STCS1_08 datasheet(10/17 Pages) STMICROELECTRONICS

10 / 17 page

Application information

STCS1

10/17

Application information

8.1

Reverse polarity protection

STCS1 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 STCS1 is able to control a LED current up to 1.5 A 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 Table 4: Thermal data section are the typical ones, in

particular RthJA depends on the copper area and the number of layers of the printed circuit

board under the pad. DFN8 and PowerSO-8 have an exposed die attach pad which

enhances the thermal conductivity enabling high power application.

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: 500 mA;

Figure 11.

Reverse polarity condition

PWM

GND

VCC

DRAIN

DISC

VIN

or similar

BAT46

PWM

GND

VCC

DRAIN

DISC

VIN

or similar

BAT46

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