STLC1

7/16

only when the OUT voltage is about 95% of its

final value. Such a start-up phase takes place

when only one input is enabled.

LOW SIDE DRIVER:

The purpose of the low side drivers is to connect

the LED cluster to ground, creating a path for the

current. Using external resistors, current flowing

into the LED cluster is set according to the

following formula:

where (see typical application schematic):

LSD over-current protection and under-current

diagnostic (see LAMP OUTAGE DETECTION

section) is performed by sensing the voltage on

resistors, when the corresponding LSD are

enabled.

If the voltage on

over-current protection acts by reducing the LSD

average current by switching ON and OFF the

LSD itself.

LAMP OUTAGE DETECTION

Resistors are used to sense the LED array

current. In case one or more LEDs fail (open

circuit) the current on the corresponding resistor

will drop due to the increased LED array

resistance. As soon as the voltage drop on

is

detected and the LMP-OUT pin becomes active

(low).

The

LAMP-OUTAGE

functionality

is

AND-ed with each input, that is a fault condition

can be detected only when the LED arrays are

enabled.

DIMMING

The dimming of the LED lamps can be obtained by

using the internal PULSE WIDTH controller (it

drives the LSD TAIL and STOP gates). The duty

cycle of this internal oscillator (whose frequency is

380Hz typical) can be set, forcing the voltage of

simple resistor divider (as shown in the typical

application scheme).

In this case the duty cycle percentage can be

calculated

with

the

following

approximated

formula:

The TS-PWM pin voltage, according to the

TABLE1 determines which LSD is PULSE WIDTH

CONTROLLER driven. Internal dimming can only

be performed on the TAIL and STOP arrays. The

TURN array can be externally dimmed (as well as

TAIL and STOP) by driving the corresponding

input witha a square pulse signal whose maximum

frequency must be 200Hz.

I

ARRAY

V

OUT

V

ARRAY

–

R

T

R

L

R

on

()

++

----------------------------------------------

=

DC%

3.8 if

R

C1

R

C1

R

C2

+

----------------------------

0.2

V

REF

--------------

≤

R

C1

R

C1

R

C2

+

----------------------------

100 Elsewhere

•

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