L9686 datasheet(3/7 Pages) STMICROELECTRONICS

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FUNCTIONAL DESCRIPTION

The circuit is designed to drive the direction indi-

cator flasher relay. The application circuit shows

the typical system configuration with the external

components. Its consists of a network (R1 C1)to

determine the oscillator frequency, shunt resistor

(RS) to detect defective bulbs and two current lim-

iting resistors (R2/R3) to protect the IC against

load dump transients.

The lightbulbs L2,L3,L4,L5, are the turn signal in-

dicators with the dashboard-light L6. The S1

switch

position is sensed

across

resistor R2

and Rlamp by input 8. The flashing cycle is started

by closing S1 : then, after a delay time td typically

equal to 1.5 ms, the relay is actuated and the pin

3 goes high switching on the corresponding

lamps L2,L3, (or L4,L5). These lamps will flash at

the oscillator frequency not depending on the bat-

tery voltage value (8 - 18 V). The flashing cycle

stops and the circuit is reset to the initial position

when the switch S1 is open.

The lamp failure detection function senses the

current through the shunt resistor RS. When one

of the lightbulbs is defective the voltage drop

across RS is reduced to a half and the failure is

indicated by doubling the flashing frequency.

ELECTRICAL CHARACTERISTICS (– 20

°C< Tamb <, 100°C, 8V < VS < 18V unless otherwise speci-

fied.)

Symbol

Parameter

Test Condition

Min.

Typ.

Max.

Unit

Operating Voltage

V2 – V1

Clamping Voltage

see note 1

V2 – V3

Output Saturation Voltage

IRL = 250mA

1.7

Starter Resistance

see note 2

3.6

Ω

Oscillator Constant KN (normal

Operation)

Fn = 1/KnRoCo

Osc. Frequency

1.27

1.74

Temperature Coefficient of Kn

See Note 3

–1.5

⋅

10-3

°C

D.C.

Duty Cycle (normal operation)

Oscillator Constant KC

(lamp failure detection)

FC = 1KcRoCo

Osc. Frequency

0.53

0.74

DCLF

Duty Cicle (lamp failure

detection)

Current Consumption Relay off

Ipin 1

VS =8V

VS = 13.5V

S = 18V

2.2

2.7

3.3

3.9

4.3

4.7

Vth

Lamp Failure Threshold

(see note 4)

R3 = 220

Ω

VS = 13.5V

–20 < Tamb < 100

°C

Notes : 1.

This voltage is the threshold used to protect the circuit against overvoltage : if Vbat is > than this threshold, the relay will be on

and the voltage across the circuit wil l maintain constant increasing the current in the protective resistor R3.

This is the maximum value for operation. This value must be higher than 1 K Ohms in order to limit the current in pin 8 during

dumps. A recommended value for application should be 1,5 K Ohms.

The external leakage from the blinker unit to ground must be with an equivalent resistor higher than 5,6 K Ohms to avoid para-

sitic operation when the switch S1 is off.

This temperature coefficient is usefull to compensate the drift of the external timing network (R1,C1).

This threshold is calculated for a 20 m Ohm shunt. The threshold is dependant of Vbat as the bulb current.

L9686

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