STCS05A datasheet(12/18 Pages) STMICROELECTRONICS

12 / 18 page

Application information

STCS05A

12/18

Application information

8.1

Reverse polarity protection

STCS05A must be protected from reverse connection of the supply voltage. Since the

current sunk from VCC pin is in the range of 450 µA a small diode connected to VCC is able

to protect the chip. Care must be taken for the whole application circuit, especially for the

LEDs, in fact, in case a negative voltage is applied between VIN and GND, a negative

voltage will be applied to the LED string that must have a total breakdown voltage higher

than the negative applied voltage in order to avoid any damage.

8.2

Thermal considerations

The STCS05A is able to control a LED current up to 500 mA and able to sustain a voltage

on the drain pin up to 40 V. Those operating conditions are however limited by thermal

constraints, the thermal resistances shown in the thermal data section is the typical ones.

The power dissipation in the device can be calculated as follow:

PD = (VDRAIN - VFB) x ILED + (VCC x ICC)

basing on this and on the thermal resistance and ambient temperature, the junction

temperature can be calculated as:

TJ = RthJA x PD + TA

A typical application could be:

– Input voltage: 12 V;

– 3 white LEDs with an typical VF = 3.6 V;

– LEDs current: 350 mA;

–Package: SO-8;

–TA = 50 °C;

Figure 15.

Reverse polarity condition

PWM

GND

SLOPE

DRAIN

DISC

or similar

BAT46

PWM

GND

SLOPE

DRAIN

DISC

or similar

PWM

GND

SLOPE

DRAIN

DISC

or similar

BAT46

PWM

GND

SLOPE

DRAIN

DISC

or similar

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