L497 STMICROELECTRONICS | Alldatasheet
Document overview
- Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
- PDF pages: 11
Technical content
HALL EFFECT PICKUP IGNITION CONTROLLER .DIRECT DRIVING OF THE EXTERNAL POWER DARLINGTON .COIL CURRENT CHARGING ANGLE (dwell) CONTROL .PROGRAMMECOIL CURRENT PEAKLIMITA- 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 L497is an integratedelectronicignition control - ler for breakerless ignition systemsusing Hall effect sensors. ORDERING NUMBERS : L497B (DIP16) L497D1 (SO16) DIP16 SO16 The device drives an NPN external darlington to controlthe 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 peakcurrent fails to reach 94 % of the nominal value.In this way only one spark may have an energyless than 94 % ofthe nominal one during fast accelerationor cold starts. BLOCK DIAGRAM
Symbol Parameter Value Unit I3 D.C. Supply current Transient Supply Current (tf fall time constant = 100ms) 200 800 mA mA V3 Supply Voltage Int. Limited to Vz 3 V6 RPM Voltage 28 V I16 D.C. Driver Collector Current Pulse ” ”(t <= 3ms) 300 600 mA mA V16 Driver Collector Voltage 28 V I7 Auxiliary Zener Current 40 mA I15 D.C. Overvoltage Zener Current Pulse ” ” t fall= 300µs, trep Repetition Time > = 3ms mA mA VR Reverse Battery Voltage if Application Circuit of Fig. 4 is used – 16 V Tj,T stg Junction and StorageTemperature Range – 55 to 150 °C Ptot Power Dissipation at Taluminia=9 0°C for SO-16 Tamb =9 0°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 °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
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 V3 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 R1 limits pin 6 current if RPM module pad is accidentally connected to VS . 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 Icoll≤ 94 % Inom , just before the low transition of the hall-effect signal pulse. The duration of the slow recovery is given by : t src= 12,9 R7 Csrc(ms) where R7 is the biasing resistor at pin 12 (in KΩ ) and Csrc is the delay capacitor at pin 8 (inµF).
9 MAX CONDUCTION
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 : Tp =16 Cp R7 (ms) where R7 is the biasing resistor at pin 12 (in KΩ ) and CP is the delay capacitor at pin 9 (inµF).
10 DWELL CONTROL
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 KΩ 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 VCW and VCT voltage determines the timing for the dwell control. For the optimized operation of the device CT =C W ; the recommended value is 100 nF using a 62 KΩ 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 KΩ . 13 CURRENT SENSING Connection for the Coil Current Limitation. The current is measured on the sensing resitor R S and taken through the divider R10/R11. The current limitation value is given by : Isens = 0.32⋅R 10 + R11 R S ⋅R 11 L497
PIN FUNCTIONS (continued) N ° Name Function
14 DRIVER EMITTER
Current Driver for the External Darlington. To ensure stability and precision of Tdesat C c and R9 must be used. Recommended value for R9 is 2 KΩ in order not to change the open loop gain of the system. R c may be added to Cc to obtain greater flexibility in various application situations. C c and Rc values ranges are 1 to 100 nF and 5 to 30 KΩ 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/R2 defines the limitation value given by : Vovp = 22.5 R 3 + 5.10−3 R 2 + 22.5
16 DRIVER COLLECTOR
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<T j< 125°C unless otherwise specified) Symbol Parameter Test Conditions Min. Typ. Max. Unit V3 Min Op. Voltage 3.5 V I3 Supply Current V 3 =6V V3 =4V 18 25 mA mA VS Voltage Supply 28 V VZ3 Supply Clamping Zener Voltage IZ3 = 70 mA 6.8 7.5 8.2 V V5 Input Voltage Low Status High Status 2.5 0.6 V V I5 Input Current V 5 = LOW – 400 – 50 µA V16–14 Darlington Driver Sat. Current I14 =5 0m A I14 = 180 mA 0.5 0.9 V V VSENS Current Limit. Sensing Voltage VS = 6 to 16 V 260 320 370 mV I11C C W Charge Current V S = 5.3 to 16V V11 = 0.5V T = 10 to 33ms I11D CW Charge Current V S = 5.3 to 16V V11 = 0.5V T = 10 to 33ms 0.5 0.7 1.0 µA I11C /I11D VS = 5.3 to 16V V11 = 0.5V T = 10 to 33ms See Note 1 7.8 22.0 ISRC ISENSE 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 µF R 7 =6 2K Ω 0.8 s VZ15 External Darlington over V Prot. Zener Voltage I15 =5m A I15 =2m A 22.5 21.5 V V TP Permanent Conduction Time V 5 = High C P =1 µF R 7 = 62KΩ 0.4 1.1 1.8 s L497
ELECTRICAL CHARACTERISTICS (continued) Symbol Parameter Test Conditions Min. Typ. Max. Unit V 6SAT RPM Output Saturation Voltage I6 = 18.5 mA I6 =2 5m A 0.5 0.8 V V I6 leak RPM Output Leakage Current V S =2 0V 5 0 µA VZ7 Auxiliary Zener Voltage I 7 =2 0m A 1 9 2 7 V V12 Reference Voltage 1.20 1.25 1.30 V Figure 1 :Main Waveforms.
