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L497
HALL EFFECT PICKUP IGNITION CONTROLLER
.DI .COI .PROGRAMMECOI .PROGRAMMABLEDWELLRECOVERYTI .RPMOUTPUT .PERMANENTCONDUCTI .OVERVOLTAGEPROTECTI .I .REVERSEBATTERYPROTECTI
NAL DARLINGTON NTERNAL SUPPLY ZENER ON BLOCK DIAGRAM
RECT DRIVING OF THE EXTERNAL POWER DARLINGTON L CURRENT CHARGING ANGLE (dwell) CONTROL L CURRENT PEAK LIMITATION ME WHEN 94 % NOMINAL CURRENT NOT REACHED ON PROTECTION ON FOR EXTER-
DIP16
SO16
ORDERING NUMBERS : L497B (DIP16) L497D1 (SO16)
DESCRIPTION The L497is an integratedelectronicignition controller for breakerless ignition systemsusing Hall effect sensors.
The device drives an NPN external darlington to control the coil current providingthe required stored energy with low dissipation. A special feature of the L497 is the programmable time for the recovery of the correct dwell ratio Td/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.
March 1998
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L497
ABSOLUTE MAXIMUM RATINGS
Symbol I3 V3 V6 I16 V16 I7 I15 Parameter D.C. Supply current Transient Supply Current (tf fall time constant = 100ms) Supply Voltage RPM Voltage D.C. Driver Collector Current Pulse " "(t <= 3ms) Driver Collector Voltage Auxiliary Zener Current D.C. Overvoltage Zener Current Pulse " " t fall = 300s, trep Repetition Time > = 3ms Reverse Battery Voltage if Application Circuit of Fig. 4 is used Junction and StorageTemperature Range Power Dissipation at Taluminia = 90 C for SO-16 Tamb = 90 C for DIP-16 Value 200 800 Int. Limited to Vz3 28 300 600 28 40 15 35 - 16 - 55 to 150 1.2 0.65 V mA mA V mA mA mA V C W W Unit mA mA
VR Tj, Tstg Ptot
PIN CONNECTION (top view)
THERMAL DATA
Symbol Parameter Max Max Value 90 50 Unit C/W C/W
Thermal Resistance Junction-ambient for DIP-16 Rth j-amb R th j-alumin (*) Thermal Resistance Junction-alumina for SO-16
(* ) Thermal resistance junction-aluminia wi th the device soldered on the mi ddle of an aluminia supporting substrate mesuri ng 15 x 20 ; 0.65 mm thickness.
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L497
PIN FUNCTIONS (refer to fig. 4)
N 1 2 3 Name GND SIGNAL GND POWER SUPPLY Function This pin must be connected to ground. This pin must be connected to ground. Supply Voltage Input. An internal 7.5 V (typ) zener zener limits the voltage at this pin. The external resistor R5 limits the current through the zener for high supply voltages. This pin must be connected to ground or left open. 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 %. V5 is internally clamped to V3 and ground by diodes 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 R1 limits pin 6 current if RPM module pad is accidentally connected to VS. A 21 V (typ) General Purpose Zener. Its current must be limited by an external resistor. 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 Icoll 94 % Inom, just before the low transition of the hall-effect signal pulse. The duration of the slow recovery is given by : tsrc = 12,9 R7 Csrc (ms) where R7 is the biasing resistor at pin 12 (in K) and Csrc is the delay capacitor at pin 8 (in F). 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 Tp is given by : Tp =16 Cp R7 (ms) where R7 is the biasing resistor at pin 12 (in K) and CP is the delay capacitor at pin 9 (in F). A capacitor CT 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 resistor at pin 12. 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 VCW and VCT voltage determines the timing for the dwell control. For the optimized operation of the device CT = CW; the recommended value is 100 nF using a 62 K resistor at pin 12. 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. Connection for the Coil Current Limitation. The current is measured on the sensing resitor RS and taken through the divider R 10/R 11. The current limitation value is given by : Isens = 0.32 R 10 + R11 RS R11 3/11
4 5
N.C. HALL-EFFECT INPUT
6
RPM OUTPUT
7 8
AUX. ZENER RECOVERY TIME
9
MAX CONDUCTION TIME
10
DWELL CONTROL TIMER
11
DWELL CONTROL
12
BIAS CURRENT
13
CURRENT SENSING
L497
PIN FUNCTIONS (continued)
N 14 Name DRIVER EMITTER OUTPUT Function Current Driver for the External Darlington. To ensure stability and precision of Tdesat Cc and R9 must be used. Recommended value for R9 is 2 K in order not to change the open loop gain of the system. Rc may be added to Cc to obtain greater flexibility in various application situations. Cc and Rc values ranges are 1 to 100 nF and 5 to 30 K depending on the external darlington type. The darlington is protected against overvoltage by means of an internal zener available at this pin and connected to pin 14. The internal divider R3/R 2 defines the limitation value given by :
15
OVERVOLTAGE LIMIT
22.5 + 5.10-3 R + 22.5 Vovp = 2 R3
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 R6 limits the maximum current supplied to the base of the external darlington.
