® L497

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
DIP16 SO16

.. REACHED
RPM OUTPUT
ORDERING NUMBERS : L497B (DIP16)
L497D1 (SO16)

. PERMANENT CONDUCTION PROTECTION

OVERVOLTAGE PROTECTION FOR EXTER-

..
The device drives an NPN external darlington to
NAL DARLINGTON control the coil current providing the required stored
INTERNAL SUPPLY ZENER energy with low dissipation.
REVERSE BATTERY PROTECTION
A special feature of the L497 is the programmable
time for the recovery of the correct dwell ratio Td/T
DESCRIPTION when the coil peak current fails to reach 94 % of the
The L497 is an integrated electronic ignition control- nominal value. In this way only one spark may have
ler for breakerless ignition systems using Hall effect an energy less than 94 % of the nominal one during
sensors. fast acceleration or cold starts.

BLOCK DIAGRAM

July 2003 1/11

L497

ABSOLUTE MAXIMUM RATINGS

Symbol Parameter Value Unit

I3 D.C. Supply current 200 mA
Transient Supply Current (tf fall time constant = 100ms) 800 mA
V3 Supply Voltage Int. Limited to Vz3
V6 RPM Voltage 28 V
I16 D.C. Driver Collector Current 300 mA
Pulse " "(t <= 3ms) 600 mA
V16 Driver Collector Voltage 28 V
I7 Auxiliary Zener Current 40 mA
I15 D.C. Overvoltage Zener Current
Pulse " " tfall = 300µs, 15 mA
trep Repetition Time > = 3ms 35 mA
VR Reverse Battery Voltage if Application Circuit of Fig. 4 is used – 16 V
Tj, Tstg Junction and StorageTemperature Range – 55 to 150 °C
Ptot Power Dissipation
at Taluminia = 90 °C for SO-16 1.2 W
Tamb = 90 °C for DIP-16 0.65 W

PIN CONNECTION (top view)

THERMAL DATA

Symbol Parameter Value Unit

Rth j-amb Thermal Resistance Junction-ambient for DIP-16 Max 90 °C/W
Rth j-alumin (*) Thermal Resistance Junction-alumina for SO-16 Max 50 °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.

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 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. 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 %. 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 R8 must limit the zener current, too, and R1 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 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 R 7 is the biasing resistor at pin 12 (in KΩ) and Csrc is the delay
capacitor at pin 8 (in µF).
9 MAX CONDUCTION A capacitor connected between this pin and ground determines the
TIME 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).
10 DWELL CONTROL A capacitor CT connected between this pin and ground is charged when the
TIMER 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 C T = 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 R10/R11. The current
limitation value is given by :

R10 + R11
Isens = 0.32 ⋅
RS ⋅ R11

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L497

PIN FUNCTIONS (continued)

N° Name Function
14 DRIVER EMITTER Current Driver for the External Darlington. To ensure stability and precision
OUTPUT 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/R2 defines the limitation value given by :

22.5 
Vovp =  + 5.10−3  R2 + 22.5
 R3 

16 DRIVER COLLECTOR The collector current of the internal driver which drives the external
INPUT 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 (VS = 14.4 V, – 40 °C < Tj < 125 °C unless otherwise specified)