APPLICATION INFORMATION
Notes : 1. td/t desaturation ratio is given by:td T = 1 1 + I11C ⁄I11D Isense =Icoilwhen the external Darlington is in theactive region. L497
The dwell angle control circuit calculates the con- ductiontime D for the output transistor in relation to the speed of rotation, to the supply voltage and to the characteristicsof the coil. On the negativeedge of the Hall-effect input signal the capacitorC W beginsdischargingwith a constant currentl11D. Whenthe setpeakvalue of thecoil cur- rent is reached, this capacitor charges with a con- stant current I 11C = 13.3 x I11D, and the coil current is kept constant by desaturationof 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- quentlythe starting point of the coil current conduc- tion, is decided by the comparison betweenV 10 and V11. A positive hysteresis is added to the dwell compa- rator to avoid spurious effects and CT 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 maintainconstanttheratiotd T atany motorspeed. td T is kept constant (and notD 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 staticconditionsand if CT =C W asrecommended and if the values of the applicationcircuit offig.4 are used. td T = 1 1 + I11C /I11D 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 graduallyloses control of the dwell angle because D = T – 50 ms. Over 200 Hz (6000 RPMfor a 4 cylinderengine)the availabletime forthe conductionis less than3.5 ms. If the used coilis 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 duringthe conditionof accelerationand decel- erationof the motorbelow80Hz/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 Thecurrentin thecoilis monitoredbymeasuringthe I sense current flowing in the sensing resistor Rs on the emitter of the external darlington. Isense is given by : Isense =Icoil+I 14 When the voltagedrop across Rs reaches the inter- nal comparatorthresholdvalue the feedbackloop is activated and I sense kept constant (fig.1) forcing the external darlington in the active region. In this con- dition : Isense =Icoil Whenaprecisepeakcoil currentis requiredRs must be trimmed or an auxiliary resistor divider (R10,R11) added : Icpeak(A )= 0.320 RS ) ⋅ R10 R11 + 1 SLOW RECOVERY CONTROL (fig. 2) If Isense has not reached 94 % of the nominal value just before the negativeedge of theHall-effect input signal, the capacitor Csrc and CW are quickly dis- chargedas longas the pick-up signalis ”low”. At the next positive transition of the input signal the load current startsimmediately, producingthe maximum achievable T desat; then the voltage on CSRC in- creaseslinearly until the standbyis reached.During thisrecoverytime the CSRC voltageis convertedinto a current which, substrated from the charging cur- rentof thedwell capacitor, producesa Tdesatmodu- lation. This means that the Tdesatdecreasesslowly untilitsvaluereaches,aftera timeTSRC , thenominal 7% value. The time TSRC is given by: Trsc= 12.9 R7 CSRC (ms) where R7 isthe biasingresistor at pin12 (in KΩ )and C srcthe capacitor at pin 8 (inµF). L497
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. MoreoverDZ1 protectsboth the powersupply input (pin 3) and Hall-effect sensor. Resistor R4 is necessary to limit DZ1 current during load dump. OVERVOLTAGELIMITATION 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 net- work is mandatory for stability during the high vol- tage 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 discon- nected during the high voltage condition. REVERSE BATTERY PROTECTION Dueto thepresenceof 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 diodeD S andcapacitorCs must be used. Figure 4 :ApplicationCircuit. L497
DIP16 PACKAGE MECHANICAL DATA DIM. mm inch 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 L497
SO16 PACKAGE MECHANICAL DATA DIM. mm inch 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 S 8° (max.) 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. 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. L497