ELECTRICAL CHARACTERISTICS (VS = 14.4 V, - 40 C < Tj < 125 C unless otherwise specified)
Symbol V3 I3 VS VZ3 V5 I5 V16-14 VSENS I11C Parameter Min Op. Voltage Supply Current Voltage Supply Supply Clamping Zener Voltage Input Voltage Input Current Darlington Driver Sat. Current Current Limit. Sensing Voltage CW Charge Current IZ3 = 70 mA Low Status High Status V5 = LOW I14 = 50 mA I14 = 180 mA VS = 6 to 16 V VS = 5.3 to 16V V11 = 0.5V T = 10 to 33ms VS = 5.3 to 16V V11 = 0.5V T = 10 to 33ms VS = 5.3 to 16V V11 = 0.5V T = 10 to 33ms Percentage of Output Current Determining the Slow Recovery Control Start (fig. 2), note 1 Duration of Altered Small Contr. CSRC = 1 F Ratio after SRC Function Start R7 = 62 K (fig. 2) External Darlington over V Prot. I15 = 5 mA Zener Voltage I15 = 2 mA Permanent Conduction Time V5 = High CP = 1F R7 = 62K 19 18 0.4 260 - 11.0 320 - 9.3 6.8 2.5 - 400 - 50 0.5 0.9 370 - 7.8 7.5 V3 = 6 V V3 = 4 V Test Conditions Min. 3.5 5 7 18 25 13 28 8.2 0.6 Typ. Max. Unit V mA mA V V V V A V V mV A
I11D
CW Charge Current
0.5
0.7
1.0
A
I11C / I11D
7.8 See Note 1 90 94
22.0
ISRC ISENSE TSRC
98.5
%
0.8
s
VZ15 TP
22.5 21.5 1.1
26 25 1.8
V V s
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L497
ELECTRICAL CHARACTERISTICS (continued)
Symbol V 6SAT I6 leak VZ7 V12
N otes : 1.
Parameter RPM Output Saturation Voltage RPM Output Leakage Current Auxiliary Zener Voltage Reference Voltage
td/t desaturation ratio is given by:
Test Conditions I6 = 18.5 mA I6 = 25 mA VS = 20 V I7 = 20 mA
Min.
Typ.
Max. 0.5 0.8 50
Unit V V A V V
19 1.20 1.25
27 1.30
td 1 = T 1 + I11C I11D 2. Isense = Icoil when the external Darlington is in the active region.
APPLICATION INFORMATION Figure 1 : Main Waveforms.
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L497
DWELL ANGLE CONTROL The dwell angle control circuit calculates the conduction 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 capacitorCW beginsdischargingwith a constant current l11D. Whenthe set peak value of the coil current is reached, this capacitor charges with a constant current I11C = 13.3 x I11D, and the coil current is kept constant by desaturationof the driven stage and the external darlington. The capacitor CT starts charging on the positive.edge of the Hall-effect input signal with a constant current I10C. The dwell angle, and consequentlythe starting point of the coil current conduction, is decided by the comparison between V10 and V11. A positive hysteresis is added to the dwell comparator to avoid spurious effects and CT is rapidly discharged on the negative edge of Hall-effects input signal. In this way the average voltage on CW increases if the motor speed decreases and viceversa in order td to maintainconstantthe ratio at any motor speed. T td D is kept constant (and not = cost) to control T T 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 CT = CW as recommended and if the values of the applicationcircuit of fig.4 are used. td 1 = T 1 + I11C / I11D TRANSIENT RESPONSE The ignition system must deliver constant energy even duringthe conditionof accelerationand decelerationof the motor below80Hz/s.Theseconditions 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 currentin thecoil is monitoredby measuringthe Isense current flowing in the sensing resistor Rs on the emitter of the external darlington. Isense is given by : I sense = Icoi l + I 14 When the voltage drop across Rs reaches the internal comparator thresholdvalue the feedbackloop is activated and Isense kept constant (fig.1) forcing the external darlington in the active region. In this condition : I sense = I coil Whena precisepeak coil currentis requiredRs must be trimmed or an auxiliary resistor divider (R10, R11) added : 0.320 R10 + 1 Ic p eak(A) = RS) R11 SLOW RECOVERY CONTROL (fig. 2) If Isense has not reached 94 % of the nominal value just before the negativeedge of the Hall-effect input signal, the capacitor Csrc and CW are quickly dischargedas long as the pick-up signalis "low". At the next positive transition of the input signal the load current starts immediately, producingthe maximum achievable Tdesat; then the voltage on CSRC increases linearly until the standby is reached.During this recoverytime the CSRC voltageis convertedinto a current which, substrated from the charging current of the dwell capacitor, produces a Tdesat modulation. This means that the Tdesat decreases slowly until its valuereaches,after a time TSRC, thenominal 7% value. The time TSRC is given by: Trsc = 12.9 R7 CSRC (ms) where R7 isthe biasing resistor at pin 12 (in K) and Csrc the capacitor at pin 8 (in F).