Symbol Parameter Test Conditions Min. Typ. Max. Unit

V3 Min Op. Voltage 3.5 V
I3 Supply Current V3 = 6 V 5 18 25 mA
V3 = 4 V 7 13 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 0.6 V
High Status 2.5 V
I5 Input Current V5 = LOW – 400 – 50 µA
V16–14 Darlington Driver Sat. Current I14 = 50 mA 0.5 V
I14 = 180 mA 0.9 V
VSENS Current Limit. Sensing Voltage VS = 6 to 16 V 260 320 370 mV
I11C CW Charge Current VS = 5.3 to 16V – 11.0 – 9.3 – 7.8 µA
V11 = 0.5V
T = 10 to 33ms
I11D CW Charge Current VS = 5.3 to 16V 0.5 0.7 1.0 µA
V11 = 0.5V
T = 10 to 33ms
I11C / I11D VS = 5.3 to 16V 7.8 22.0
V11 = 0.5V
T = 10 to 33ms See Note 1
ISRC Percentage of Output Current 90 94 98.5 %
ISENSE Determining the Slow Recovery
Control Start (fig. 2), note 1
TSRC Duration of Altered Small Contr. CSRC = 1 µF 0.8 s
Ratio after SRC Function Start R7 = 62 KΩ
(fig. 2)
VZ15 External Darlington over V Prot. I15 = 5 mA 19 22.5 26 V
Zener Voltage I15 = 2 mA 18 21.5 25 V
TP Permanent Conduction Time V5 = High 0.4 1.1 1.8 s
CP = 1µF
R7 = 62KΩ

4/11
 L497

ELECTRICAL CHARACTERISTICS (continued)

Symbol Parameter Test Conditions Min. Typ. Max. Unit

V6SAT RPM Output Saturation Voltage I6 = 18.5 mA 0.5 V
I6 = 25 mA 0.8 V
I6 leak RPM Output Leakage Current VS = 20 V 50 µA
VZ7 Auxiliary Zener Voltage I7 = 20 mA 19 27 V
V12 Reference Voltage 1.20 1.25 1.30 V

Notes : 1. td 1
td/t desaturation ratio is given by: =
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 TRANSIENT RESPONSE

The dwell angle control circuit calculates the con- The ignition system must deliver constant energy
duction time D for the output transistor in relation to even during the condition of acceleration and decel-
the speed of rotation, to the supply voltage and to eration of the motor below 80Hz/s. These conditions
the characteristics of the coil. can be simulated by means of a signal gene-rator
with a linearly modulated frequency between 1 Hz
On the negative edge of the Hall-effect input signal
and 200 Hz (this corresponds to a change between
the capacitor CW begins discharging with a constant
30 and 6000 RPM for a 4 cylinders engine).
current l11D. When the set peak value of the coil cur-
rent is reached, this capacitor charges with a con- CURRENT LIMIT
stant current I11C = 13.3 x I11D, and the coil current
is kept constant by desaturation of the driven stage The current in the coil is monitored by measuring the
and the external darlington. Isense current flowing in the sensing resistor Rs on
the emitter of the external darlington. Isense is given
The capacitor CT starts charging on the posi-
by :
tive.edge of the Hall-effect input signal with a con- I sense = I coil + I 14
stant current I10C. The dwell angle, and conse-
quently the starting point of the coil current conduc- When the voltage drop across Rs reaches the inter-
tion, is decided by the comparison between V10 and nal comparator threshold value the feedback loop is
V11. activated and Isense kept constant (fig.1) forcing the
A positive hysteresis is added to the dwell compa- external darlington in the active region. In this con-
dition :
rator to avoid spurious effects and CT is rapidly dis-
charged on the negative edge of Hall-effects input I sense = I coil
signal. When a precise peak coil current is required Rs must
In this way the average voltage on CW increases if be trimmed or an auxiliary resistor divider (R10, R11)
the motor speed decreases and viceversa in order added :
0.320  R10 
td Ic peak (A) = ⋅ + 1
to maintain constant the ratio at any motor speed.
T RS)  R11 
td D
is kept constant (and not = cost) to control SLOW RECOVERY CONTROL (fig. 2)
T T
the power dissipation and to have sufficient time to If Isense has not reached 94 % of the nominal value
avoid low energy sparks during acceleration. just before the negative edge of the Hall-effect input
signal, the capacitor Csrc and CW are quickly dis-
DESATURATION TIMES IN STATIC charged as long as the pick-up signal is "low". At the
CONDITIONS next positive transition of the input signal the load
In static conditions and if CT = CW as recommended current starts immediately, producing the maximum
and if the values of the application circuit of fig.4 are achievable Tdesat; then the voltage on CSRC in-
used. creases linearly until the standby is reached. During
td 1 this recovery time the CSRC voltage is converted into
= a current which, substrated from the charging cur-
T 1 + I11C / I11D
rent of the dwell capacitor, produces a Tdesat modu-
lation. This means that the Tdesat decreases slowly
until its value reaches, after a time TSRC, the nominal
DESATURATION TIMES IN LOW AND HIGH 7% value.
FREQUENCY OPERATION
The time TSRC is given by:
Due to the upper limit of the voltage range of pin 11,
if the components of fig.4 are used, below 10 Hz Trsc = 12.9 R7 CSRC (ms)
(300 RPM for a 4 cylinder engine) the OFF time where R7 is the biasing resistor at pin 12 (in KΩ) and
reaches its maximum value (about 50 ms) and then Csrc the capacitor at pin 8 (in µF).
the circuit gradually loses control of the dwell angle
because D = T – 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.

