Datasheet

Application information STCS1
10/17
8 Application information
8.1 Reverse polarity protection
STCS1 must be protected from reverse connection of the supply voltage. Since the current
sunk from V
CC
pin is in the range of 450 µA a small diode connected to V
CC
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 V
IN
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 R
thJA
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:
P
D
= (V
DRAIN
- V
FB
) x I
LED
+ (V
CC
x I
CC
)
basing on this and on the thermal resistance and ambient temperature, the junction
temperature can be calculated as:
T
J
= R
thJA
x P
D
+ T
A
A typical application could be:
– Input Voltage: 12 V;
– 3 white LEDs with an typical V
F
= 3.6 V;
– LEDs current: 500 mA;
Figure 11. Reverse polarity condition
PWM
EN
GND
V
CC
DRAIN
DISC
FB
V
IN
+
or similar
BAT46
PWM
EN
GND
V
CC
DRAIN
DISC
FB
V
IN
+
or similar
BAT46