DESATURATION TIMES IN LOW AND HIGH FREQUENCY OPERATION Due to the upperlimit of the voltagerange of pin 11, if the components of fig.4 are used, below 10 Hz (300 RPM for a 4 cylinder engine) the OFF time reachesits maximum value (about 50 ms) and then the circuit gradually loses control of the dwell angle because D = T - 50 ms. Over 200 Hz (6000 RPM for a 4 cylinderengine) the availabletime for the conductionis 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.
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L497
Figure 2 : SRC : Icoil Failure and Time Dependence of Active Region.
HJ : Input signal IC : Coil current
VCM : Voltage on capacitor CSRC. DST : Percentage of imposed desaturation time.
Figure 3 : Permanent Conduction Protection.
PERMANENT CONDUCTION PROTECTION (fig. 3) The permanent conduction protection circuit monitors the input period, chargingCP with a costantcurrent 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 TP the voltage across CP reachesan internallyfixed valueforcingthe slow decrease of coil current to zero. A slow decrease is
necessary to avoid undesired sparks. When the input signal goes low again CP is swiftly discharged and the current control loop operates normally. The delay time TP is given by : T P (sec) = 18 CP R7 Where R7 is the biasing resistor on pin 12 (in K) and Cp the delay capacitor at pin 9 (in F).
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L497
OTHER APPLICATION NOTES DUMP PROTECTION Load dump protection must be implemented by an external zener if this function is necessary. In fig. 4 DZ2 protects the driver stage, the connection between pin 6 and 7 protects the output transistor of pin 6. MoreoverDZ1 protectsboth the power supply input (pin 3) and Hall-effect sensor. Resistor R4 is necessary to limit DZ1 current during load dump. OVERVOLTAGE LIMITATION The external darlington collector voltage is sensed by the voltage divider R2, R3. The voltage limitation increases rising R2 or decreasing R3. Due to the active circuit used, an Ro Co series network is mandatory for stability during the high voltage condition. Ro Co values depend on the darlington used in the application. Moreover the resistor R13 is suggested to limit the overvoltage even when supply voltage is disconnected during the high voltage condition. REVERSE BATTERY PROTECTION Due to the presenceof externalimpedanceat pin 6, 3, 16, 15 L497 is protected against reverse battery voltage. NEGATIVE SPIKE PROTECTION If correct operation is requested also during short negativespikes,the diode DS and capacitorCs must be used.
Figure 4 : Application Circuit.
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L497
DIP16 PACKAGE MECHANICAL DATA
DIM. MIN. a1 B b b1 D E e e3 F I L Z 3.3 1.27 8.5 2.54 17.78 7.1 5.1 0.130 0.050 0.51 0.77 0.5 0.25 20 0.335 0.100 0.700 0.280 0.201 1.65 mm TYP. MAX. MIN. 0.020 0.030 0.020 0.010 0.787 0.065 inch TYP. MAX.
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L497
SO16 PACKAGE MECHANICAL DATA
DIM. MIN. A a1 a2 b b1 C c1 D E e e3 F L M S 3.8 0.5 9.8 5.8 1.27 8.89 4.0 1.27 0.62 8 (max.) 0.150 0.020 10 6.2 0.35 0.19 0.5 45 (typ.) 0.386 0.228 0.050 0.350 0.157 0.050 0.024 0.394 0.244 0.1 mm TYP. MAX. 1.75 0.2 1.6 0.46 0.25 0.014 0.007 0.020 0.004 MIN. inch TYP. MAX. 0.069 0.008 0.063 0.018 0.010
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L497
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 infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specification mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously 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 Microelectronics. (c) 1998 SGS-THOMSON Microelectronics - Printed in Italy - All Rights Reserved SGS-THOMSON Microelectronics GROUP OF COMPANIES Australia - Brazil - Canada - China - France - Germany - Italy - Japan - Korea - Malaysia - Malta - Morocco - The Netherlands Singapore - Spain - Sweden - Switzerland - Taiwan - Thailand - United Kingdom - U.S.A.
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