the application circuit of fig.4 are used. t d t = 1 1 + i 11c / i 11d desaturation times in low and high frequency operation due to the upper limit of the voltage range of pin 11, if the components of fig.4 are used, below 10 hz (300 rpm for a 4 cylinder engine) the off time reaches its maximum value (about 50 ms) and then the circuit gradually loses control of the dwell angle because d = t C 50 ms. over 200 hz (6000 rpm for a 4 cylinder engine) the available time for the conduction is less than 3.5 ms. if the used coil is 6 mh, 6a, the off time is reduced to zero and the circuit loses the dwell angle control. transient response the ignition system must deliver constant energy even during the condition of acceleration and decel- eration of the motor below 80hz/s. these conditions can be simulated by means of a signal gene-rator with a linearly modulated frequency between 1 hz and 200 hz (this corresponds to a change between 30 and 6000 rpm for a 4 cylinders engine). current limit the current in the coil is monitored by measuring the i sense current flowing in the sensing resistor r s on the emitter of the external darlington. i sense is given by : i sense = i coil + i 14 when the voltage drop across rs reaches the inter- nal comparator threshold value the feedback loop is activated and i sense kept constant (fig.1) forcing the external darlington in the active region. in this con- dition : i sense = i coil when a precise peak coil current is required r s must be trimmed or an auxiliary resistor divider (r 10 , r 11 ) added : icpeak ( a ) = 0.320 rs ) ? ? r10 r11 + 1 ? ? slow recovery control (fig. 2) if i sense has not reached 94 % of the nominal value just before the negative edge of the hall-effect input signal, the capacitor c src and c w are quickly dis- charged as long as the pick-up signal is "low". at the next positive transition of the input signal the load current starts immediately, producing the maximum achievable t desat ; then the voltage on c src in- creases linearly until the standby is reached. during this recovery time the c src voltage is converted into a current which, substrated from the charging cur- rent of the dwell capacitor, produces a t desat modu- lation. this means that the t desat decreases slowly until its value reaches, after a time t src , the nominal 7% value. the time t src is given by: t rsc = 12.9 r7 c src (ms) where r 7 is the biasing resistor at pin 12 (in k w ) and c src the capacitor at pin 8 (in m f). l497 6/11
figure 2 : src : i coil failure and time dependence of active region. figure 3 : permanent conduction protection. h j : input signal i c : coil current v cm : voltage on capacitor c src. d st : percentage of imposed desaturation time. permanent conduction protection (fig. 3) the permanent conduction protection circuit moni- tors the input period, charging cp with a costant cur- rent when the sensor signal is high and discharging it when the sensor signal is low. if the input remains high for a time longer than t p the voltage across c p reaches an internally fixed value forcing the slow de- crease of coil current to zero. a slow decrease is necessary to avoid undesired sparks. when the in- put signal goes low again c p is swiftly discharged and the current control loop operates normally. the delay time t p is given by : t p (sec) = 18 c p r 7 where r 7 is the biasing resistor on pin 12 (in k) and cp the delay capacitor at pin 9 (in m f). l497 7/11
other application notes dump protection load dump protection must be implemented by an external zener if this function is necessary. in fig. 4 dz 2 protects the driver stage, the connection be- tween pin 6 and 7 protects the output transistor of pin 6. moreover dz 1 protects both the power supply input (pin 3) and hall-effect sensor. resistor r 4 is necessary to limit dz 1 current during load dump. overvoltage limitation the external darlington collector voltage is sensed by the voltage divider r 2 , r 3 . the voltage limitation increases rising r 2 or decreasing r 3 . due to the active circuit used, an r o c o series net- work is mandatory for stability during the high vol- tage condition. r o c o values depend on the darlington used in the application. moreover the resistor r 13 is suggested to limit the overvoltage even when supply voltage is discon- nected during the high voltage condition. reverse battery protection due to the presence of external impedance at pin 6, 3, 16, 15 l497 is protected against reverse battery voltage. negative spike protection if correct operation is requested also during short negative spikes, the diode d s and capacitor c s must be used. figure 4 : application circuit. l497 8/11
dip16 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 outline and mechanical data l497 9/11
so16 narrow dim. mm inch min. typ. max. min. typ. max. a 1.75 0.069 a1 0.1 0.25 0.004 0.009 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 (1) 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 (1) 3.8 4 0.150 0.157 g 4.6 5.3 0.181 0.209 l 0.4 1.27 0.016 0.050 m 0.62 0.024 s (1) d and f do not include mold flash or protrusions. mold flash or potrusions shall not exceed 0.15mm (.006inch). outline and mechanical data 8?(max.) 0016020 weight: 0.20gr l497 10/11
information furnished is believed to be accurate and reliable. however, stmicroelectronics assumes no responsib ility for the conse- quences of use of such information nor for any infringement of patents or other rights of third parties which may result from i ts use. no license is granted by implication or otherwise under any patent or patent rights of stmicroelectronics. specification mentioned in this publication are subject to change without notice. this publication supersedes and replaces all information previously supplied. stmi- croelectronics products are not authorized for use as critical components in life support devices or systems without express wr itten approval of stmicroelectronics. the st logo is a registered trademark of stmicroelectronics ? 2003 stmicroelectronics C printed in italy C all rights reserved stmicroelectronics group of companies australia - brazil - canada - china - finland - france - germany - hong kong - india - israel - italy - japan - malaysia - malt a - morocco - singapore - spain - sweden - switzerland - united kingdom - united states. http://www.st.com l497 11/11

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