STCS05A Datasheet, PDF (12/18 Pages) STMicroelectronics – 0.5 A max constant current LED driver

Application information
8
Application information
STCS05A
8.1
Reverse polarity protection
STCS05A 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.
Figure 15. Reverse polarity condition
V_IN
BAT46
or similar
+
V_CC
PWM
DRAIN
EN
DISC
SLOPE GND FB
8.2
12/18
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:
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: 350 mA;
– Package: SO-8;
– T_A = 50 °C;