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 L497

Figure 2 : SRC : Icoil Failure and Time Dependence of Active Region.

HJ : Input signal VCM : Voltage on capacitor CSRC.

IC : Coil current DST : Percentage of imposed desaturation time.

Figure 3 : Permanent Conduction Protection.

PERMANENT CONDUCTION PROTECTION necessary to avoid undesired sparks. When the in-
(fig. 3) put signal goes low again CP is swiftly discharged
The permanent conduction protection circuit moni- and the current control loop operates normally.
tors the input period, charging CP with a costant cur- The delay time TP is given by :
rent when the sensor signal is high and discharging T P (sec) = 18 C P R 7
it when the sensor signal is low. If the input remains Where R7 is the biasing resistor on pin 12 (in K) and
high for a time longer than TP the voltage across CP Cp the delay capacitor at pin 9 (in µF).
reaches an internally fixed value forcing the slow de-
crease of coil current to zero. A slow decrease is

7/11
L497

OTHER APPLICATION NOTES

DUMP PROTECTION work is mandatory for stability during the high vol-
Load dump protection must be implemented by an tage condition.
external zener if this function is necessary. In fig. 4 Ro Co values depend on the darlington used in the
DZ2 protects the driver stage, the connection be- application.
tween pin 6 and 7 protects the output transistor of Moreover the resistor R13 is suggested to limit the
pin 6. Moreover DZ1 protects both the power supply overvoltage even when supply voltage is discon-
input (pin 3) and Hall-effect sensor. nected during the high voltage condition.
Resistor R4 is necessary to limit DZ1 current during
load dump. REVERSE BATTERY PROTECTION
Due to the presence of external impedance at pin 6,
OVERVOLTAGE LIMITATION 3, 16, 15 L497 is protected against reverse battery
The external darlington collector voltage is sensed voltage.
by the voltage divider R2, R3. The voltage limitation
increases rising R2 or decreasing R3. NEGATIVE SPIKE PROTECTION
Due to the active circuit used, an Ro Co series net- If correct operation is requested also during short
negative spikes, the diode DS and capacitor Cs must
be used.

Figure 4 : Application Circuit.

8/11
 L497

mm inch
DIM. OUTLINE AND
MIN. TYP. MAX. MIN. TYP. MAX. MECHANICAL DATA

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
DIP16
Z 1.27 0.050

9/11
L497

mm inch
DIM. OUTLINE AND
MIN. TYP. MAX. MIN. TYP. MAX. MECHANICAL DATA
A 1.75 0.069

a1 0.1 0.25 0.004 0.009

a2 1.6 0.063
Weight: 0.20gr
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
SO16 Narrow
S 8˚(max.)

(1) D and F do not include mold flash or protrusions. Mold flash or potrusions shall not exceed 0.15mm (.006inch).

0016020

10/11
 L497

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quences 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 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 written
approval of STMicroelectronics.
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