UM0422

Detailed description

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Figure 3.

STCS1A application diagram for 0.5 A LED current

2

Detailed description

The STCS1 is designed to supply high power LEDs under the severe conditions of

automotive and industrial applications resulting in constant brightness and extended LED

lifetime.

The STCS1 is a BiCMOS constant current controller designed to provide a precise constant

current starting from a variable input voltage source. STCS1 is well suited for applications

requiring high voltage input and it is able to withstand automotive load-dump events up to

40 V. An external shunt resistor in the ground path of the connected LEDs is used to sense

the LED current. A regulation loop holds the voltage drop at the shunt resistor on a constant

level of 100 mV ( typ.). The potential difference across the sense resistor is compared to a

fixed reference voltage and the error is both amplified and used to drive the internal power

series pass device. Selecting the sense resistance permits adjusting the output current level

up to 1.5 A with a precision of

±10%. The integrated PWM input of the STCS1 allows LED

brightness regulation by pulse width modulation. The luminosity spread arising from the

LED production process can be compensated via software by an appropriate duty cycle

applied to the PWM pin. The STCS1A version has a specific pin which allows the user to set

of the slope of the edges of the LED current during the PWM dimming mode.

The device assembled on the demonstration board is the STCS1A, so the user will be able

capacitors. An open drain pin output provides information on load disconnection.

A more detailed description of STCS1 device can be found in the STCS1 datasheet.

V

IN

4.5V to 40V

STCS1A

C

BYP

0.1µF

C

SLOPE

10nF

C

DRAIN

0.47µF

R

FB

0.2O

Load disconnection

(Open Drain output)

OFF

OFF

ON

ON

PWM

EN

GND

SLOPE

VCC

DISC

FB

DRAIN

R

BAT46ZFILM

V

IN

4.5V to 40V

STCS1A

C

BYP

0.1µF

C

SLOPE

10nF

C

DRAIN

0.47µF

R

FB

0.2O

Load disconnection

(Open Drain output)

OFF

OFF

ON

ON

PWM

EN

GND

SLOPE

VCC

DISC

FB

DRAIN

R

BAT46ZFILM