STMICROELECTRONICS L497B

L497
HALL EFFECT PICKUP IGNITION CONTROLLER
.
.
.
.
..
.
..
DIRECT DRIVING OF THE EXTERNAL
POWER DARLINGTON
COIL CURRENT CHARGING ANGLE (dwell)
CONTROL
PROGRAMME COIL CURRENT PEAK LIMITATION
PROGRAMMABLE DWELL RECOVERY TIME
WHEN 94 % NOMINAL CURRENT NOT
REACHED
RPM OUTPUT
PERMANENT CONDUCTION PROTECTION
OVERVOLTAGE PROTECTION FOR EXTERNAL DARLINGTON
INTERNAL SUPPLY ZENER
REVERSE BATTERY PROTECTION
DESCRIPTION
The L497is an integratedelectronicignition controller for breakerless ignition systemsusing Hall effect
sensors.
DIP16
SO16
ORDERING NUMBERS : L497B (DIP16)
L497D1 (SO16)
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.
BLOCK DIAGRAM
March 1998
1/11
L497
ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
I3
D.C. Supply current
Transient Supply Current (tf fall time constant = 100ms)
Value
Unit
200
800
mA
mA
V3
Supply Voltage
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
15
35
mA
mA
VR
Tj, Tstg
Ptot
Int. Limited to Vz3
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
– 16
V
– 55 to 150
°C
1.2
0.65
W
W
Value
Unit
90
50
°C/W
°C/W
PIN CONNECTION (top view)
THERMAL DATA
Symbol
Parameter
Thermal Resistance Junction-ambient for DIP-16
Rth j-amb
R th j-alumin (*) Thermal Resistance Junction-alumina for SO-16
Max
Max
(* ) 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.
2/11
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 R5 limits the current through the zener for
high supply voltages.
4
N.C.
5
HALL-EFFECT INPUT
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
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
9
MAX CONDUCTION
TIME
10
DWELL CONTROL
TIMER
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 KΩ) and Csrc is the delay
capacitor at pin 8 (in µF).
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 KΩ) and CP is the delay
capacitor at pin 9 (in µF).
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 = CW; 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 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
L497
PIN FUNCTIONS (continued)
N°
Name
Function
14
DRIVER EMITTER
OUTPUT
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 KΩ 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 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
R3/R 2 defines the limitation value given by :
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
Parameter
V3
Min Op. Voltage
I3
Supply Current
Test Conditions
Typ.
Max.
Unit
5
7
18
25
13
mA
mA
28
V
7.5
8.2
V
0.6
V
V
– 50
0.5
0.9
µA
V
V
3.5
V3 = 6 V
V3 = 4 V
VS
Voltage Supply
VZ3
Supply Clamping Zener Voltage
IZ3 = 70 mA
6.8
V5
Input Voltage
Low Status
High Status
2.5
Input Current
V5 = LOW
V16–14
Darlington Driver Sat. Current
I14 = 50 mA
I14 = 180 mA
VSENS
I5
V
– 400
Current Limit. Sensing Voltage
VS = 6 to 16 V
260
320
370
mV
I11C
CW Charge Current
VS = 5.3 to 16V
V11 = 0.5V
T = 10 to 33ms
– 11.0
– 9.3
– 7.8
µA
I11D
CW Charge Current
VS = 5.3 to 16V
V11 = 0.5V
T = 10 to 33ms
0.5
0.7
1.0
µA
VS = 5.3 to 16V
V11 = 0.5V
T = 10 to 33ms
7.8
I11C / I11D
ISRC
ISENSE
Percentage of Output Current
Determining the Slow Recovery
Control Start (fig. 2), note 1
22.0
See Note 1
90
94
98.5
%
TSRC
Duration of Altered Small Contr. CSRC = 1 µF
Ratio after SRC Function Start R7 = 62 KΩ
(fig. 2)
VZ15
External Darlington over V Prot. I15 = 5 mA
Zener Voltage
I15 = 2 mA
19
18
22.5
21.5
26
25
V
V
Permanent Conduction Time
0.4
1.1
1.8
s
TP
4/11
Min.
V5 = High
CP = 1µF
R7 = 62KΩ
0.8
s
L497
ELECTRICAL CHARACTERISTICS (continued)
Symbol
Parameter
V 6SAT
RPM Output Saturation Voltage
I6 leak
Test Conditions
RPM Output Leakage Current
VS = 20 V
VZ7
Auxiliary Zener Voltage
I7 = 20 mA
V12
Reference Voltage
N otes : 1.
Min.
Typ.
I6 = 18.5 mA
I6 = 25 mA
19
1.20
1.25
Max.
Unit
0.5
0.8
V
V
50
27
µA
V
1.30
V
td
1
=
T 1 + I11C ⁄ I11D
2. Isense = Icoil when the external Darlington is in the active region.
td/t desaturation ratio is given by:
APPLICATION INFORMATION
Figure 1 : Main Waveforms.
5/11
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
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.
6/11
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 KΩ) and
Csrc the capacitor at pin 8 (in µF).
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 µF).
7/11
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 net-
Figure 4 : Application Circuit.
8/11
work 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.
L497
DIP16 PACKAGE MECHANICAL DATA
mm
DIM.
MIN.
a1
0.51
B
0.77
TYP.
inch
MAX.
MIN.
TYP.
MAX.
0.020
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
Z
3.3
0.130
1.27
0.050
9/11
L497
SO16 PACKAGE MECHANICAL DATA
mm
DIM.
MIN.
TYP.
A
a1
inch
MAX.
TYP.
1.75
0.1
MAX.
0.069
0.2
a2
0.004
0.008
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
S
10/11
MIN.
0.62
0.024
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.
11/11